The 32nd Texas Symposium on Relativistic Astrophysics

Dec 11, 2023, 8:05 AM → Dec 15, 2023, 6:00 PM Asia/Shanghai

Tsung-Dao Lee Institute

Tsung-Dao Lee Institute

Since 1963, the Texas Symposium on Relativistic Astrophysics has been one of the most important international conferences in astronomy and physics.  Traditionally, it moves around the globe and takes place in different cities every two years.  The year 2023 marks the 60th anniversary of the Texas symposium series (see Trimble 2011 for the history), and the 60th anniversary of the discovery of the Kerr solution and of the identification of quasars.

The 32nd Texas Symposium on Relativistic Astrophysics will take place in Shanghai, China, from December 11 to 15, 2023. It will be hosted by Tsung-Dao Lee Institute, Shanghai Jiao Tong University.

Shanghai, situated on the estuary of Yangtze River, serves as the most influential economic, financial, international trade, and cultural center in East China.  It is also a popular destination for travelers seeking to experience the country's dynamic development.  In addition to its modernization, the city's multicultural flair endows it with a unique charm. New skyscrapers and old Shikumen together draw the skyline of the city. Western customs and Chinese traditions intertwine, making any visit to Shanghai a memorable experience.

Tsung-Dao Lee Institute (TDLI), initiated by Tsung-Dao Lee, a prominent Chinese-American physicist and Nobel laureate in Physics, was established in 2016 with strong support from various Chinese government agencies. The goal of TDLI is to develop into a top-level physics-astronomy research institute in the world, and to boost research and develop talents in basic sciences in China. Professor Frank Wilczek was the founding director, and Professor Jie Zhang is the current director.

The symposium will cover all major topics on high-energy and particle astrophysics, cosmology and relativity. It will include morning plenary sessions and afternoon parallel sessions which will function as mini-symposia in each sub-field. The plenary sessions will consist of ~45 min review talks. The afternoon sessions will feature oral talks (about 15-30 min) and poster contributions. 

We look forward to welcoming hundreds of international astronomers and physicists to Shanghai in December 2023!

SPAM WARNING:  We do not request any travel agency to book a hotel for participants. For hotel reservations, please directly contact the two designated hotels mentioned above. Alternatively, you are free to choose a hotel of your own preference.

                                                           Tsung-Dao Lee Institute Building

 

                                                                      The Bund （外滩）

 

                                                                          Yu Garden (豫园）

 

                                                                Zhujiajiao Ancient Town (朱家角古镇）

 

                                                                     Pan-fried Bun (生煎包）

 

Conference_Notification_for_SJTUer.pdf.pdf

More information about Tsung-Dao Lee Institute

Destination slip

• Conference-venue.pdf
• Everbright-International-Hotel.pdf
• Holiday-Inn.pdf

Documents download

• Certificate of Attendance.docx
• Certificate of Attendance for Poster and Oral Talk.docx
• Texas Symposium会议通知.pdf
• 参会证明.docx
• 参会证明-报告、poster.docx

videos texas32.mp4

Monday, December 11

8:40 AM → 10:20 AM Plenary Talk: Monday 08:40

Convener: Prof. Dong Lai (TDLI)

8:40 AM TDLI Director Welcome

Speaker: Prof. Jie Zhang (Tsung-Dao Lee Institute, SJTU)

8:45 AM The First Texas Symposium on Relativistic Astrophysics: A Historic Perspective, Sixty Years Later (online)

I will tie the symposium historically to among other things,

1. Oppenheimer and Snyder on Gravitational Collapse

2. The struggle of physicists to understand the Oppenheimer/Snyder paper; the view from Russia (Landau); the 1958 Solvay Conference confrontation between Wheeler and Oppenheimer.

3. The recent movie Oppenheimer, which I gather has been viewed widely in China (and on which I was a consultant). Oppenheimer, Teller and Wheeler.

4. The discovery of Quasars - Schmidt and Greenstein

5. The immediate recognition that Quasars may be powered in some way by gravitational collapse; Wheeler’s talk on gravitational collapse at the fFirst Texas Symposium. Oppenheimer at the Symposium.

6. The astronomical community’s slowness (in my opinion) to understand the relevance and importance of the Kerr solution. And therein I’d like tie my talk to Roy’s)

7. Tommy Gold’s after dinner speech at the First Texas Symposium

Speaker: Prof. Kip Thorne

9:10 AM The Kerr Solution, Black Holes, Quasars and Beyond (online)

I will talk about Kerr, its properties, its relationship to black holes, quasars, etc. Also, the reason why there is no actual reason to believe black holes have some mysterious singularity in the centre.

Speaker: Prof. Roy Kerr

9:30 AM Advances and challenges in solving the two-body problem in General Relativity

Since the discovery of the first binary black-hole merger in 2015, analytical and numerical solutions to the relativistic two-body problem have been essential for the detection and interpretation of nearly 100 gravitational waves from compact-object binaries. Future experiments will detect black holes at cosmic dawn, probe the nature of gravity, and reveal the composition of neutron stars with exquisite precision.Theoretical advances (of up to two orders of magnitude in the precision with which we can predict the relativistic dynamics) are needed to turn gravitational waves into precision laboratories of astrophysics, cosmology and gravity.

In this talk I will discuss recent advances in modeling the two-body dynamics and gravitational radiation, review the science that accurate waveform models have enabled with gravitational-wave observations, and highlight the theoretical challenges that lie ahead to fully exploit the discovery potential of increasingly sensitive detectors on the ground, such as Cosmic Explorer and Einstein Telescope and in space, such as LISA and TianQin.

Speaker: Prof. Alessandra Buonanno (Max Planck Institute for Gravitational Physics)

Texas-Symposium-AB.pdf

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 12:30 PM Plenary Talk: Monday 10:50

Convener: Prof. Ue-Li Pen (ASIAA)

10:50 AM The Future of Black Hole Imaging

The Event Horizon Telescope images of M87 and Sgr A have
opened a new era of resolved imaging of black holes at the event
horizon scale. I will describe how EHT measurements are made,
how they can be interpreted with the aid of state-of-the-art models,
what they teach us about black holes, and what the prospects are for
future experiments.

Speaker: Charles Gammie (University of Illinois)

Charles-texas_shanghai_23.pdf

11:40 AM The Discovery of Fast Radio Bursts

In this talk I will discuss the discovery of the Fast Radio Bursts (FRBs), short, millisecond-duration bursts of radio emission bright enough to be seen at cosmological distances. The discovery of FRBs was serendipitous, but not unlike the discovery of pulsars some 40 years prior. It took many years for FRBs to be accepted as true celestial objects but today they are valuable cosmological probes, with a sub-class exhibiting repeat bursts and at least one known source linked to a galactic magnetar.

Speaker: Matthew Bailes (Swinburne University of Technology)

TheDiscoveryAndScientificPotentialOfFastRadioBursts.pdf

12:30 PM → 1:40 PM Lunch Provided

1:40 PM → 3:20 PM Astroparticle: 13:30, Monday

Convener: Prof. Donglian Xu (T D Lee Institute)

1:40 PM Neutrino astronomy, astrophysical neutrino flavor ratio and BSM physics

Speaker: Carlos Argüelles-Delgado (Harvard)

1_Carlos_texas-symphosium-shanghai-china-2023-std-res.pdf

2:05 PM Multimessenger View of High-Energy Cosmic Neutrino Sources

The discovery of high-energy cosmic neutrinos opened a new window of astroparticle physics. Revealing the sources is also relevant for solving the long-standing puzzle about the origin of cosmic rays. I will discuss theoretical implications of the latest results on high-energy neutrino observations, including associations of high-energy neutrinos with galaxies hosting supermassive black holes, active galactic nuclei and tidal disruption events, and demonstrate the power of multi-messenger approaches. I will highlight the importance of the current and future neutrino and gamma-ray telescopes to probe non-thermal phenomena in the vicinity of supermassive black holes.

Speaker: Kohta Murase (Penn State University)

2_KohtaMurase_TXShanghai2023.pdf

2:30 PM High-energy neutrino emission from GRMHD accretion flows onto supermassive black holes

Accretion flows around supermassive black holes can emit the high energy neutrino and may significantly contribute to the IceCube neutrinos. The global structure of the magnetized accretion flows potentially affect the neutrino SEDs, while it has not yet been studied. We, therefore, carry out the calculation of SEDs of high energy neutrinos by using three dimensional general relativistic magnetohydrodynamic (GRMHD) simulation data of a radiatively inefficient accretion flow onto a supermassive black hole, assuming the pp collisions processes. The time evolution of the cosmic-ray protons SEDs are calculated by assuming the turbulent acceleration and the effects of compressions. We have found that the global structure effect, i.e., the superposition of the various neutrino SEDs emitted at different positions, appears as neutrino SEDs flatter than 1-zone models. The flatter neutrino SEDs will be consistent with the diffuse neutrino SEDs observed by IceCube.

Speaker: Tomohisa Kawashima

3_kawashima.pdf

2:42 PM Presupernova and Supernova Neutrinos

Neutrinos play essential roles in cooling the interiors of massive stars and serve as potential signatures of their evolution towards the eventual core collapse and supernova explosion. The intense neutrino burst from the supernova itself may reveal details of the explosion mechanism and of the formation of a neutron star or black hole. In rare supernovae where high-energy neutrinos are produced, low-energy neutrinos emitted near the central engine may interact with high-energy neutrinos to leave imprints on the latter. I will review the emission and detection of presupernova and supernova neutrinos, and the use of these neutrinos as probes of fundamental physics. I will also discuss how low-energy neutrinos can affect the spectrum and flavor composition of high-energy neutrinos produced in rare supernovae and similar sources.

Speaker: Prof. Yongzhong Qian (University of Minnesota)

4_qian_texas23.pdf

3:07 PM The féeton (B-L gauge boson) dark matter and its prediction in low-energy neutrino astronomy

The often-considered dark matter (DM) candidates, e.g., WIMP and ALP, are in tension with observations, which motivates new proposals for DM. The recently proposed féeton dark matter, a B-L gauge boson with a small mass and a feeble coupling to the standard sector constitutes a well-motivated dark matter model consistent with cosmology, Seesaw mechanism, and leptogenesis. This model predicts nontrivial neutrino signals decayed from dark matter in the Milky Way and distant galaxies, which are promising for the future with low-energy neutrino experiments. We name it the féeton dark matter.

Speaker: Weikang Lin (South-Western Institute for Astronomy Research)

Texas_Symposium2023_32nd_WeikangLin-2.pdf

1:40 PM → 3:20 PM Dark Matter: 15:50, Monday

Convener: Prof. Luca Visinelli (Shanghai Jiao Tong University)

1:40 PM eV axion dark matter

I will discuss some theoretical and experimental topics on eV axion dark matter. The cold axion dark matter can be produced thermally in the early Universe, or alternatively, it can be the inflaton itself. In both cases, the predicted mass range is around eV. The scenario can be probed by observing the dwarf spheroidal galaxies with state-of-the-art infrared spectrographs.

Speaker: Wen Yin (Tohoku)

eVDM.pdf

2:00 PM Patchy dark screening from dark photon

I will discuss anisotropic (patchy) screening induced by the resonant conversion of cosmic microwave background (CMB) photons into light bosons in the dark sector as they cross non-linear large scale structure (LSS). Using kinetically mixed dark photon as an example, I will show how this conversion between CMB photon and light dark photon naturally occurs for a wide range of dark photon masses. This conversion leads to new CMB anisotropies that are correlated with LSS, which we refer to as patchy dark screening, in analogy with anisotropies from Thomson screening. Due to the unique frequency dependence of this conversion optical depth, it is possible to distinguish this signal from the blackbody CMB anisotropies. I will discuss various two- and three-point correlation functions of the dark-screened CMB, as well as correlation functions between CMB and LSS observables, to project the sensitivity of future measurements to the kinetic mixing parameter and mass of the dark photon. I will demonstrate that an analysis with existing CMB data can improve upon current constraints by two orders of magnitude, while data from upcoming experiments such as CMB-S4, CMB-HD and upcoming LSS surveys can further improve the reach by another two orders of magnitude.

Speaker: Prof. Junwu Huang (Perimeter Institute)

Patchy dark screening TexasShanghai.pdf

2:20 PM Radio Search of Dark Matter

Dark matter is the dominant matter in the Universe. In this talk, I will introduce two major scenarios of dark matter: Axion dark matter and WIMP (Weakly Interactive Massive Particle) and show how radio telescopes can search and put constraints on their parameters. The first one is Axion, which is a compelling dark matter candidate of increasing scientific interests in recent years, and was originally postulated to solve the strong CP problem in particle physics. Axions can be converted into monochromatic radiation in the neutron star’s magnetosphere, constituting a unique window to probe its existence with a radio telescope. We used MeerKAT telescope for 10 hours to observe the isolated neutron star RX J0806.4-4123 in the UHF band. I will present the results of the constraints on Axion DM decay rate from the newly observed MeerKAT data. I will show that the (new) upper limit of the axion decay constant is in the mass range of 2.5-5 mu-eV (micro-Electronvolt), which corresponds to MeerKAT 544-1,088 MHz. The constraints from MeerKAT complements the laboratory-based axion dark matter searches and fills the gap between 810-1,090 MHz gap between ADMX and RBF experiments. In addition, we used China FAST telescope to observe the synchrotron emission of WIMP dark matter decay in COMA Berenices dwarf galaxy and obtained strong constraints on WMIP decay channels. I will analyze these two current results and give future prospects on using radio telescope to constrain dark matter.

Speaker: Prof. Yin-Zhe Ma (Stellenbosch University)

RadioDM_Texas_Dec2023_compressed.pdf

2:35 PM Pulsar timing residuals induced by wideband ultralight dark matter

The coherent oscillation of ultralight Fuzzy dark matter induces changes in gravitational potential with the frequency in the nanohertz range. This effect is known to produce a monochromatic signal in the pulsar timing residuals. Here we discuss a multifield scenario that produces a wide spectrum of frequencies, such that the ultralight particle oscillation can mimic the pulsar timing signal of stochastic common spectrum process. We discuss how ultralight dark matter with various spins produces such a wide band spectrum on pulsar timing residuals and perform the Bayesian analysis to constrain the parameters.

Speaker: Yun-Long Zhang (NAOC)

ZhangYL231211ShangHai.pdf

2:50 PM Primordial Black Holes, Dark Matter, and Gravitational Waves from QCD axion and axion-like particles

This talk is based on the papers arXiv: 2309.01739 and 2307.08185. I present a new mechanism of primordial black hole (PBH) formation from QCD axion in the context of the Peccei-Quinn symmetry breaking during inflation. The axion string-wall network re-enters horizon sufficiently late, so the closed domain walls that naturally arise in the network are sufficiently large to collapse into PBHs. Besides, free axions from the collapse of open walls bounded by strings account for dark matter. This framework yields a PBH abundance of 2.56% in dark matter. This fraction is independent of axion parameters and re-entering horizon temperature, as it is determined by the fixed proportion of closed walls in the network, governed by percolation theory. Intriguingly, our PBHs can naturally explain the gravitational microlensing events observed by the OGLE collaboration. In addition, the collapse of string-wall network will release gravitational waves (GWs), which is drastically different from that in the scaling regime. For certain parameter space of axion-like particles, such GW spectra can possibly explain the reported nHz stochastic GW background and can be tested by various GW interferometry experiments.

Speaker: Shuailiang Ge (Peking University)

ShuailiangGe_20231211-five.pdf

3:05 PM Pseudo-goldstones as light Dark Matter and First Order Phase Transitions

We explore the possibility that light Dark Matter (DM) existence is related to first order phase transitions (FOPTs) in the early Universe. In particular, DM particles may be pseudo-Goldstone bosons of spontaneously broken global symmetries beyond the Standard Model. In this case, a new scalar field can interact with the Higgs boson and it can be related to a first order electroweak phase transition. We show the case of Majoron DM from a L or B-L global U(1) spontaneous symmetry breaking, generating a Majorana mass for neutrino.
We will show FOPTs related to Majoron DM can generate a GW stochastic background signal that can be tested in future space-based interferometers such as LISA, TAIJI and Tianqing projects.
We discuss the complementarity of GW physics with colliders and neutrinoless double-beta-decays searches of Majorons.
We also mention the possibility of relating light DM to FOPTs below the electroweak energy scale as a possible explanation of NANOGrav 15yrs anomaly.

Speaker: Andrea Addazi (SiChuan University)

AATalk2023_TexasTDLi(2).pdf

1:40 PM → 3:20 PM GW Astrophysics: 13:30, Monday

Convener: Zhen Pan

1:40 PM Distortion of gravitational-wave signals by astrophysical environments

Measuring the mass and distance of a gravitational wave (GW) source is a fundamental problem in GW astronomy. The issue is becoming even more pressing since LIGO and Virgo have detected massive black holes that in the past were thought to be rare, if not entirely impossible. The waveform templates used in the detection are developed under the assumption that the sources are residing in a vacuum, but astrophysical models predict that the sources could form in gaseous environments, move with relatively large velocity, or reside in the vicinity of supermassive black holes. In this talk, I will show how the above environmental factors could distort the GW signals and result in a biased estimation of the physical parameters. In particular, I will highlight the ubiquity of such a bias among the LIGO/Virgo sources forming in active galactic nuclei. If not appropriately accounted for, the above bias may alter our understanding of the formation and evolution of the LIGO/Virgo black holes.

Speaker: Xian Chen

1-2023texas-symposium-17+3min.pdf

2:00 PM Effective-One-Body Numerical-Relativity waveform model for Eccentric spin-precessing binary black hole coalescence

Waveform models are important to gravitational wave data analysis. People recently pay much attention to the waveform model construction for eccentric binary black hole coalescence. Several Effective-One-Body Numerical-Relativity waveform models of eccentric binary black hole coalescence have been constructed. But none of them can treat orbit eccentricity and spin-precessing simultaneously. The current paper focuses on this problem. The authors previously have constructed waveform model for spin-aligned eccentric binary black hole coalescence $\texttt{SEOBNRE}$. Here we extend such waveform model to describe eccentric spin-precessing binary black hole coalescence. We calculate the 2PN orbital radiation-reaction forces and the instantaneous part of the decomposed waveform for a general spinning precessing binary black hole system in effective-one-body (EOB) coordinates.
We implement these results based on our previous $\texttt{SEOBNRE}$ waveform model. We have also compared our model waveforms to both SXS and RIT numerical relativity waveforms. We find good consistency between our model and numerical relativity. Based on our new waveform model, we analyze the impact of the non-perpendicular spin contributions on waveform accuracy. We find that the non-perpendicular spin contributions primarily affect the phase of the gravitational waveforms. For the current gravitational wave detectors, this contribution is not significant. The future detectors may be affected by such non-perpendicular spin contributions. More importantly our $\texttt{SEOBNRE}$ waveform model, as the first theoretical waveform model to describe eccentric spin-precessing binary black hole coalescence, can help people to analyze orbit eccentricity and spin precession simultaneously for gravitational wave detection data.

Speaker: Zhoujian Cao (Beijing Normal University)

2:20 PM gravitational waveforms and sciences with binary-extreme-mass-ratio inspirals

In this talk, I will introduce the binary-extreme-mass-ratio inspirals(b-EMRIs) which the whole compact binary captured by a supermassive black hole. B-EMRIs are multi-band gravitational wave sources both for space-borne and ground-base detectors. I will explain how we accurately calculate the waveforms, how to identify EMRI signals by the deep learning. Finally I will discuss the sciences related with the b-EMRIs.

Speaker: Wenbiao Han (SHAO)

2-bEMRIwaveforms.pptx

2:40 PM Electromagnetic counterparts of neutron star mergers

Besides canonical GRBs and kilonovae, neutron star mergers may be accompanied by different electromagnetic counterparts including: (1) precursors, (2) repeating outbursts from the merger product before its collapse into a black hole, and (3) unusual late GRB if the collapse is delayed by days. Physical mechanisms for the pre-merger and post-merger bursts will be discussed. Their detection would shed light on the magnetic fields pre-existing in the binary and generated by the merger.

Speaker: Andrei Beloborodov

3-Shanghai_mergers_2023.pdf

3:00 PM The Observational Signatures of Tertiary-Induced Mergers

While the LIGO/VIRGO/KAGRA (LVK) collaboration has observed $\sim 100$ binary black hole (BBH) mergers to date, the formation mechanisms of these BBHs remains poorly understood. The most promising approach to discriminating among the many proposed mechanisms relies on comparison of theoretical models to population-level statistics of the observed BBH events. However, the constraints derived from this process are often weak, as the complexity of most of these theoretical models introduces significant uncertainty into their predictions. As such, it is important to identify and characterize any well-constrained signatures of specific BBH formation channels. In this talk, we present the signatures of the classic tertiary-induced merger channel, where an initially wide BBH is induced to merge due to eccentricity excitation by a distant tertiary companion. This channel has a straightforward appeal due to the large observed occurence rate of high-mass stellar triples. We argue that a BBH formation via a comparable-mass triple produces a mass-ratio distribution inconsistent with the LVK data. Instead, we suggest that compact stellar binaries orbiting a larger-mass tertiary may be more consistent with the observed distributions to date.

Speaker: Yubo Su

4-suyubo-231211_Shanghai.pdf

3:10 PM BH binary formation in AGN disks: dynamics, hydrodynamics, and GW signatures

The possibility of binary black hole (BH) mergers in the accretion disks around active galactic nuclei (AGN) has recently received much attention. Studying the formation processes of these binaries allows us to more reasonably predict the rate and the observational properties of their mergers. In this talk, I will present our works on the mechanisms of forming tightly bound BH binaries in AGN disks via close encounters between two single BHs. First, using long-term N-body simulations, we find that two encountering BHs can form a bound binary via GW bremsstrahlung. This mechanism is important in low-density regions of the disks where the gas forces are weak. Mergers of the resulting binaries can have large eccentricities when entering the LIGO band and a broad distribution of orbital inclinations relative to the original AGN disk. Then, using a series of high-resolution 2D global hydrodynamical simulations, we demonstrate that binaries can also be formed by the collisions of the BHs' gaseous minidisks (which can produce a strong post-collision drag) if the host AGN disk is dense enough. Binaries assembled in this scenario may have compact semi-major axes and large eccentricities. We also diagnose the formation conditions of prograde and retrograde binaries using a 2D shearing-box model, and the results suggest that prograde binaries form at a slower rate than retrograde ones except when the gas density is sufficiently high.

Speaker: Jiaru Li (CIERA - Northwestern University)

5-Jiaru_talk-BBH-Shanghai-2023.pptx

1:40 PM → 3:20 PM Neutron Stars: 13:30, Monday

Convener: JinLin Han (National Astronomical Observatories of Chinese Academy of Sciences)

1:40 PM The short, high-DM FRB sky as revealed by Apertif + LOFAR

Identifying the physical nature of Fast Radio Burst (FRB) emitters requires good localisation of more detections, and broadband studies enabled by real-time telescope combinations. I will present the results from our Apertif FRB survey (ALERT), focusing on what we learned so-far about the connection between FRBs and neutron stars. ALERT performed wide-field, fully coherent, real-time FRB detection and localisation on the Westerbork interferometer. We detected a new FRB every week of observing, interferometrically localised to ~0.4-10 sq.arcmin, leading to confident host associations.

The 24 discovered FRBs are broad band and very narrow, of order 1ms duration. Only through our very high time and frequency resolution are these hard-to-find FRBs detected, producing an unbiased view of the intrinsic population properties. Combining these results with powerful population synthesis using FRBPOPPY allows us to determine the spectral index and the fluence distributions, constraining the emission mechanism. The fraction of Apertif bursts with multiple components is much larger than seen by CHIME/FRB: this morphological evolution with frequency is an important clue for, e.g., a magnetospheric origin. Temporal, 'micro-structure'-like behavior corroborates the hypothesis for the nature of the emission.

We further demonstrated that Apertif can localise one-off FRBs with an accuracy that maps magneto-ionic material along well-defined lines of sight. The solid detection rate next ensures a considerable number of new sources are detected for such study. The combination of detection rate and localisation accuracy exemplified by these ALERT FRBs thus marks a new phase in which a growing number of bursts can be used to probe our Universe.

We cojoined Apertif and LOFAR through real-time alerting. Using simultaneous radio data spanning over a factor 10 in wavelength, we detected FRB emission below 300 MHz for the first time. We thus show that the chromatic behavior of periodically repeating FRB 20180916B strongly disfavors scenarios in which absorption from strong stellar winds causes FRB periodicity. We establish that low-frequency FRB emission can escape the local medium and thus demonstrate that some FRBs live in clean environments -- a prerequisite for certain FRB applications to cosmology.

Speaker: Joeri van Leeuwen (ASTRON)

1vanLeeuwen_FRBs.Apertif.LOFAR_v02.pdf

2:05 PM Future Science with a Growing CHIME/FRB Sample

The radio transient phenomenon of fast radio bursts (FRBs), extragalactic flashes of radio emission occurring on ~millisecond timescales, continues to defy a definitive explanation. Ongoing monitoring campaigns from dedicated radio transient surveys have provided a rich catalog that have spurred a wide variety of analysis of the FRB population as a whole as well as specific sources displaying repeat bursts. The FRB survey operating on the Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB) has been a key contributor to this growing sample, detecting FRBs at a rate of ~few per day and poised to expand the current published FRB sample into the thousands. In this talk, I briefly review the recent science highlights from the first CHIME/FRB catalog and look to what a future sample of several thousand FRBs may tell us about these mysterious sources. In particular, I will focus on a special subsample of CHIME detected FRBs with corresponding voltage (baseband) data that enables significant improvements on localization and fluence measurement capabilities and additional science relating to microstructure and polarization.

Speaker: Ryan Mckinven (McGill University)

2talk_231209_texas_symposium_final_Mckinven.pdf

2:30 PM FRB physics: what, where and how?

I discuss the physical mechanism of fast radio bursts based on observational constraints and theoretical modeling. First, within the magnetar model of FRBs, I discuss mounting evidence of the magnetospheric origin of at least some bursts. I argue that FRBs can propagate within a dynamically distorted magnetosphere with relativistic particles. I present a mechanism involving inverse Compton scattering of low-frequency waves to generate coherent emission in FRBs. Finally, I discuss several other possible physical channels to produce some FRBs.

Speaker: Prof. Bing Zhang (University of Nevada, Las Vegas)

3Texas-Shanghai-Zhang.pdf

2:55 PM Investigating the Connection between Persistent Radio Sources and Fast Radio Bursts

The first repeating fast radio burst (FRB) was discovered in a dwarf host galaxy, and unveiled a surprising persistent radio source (PRS) co-located with the bursts and offset from its host center. At present, the prevailing progenitor model for this source invokes a young magnetar engine born from a superluminous supernova or long-duration gamma-ray burst based on their similar host environments. Testing this hypothesis motivates a systematic study of PRS emission in dwarf galaxies, to decipher the physical origins of PRSs and ultimately FRBs. Thus, we acquired new multi-frequency VLA and EVN observations of a sample of compact radio sources found in dwarf galaxies and offset from their galactic centers. I show that these sources exhibit various spectral shapes and variable light curves that are mostly dissimilar from the two PRSs confirmed to date, suggesting a diversity in the source population attributed to either physical origin or intrinsic properties. Finally, I present VLA and HST observations of the hyperactive FRB20201124A, where we place deep constraints on PRS emission, unveil signs of obscured star formation, and explore novel progenitor scenarios for this superlative event.

Speaker: Yuxin Dong (Northwestern University)

4TexasinShanghai23_YDong.pdf

3:07 PM The MeerKAT Pulsar Timing Array

The MeerKAT telescope owned and operated by SARAO in the Karoo in South Africa is a new radio telescope with outstanding properties for precision pulsar timing. The telescope comprises of 64x13.6m dishes with offset Gregorian feeds, enabling it to achieve a system equivalent flux density of less than 7 Jy over an octave of bandwidth from 856-1712 MHz. Unlike single dishes, interferometers can achieve remarkable polarisation purity that aids in precision timing. The small dishes have high slew rates and MeerKAT can typically achieve sub-microsecond timing on 85 millisecond pulsars (MSPs) in just a 12h session. Time transfer to UTC(NIST) enables systematic timing errors of order 5 nanoseconds. The large number of pulsars in the array, their accurate dispersion measures, high cadence (fortnightly) and 4+ year timing baseline makes the array very competitive in pulsar timing array science. The MeerTime Large Survey Project has measured 160,000 arrival times from 85 MSPs and probes a unique part of PTA phase space. The interesting noise analysis and search results will be presented.

Speaker: Matthew Bailes (Swinburne University of Technology)

3:20 PM → 3:50 PM Poster Session & Coffee Break

3:50 PM → 5:30 PM Accretion Processes: 15:50, Monday

Conveners: Hua Feng (Tsinghua University), Prof. Yosuke Mizuno (TDLI / Shanghai Jiao Tong University)

3:50 PM Highlights of Insight-HXMT on Accreting BH and NS X-ray Binaries

Insight-HXMT (hxmt.cn) is China’s first X-ray astronomy satellite and was successfully launched on June 15th, 2017. It carries three sets of collimated X-ray instruments with large effective areas, covering energy ranges of 1-15 keV, 5-30 keV, and 20-250 keV, respectively. This talk will review some highlights of the scientific results of Insight-HXMT, focusing on accreting black hole and neutron star X-ray binaries. Insight-HXMT has been performing well in orbit and is expected to operate for several more years. The observational program of Insight-HXMT is open world-wide.

Speaker: Shuang-Nan Zhang (Institute of High Energy Physics)

1_ZhangSN-HXMT-accretion-2023-12-11-Texas.pdf

4:15 PM Fast X-ray variability of a new high-mass X-ray binary MAXI J0709-159 / LY CMa observed by MAXI and NICER

MAXI J0709-159 is a new X-ray transient discovered by the MAXI all-sky survey on 2022 January 25 near the Galactic plane at $(l,b)=(229.3, -2.3^\circ)$. The follow-up observations with NICER and NuSTAR identified it with a new X-ray object located at a position consistent with a Be star, LY CMa, which has also been identified as B supergiant. From the transient X-ray behavior characterized by short (a few hours) activity duration, rapid (a few seconds) variability accompanied with spectral change, and large luminosity swing from $10^{32}$ erg s$^{-1}$ in quiescence to $10^{37}$ erg s$^{-1}$ at the outburst peak, the object was considered likely to be a Supergiant Fast X-ray Transient (SFXT), a subclass of supergiant X-ray binaries (Sugizaki et al. 2022). We analyzed the MAXI and NICER data in detail. The combined light curve reveals that the short outburst consists of several flare-up events, each lasting only a few minutes and rapidly changing in intensity. The variability power spectrum shows significant features suggesting quasi-periodic variations at 0.1-1 Hz. We discuss the origin of the quasi periodicity in terms of the mass accretion via interaction between the neutron-star magnetosphere and the stellar winds.

Speaker: Mutsumi Sugizaki (National Astronomical Observatories, Chinese Academy of Sciences)

2_sugizaki_texas2023shanghai_v2a.pdf

4:27 PM outburst of SLX 1746–331 observed by Insight-HXMT and NICER

The black hole candidate system SLX 1746–331 was back to business in 2023, after a long silence of roughly 13 years. An outburst was observed thoroughly by Insight-HXMT and NICER. The outburst is characterized by spectral dominance of the soft state, where the joint Insight-HXMT and NICER spectral analysis shows the temperature dependence of the disk flux follows T~3.98 in and thus suggests that the inner disk reaches to ISCO during almost the entire outburst. By assuming 0.3 LEdd for the peak flux and an inclination angle of zero degree, the lower limit of the compact object hosted in this system is estimated as 3.28±2.14M⊙. We also look into the relation of the disk temperature and disk flux for a sample of black hole systems, and by taking the disk temperature derived in the outburst of SLX 1746–331, such a relation results in a mass estimation of 5.2 ± 4.5M⊙.Finally, the spin of the compact object is constrained to larger than 0.8 with a spectral model of kerrbb.

Speaker: Shu Zhang et al. (INSTITUTE OF HIGH ENERGY PHYSICS,BEIJING)

3-ShuZhang-Texas-shanghai.pdf

4:39 PM Magnetic fields and outflows in X-ray binaries and changing look AGNs

Magnetic fields play important roles in black hole accretion disks. The outflows can be driven by the large-scale magnetic field co-rotating with an accretion disk, while the gas in the accretion disk may be arrested by the field if its strength is sufficiently high. In this talk, I will show how the hysteretic state transition in X-ray binaries (XRBs) can be modeled with the disk with magnetically driven outflows. Similar physical processes also take place in the disks of AGNs. We found that some important observational features of CLAGNs can be explained in the frame of the disk with magnetic outflows. We discovered that the radio emission of the XRB MAXI J1820+070 is delayed ~8 days compared with the X-ray flux, which is extremely long for an XRB. We interpreted it as evidence for the formation of a magentic arrested disk (MAD). In this scenario, the magnetic field is amplified by an expanding hot accretion flow in the soft-to-hard state transition, forming a MAD near the black hole around the time of the radio peak.

Speaker: Prof. Xinwu Cao (Zhejiang University)

4_XinwuCao-20231211_texas.pdf

4:59 PM Accretion regimes in accreting X-ray pulsars

Accreting pulsars are highly magnetized neutron stars in binary systems. They accrete material from the donor star and release the gravitational energy into X-rays. They generally exhibit complex timing and spectral variations at different accretion regimes depending on the accretion rate and the magnetic field. In the past few years, Insight-HXMT and NICER have provided broadband and high-cadence observations with complete coverage of several luminous outbursts of accreting X-ray pulsars. In this talk, we will introduce the detailed evolution of pulse profiles, spectral shapes and cyclotron resonant scattering features over a large luminosity range, and discuss the related theoretical models.

Speaker: Long Ji (SYSU)

5-LongJi_AXP.pdf

5:11 PM High Resolution Spectra of the Galactic Binary Pulsar 4U 1907+09

The accreting pulsar 4U1907-09 is one of ~35 high-mass X-ray binaries with known high
magnetic field strengths. A detected cyclotron resonance scattering feature (CRSF) at ~19 keV leads
to a field strength of ~$\sim 2\times10^{12}$ G. The system consists of a slowly-rotating (~440 s) X-ray
pulsar accreting from the stellar wind of an O8/9 supergiant. The X-ray pulsar is in a close
(~8.37 d) elliptical orbit (e $\sim$ 0.28) around its donor.
We conducted an analysis of four High Energy Transmission Grating observations with the
Chandra X-ray Observatory for a total of ~140 ks and one NuSTAR observation for 78 ks, at
different orbital phases, to probe the variation of the absorbing column around the orbit.
We measure line fluorescence at Fe K and possibly Si K and other lower Z elements to study
dense clumps in the wind of the pulsar's companion star. The details of the NuSTAR
observation are used to determine the higher energy continuum beyond 10 keV.

Speaker: Dr Jun Yang (Harvard Smithsonian Center for Astrophysics)

6-JunYang_Shanghai.pdf

3:50 PM → 5:30 PM Cosmic Explosions...: 15:50, Monday

Convener: Shuai Zha (Yunnan Observatories, Chinese Academy of Sciences)

3:50 PM Superluminous Supernovae

Shining tens to hundreds of times brighter than ordinary supernovae, superluminous supernovae provide an extreme view of power sources that may contribute to a range of cosmic explosions. Their high luminosities make them detectable throughout the high redshift universe where they may serve as tracers of their massive stellar progenitors and probes of the changes of gas in star-forming regions back to the epoch of the first stars. In this talk I will discuss the different types of superluminous supernovae, the roles that magnetars and circumstellar interactions play in shaping these rare events, and how we can use JWST to discover them at high redshifts. I will include discussion of some recent works offering new insights on the nature of the progenitors.

Speaker: Robert Quimby (SDSU)

21quimby_shanghai_2023.pptx

4:10 PM Supernova 2023ixf in M101

I will give an introduction of our studies on a recent type II supernova (SN 2023ixf) exploded in nearby galaxy M 101 at a distance of 6.85 Mpc. Such a close distance makes SN 2023ixf a nearby, bright stellar explosion that appears once in a decade, providing a rare apportunity to study the pre-explosion evolution of massive star and view the moment of shock breakout from the progenitor. Our instant multiwavelength observations, starting at ~1 hour after the explosion, reveal the shockwave pulse breaking out of a red supergiant (RSG) with a size of 450 solar radius and the shock propagation in an optically-thick dusty circumstellar shell. The earlytime light curves favor that the breakout and perhaps the distribution of the surrounding dust were not spherically symmetric. Analysis of the pre-discovery images (obtained 20 years before the SN explosion) indicate that SN 2023ixf originated from a RSG star with an initial mass of 11-14 M⊙. The derived mass loss rate is much lower than that inferred from the flash spectroscopy of the SN, suggesting that the progenitor experienced a sudden increase in mass loss when approaching the final explosion. Combining with early-time polarization observation, such a violent mass loss is likely a result of binary interaction.

Speakers: Xiaofeng Wang (Tsinghua University), Ms Gaici Li (Tsinghua University)

22SN2023ixf.pdf

4:30 PM Numerical modeling of neutrino quantum kinetics in high energy astrophysical phenomena

Neutrinos are key players in core-collapse supernova explosion (CCSN) and binary neutron star mergers (BNSM) as the dominant courier of energy and lepton-number. The neutrino kinetics including transport, neutrino-matter interactions, and neutrino flavor conversions (or neutrino oscillations) would account for triggering CCSN explosion, driving disk-outflows in remnants BNSM, and having influence on nucleosynthesis in these ejecta. Determining neutrino radiation field involving neutrino flavor conversion requires solving quantum kinetic equation, corresponding to an extension from classical Boltzmann equation. Although numerical modeling of neutrino quantum kinetics is a nascent field, a remarkable progress has been made in the last few years. In this symposium, I will review these progresses, paying a special attention to those relevant to CCSN and BNSM.

Speaker: Hiroki Nagakura (National Astronomical Observatory of Japan)

23Nagakura.pdf

4:50 PM The impact of rotation and turbulence on the standing accretion shock instability

The development of hydrodynamical instabilities during the first second after core bounce is a key ingredient in the explosion mechanism of massive stars. It affects the birth properties of neutron stars and black holes and generates specific signatures in gravitational waves and neutrinos.
The advective-acoustic mechanism of the standing accretion shock instability (SASI) is well established in a radial collapse but some properties of its spiral model in a rotating stellar core challenge our understanding since Walk+23. We use a perturbative study in the adiabatic approximation to reach an analytical understanding of the instability mechanism, improve the analytical estimate of SASI growth rate and oscillation frequency and explain the destabilizing effect of rotation.
By calculating the effects of viscosity and thermal diffusivity, we further clarify the relative roles of vorticity and entropy perturbations in the advective-acoustic mechanism. This calculation also allows us to reveal the sensitivity of SASI to pre-collapse turbulence, and demonstrate the importance of a fine radial resolution to correctly account for SASI in numerical simulations.

Speaker: Thierry Foglizzo (CEA Saclay)

24_20231211_Shanghai_Foglizzo.pdf

5:10 PM A 12.4 day periodicity in a close binary system after a supernova

Neutron stars and stellar-mass black holes are the remnants of massive star explosions. Most massive stars reside in close binary systems, and the interplay between the companion star and the newly formed compact object has been theoretically explored, but signatures for binarity or evidence for the formation of a compact object during a supernova explosion are still lacking. Here we report a stripped-envelope supernova, SN 2022jli, which shows 12.4-day periodic undulations during the declining light curve. Narrow Hα emission is detected in late-time spectra with concordant periodic velocity shifts, likely arising from hydrogen gas stripped from a companion and accreted onto the compact remnant. A new Fermi/LAT γ-ray source is temporally and positionally consistent with SN 2022jli. The observed properties of SN 2022jli, including periodic undulations in the optical light curve, coherent Hα emission shifting, and evidence for association with a γ-ray source, point to the explosion of a massive star in a binary system leaving behind a bound compact remnant. Mass accretion from the companion star onto the compact object powers the light curve of the supernova and generates the γ-ray emission.

Speaker: Ping Chen

25PingChen_SN2022jli_20231211.pptx

5:20 PM Uncovering Double-Detonation Type Ia Supernovae from Sub-Chandrasekhar-Mass White Dwarfs

While there is a broad consensus that Type Ia supernovae (SNe Ia) arise from explosions of carbon/oxygen (C/O) white dwarfs (WDs), the traditional scenario involving a Chandrasekhar-mass WD cannot account for the entire population. The detonation of a thin ($\sim$$0.01\,\mathrm{M_\odot}$) helium shell atop a $\sim$$1\,\mathrm{M_\odot}$ C/O core is a promising mechanism to explode sub-Chandrasekhar-mass WDs. These double-detonation explosions may be the origin of many normal SNe Ia. More massive helium shells and/or less massive C/O cores may explain some recently observed peculiar objects. In this talk, I will present observations of two SNe Ia discovered by Zwicky Transient Facility (ZTF), SNe 2020jgb and 2022joj. Their remarkable peculiarities point toward a double-detonation origin - (i) unusual color evolution and prominent continuous absorption in near-ultra-violet probe Fe-group elements formed in helium-shell detonations; (ii) tentative features of unburnt helium is detected in the near-infrared spectrum of SN 2020jgb; (iii) the nebular-phase spectra of SN 2022joj indicate a low Ni/Fe abundance ratio in the SN ejecta, which is only expected in the explosion of a sub-Chandrasekhar-mass WD. We performed the first systematic study on the host galaxies of peculiar double-detonation SNe Ia, finding a considerable diversity in their stellar populations. To close, I will briefly introduce the La Silla Schmidt Southern Survey (LS4), a new wide-field time-domain survey. With a customized color-evolution filter in the transient alert stream, LS4 will naturally power the discovery of both normal and peculiar double-detonation SNe Ia in a prompt and systematic way.

Speaker: Chang Liu (Northwestern University)

26TexasinShanghai23_CLiu.pptx

3:50 PM → 5:30 PM Cosmology with large-scale structure: 15:50, Monday

Convener: Zhongxu Zhai

3:50 PM Reconstructing the formation history of the observed universe

ELUCID is a method to reconstruct the initial linear density field from an input nonlinear density field,
employing the Hamiltonian Markov Chain Monte Carlo (HMC) algorithm combined with Particle-mesh (PM) dynamics.
My talk will describe its application and the constrained N-body and gas simulations in the SDSS volume. I will
show how to use the reconstruction to understand galaxies and gas in the cosmic web, as well as the underlying
physics.

Speaker: Houjun Mo (University of Massachusetts)

1_MO_Texas_Shanghai.pdf

4:10 PM When did first galaxies form?

The advent of the James Webb Space Telescope (JWST) has brought the study of early galaxy formation to a new level. Shortly after it began its scientific operation, JWST revealed a large number of candidate galaxies at redshift (z) greater than 11 when the universe was less than ~420 million years old, some of which could even be at z ~ 20 (age of the universe ~180 million years). This was completely unexpected by many, as the previously accepted picture (up to July 2022) would predict hardly any galaxies such early in time. Spectroscopy has confirmed some galaxies up to z = 13.2, which stimulates the building of a new consensus that galaxy formation happened much earlier in time than previously thought. Evidence from other lines of study, such as the metal abundance in galaxies at z ~ 8--9 and the confirmation of AGN at z ~ 10, all supports this new picture. This talk will give a brief overview of the up-to-date status of this frontier and will discuss the implications of this new picture to other important questions in cosmology.

Speaker: Haojing Yan (University of Missouri-Columbia)

2_YHJ_TexasShanghai.pdf

4:30 PM HI intensity mapping: results from MeerKAT and plans for the SKA

I will introduce the neutral hydrogen (HI) intensity mapping technique and its potential to constrain cosmology across a huge range of scales and redshifts. I will then discuss the latest results using the MeerKAT telescope and plans for the next few years. I will conclude with an highlight of the measurements expected with a future SKA HI intensity mapping survey and its synergies with other telescopes.

Speaker: Mario Santos (University of the Western Cape)

3_MarioSantos_Texas.pdf

4:50 PM Lyα Intensity Mapping with optical broad-band imaging

Lyα Intensity Mapping with optical broad-band imaging

Intensity Mapping is a promising observational technique, consisting in the tracing of emission lines on large angular scales, without resolving any particular objects. In this talk, I will present a new method to perform Lyα intensity mapping by studying the fluctuations in the background of broad-band images versus the Lyα forest of QSO spectra, in order to trace the unresolved Ly-alpha emission that permeates the inter-galactic medium (IGM). We perform a forecast for currently existing/ongoing surveys (DESI and the g-band data of its Legacy Imaging Surveys, DECaLS/BASS), and show that even the absence of any detection may place competitive upper limits in the total Lyα luminosity at z~3. We fully expect this signal to be detectable in the z~3 range with imaging data from already planned space missions (CSST) and ground surveys (LSST), and maybe even at z>3.5 (Euclid). Such detection would be the first imaging observation of the large-scale structure (>10 cMpc/h) of diffuse Ly-alpha emission, and would help constraining the total Ly-alpha luminosity (both from diffuse IGM emission and unresolved Lyα emitters), as well as shed light on the bias of this diffuse Ly-alpha emission as a tracer of large-scale structure. High SNR detections with future photometric surveys could even lead to the use of this Intensity Mapping technique as a cosmological probe to explore large-scale structure at a redshift range (z~3) that it is scarcely sampled by current galaxy surveys.

Speaker: Pablo Renard Guiral (Tsinghua University)

4_Pablo_lya_im_shanghai.pdf

5:00 PM Astrophysical challenges in the post-reionization intergalactic medium: relics from cosmic reionization

The high-redshift nature of the post-reionization IGM makes it a promising avenue to constrain the nature of dark matter since nonlinearities are not as prominent as in low-redshift alternatives. Nevertheless, to fully unlock 21 cm intensity mapping and the Lyman-$\alpha$ forest, which are the two primary cosmological probes of the post-reionization era; we must first account for their respective responses to the reionization process or otherwise face large biases in the inference of cosmological parameters from current/near-term instruments like DESI and SKA. In this talk, I will explain the origin of the imprints of reionization in both 21 cm intensity mapping and the Lyman-$\alpha$ forest, quantify the strength of this novel broadband systematic, and establish their dependence on epoch of reionization and cosmic dawn astrophysics. Furthermore, I will introduce mitigation/separation techniques that allow for unbiased Bayesian inference of cosmological parameters in the post-reionization era.

Speaker: Paulo Montero-Camacho (Peng Cheng Lab)

5_talk_pmc.pdf

5:10 PM Analysis of Matter Growth Perturbations and Cosmographic Parameters in Specific Modified Gravity

We examine the cosmic evolution of the growth of perturbations with respect to matter content at early and recent past era of the Universe under the framework of non-zero torsion cosmology. Some cosmographic parameters are also discussed. To analyze this cosmic scenario, we formulate the cosmic models with two dark matter considerations and apply spherical collapse formalism. We explore that for model-1 (pressure less matter), the density contrast starts growing in early era of the Universe and with the Universe's overall expansion, density contrast grows faster for different choices of torsion parameter. In model-2 (matter with non-zero pressure), the density contrast shows enormous growth as compared to overall expansion of the Universe for the perturbed region, which indicates the collapse of the perturbed region and formulation of new large scale matter or galaxy. Further, we analyze the behavior of the growth function for both models with different values of torsion parameter. For model-1, the growth function increases smoothly for different choices of torsion parameter but for the model-2 the behavior of the growth function with nonzero DM and torsion significantly deviates from pressureless DM with zero torsion. We also investigate different cosmographic parameters for both models and analyze their behavior with different choices of torsion parameter and Lambda CDM. The results show the power-law expansion rate of the accelerating Universe with respect to redshift function.

Speaker: Dr Abdul Jawad (Institute of Theoretical Physics and Cosmology)

6_Jawad Texas Talk 2023.pdf

5:20 PM Primordial fossils as a probe of parity violation

The primordial vorticity and gravity wave leave anisotropic imprints in the large-scale structure, known as the primordial fossils. The primordial vector and tensor fossils are directly sensitive to parity violations in the early Universe. I will present a new method to generate parity violating initial conditions for cosmological simulations and show that the tidal estimators can separate the parity-odd signal from the nonlinearities generated in the cosmic evolution. This provides a new way to constrain parity violating signals using the large-scale structure traced by galaxies.

Speaker: Hongming Zhu (NAOC)

Tuesday, December 12

8:40 AM → 10:20 AM Plenary Talk: 08:40, Tuesday

Convener: Prof. Jane Dai (The University of Hong Kong)

8:40 AM Supermassive Black Holes at the Centers of Galaxies

The orbit of the S2 star and event horizon scale imaging have provided the strongest evidence yet that supermassive black holes (SMBHs) exist at the Galactic Center and in M87. Neither technique, however, can be easily applied beyond these two galaxies. Instead, direct evidence for other SMBHs in the nearby Universe has relied on measurements and modeling of spatially resolved kinematics of integrated stellar light or rotating disks of gas close to the hole. I will review both the observational and theoretical challenges in this endeavor, and discuss some recent progress enabled by sensitive integral-field spectrographs on large telescopes and by new approaches in dynamical modeling of galaxies using the Schwarzschild orbit method.

Speaker: Chung-Pei Ma (UC Berkeley)

1-Chung-Pei Ma-TexasSym2023.pdf

9:30 AM Applied Black Hole Dynamics: Transients from Galactic Nuclei

Galactic nuclei are the densest stellar environments in the Universe, and their gravitational blenders produce frequent close encounters between combinations of stars and compact objects. These encounters, in turn, lead to a wide variety of transients. Some of these transients are electromagnetically luminous, such as tidal disruption events, quasi-periodic eruptions, and stellar collisions. Others are gravitational wave sources, such as extreme mass ratio inspirals or binary black hole mergers. I will review the different types of transients -- both electromagnetic and gravitational wave -- produced by stellar dynamics in galactic nuclei, with an emphasis on possible multimessenger signals.

Speaker: Nicholas Stone (The Hebrew University of Jerusalem)

Stone_Shanghai_Final.pdf

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 12:35 PM Plenary Talk: 10:50, Tuesday

Convener: Prof. Dong Lai (TDLI)

10:50 AM Neutron Star Mergers: New Frontiers in Computational Relativistic Astrophysics

Announcing the dawn of a new era of multi-messenger astrophysics, the gravitational wave event GW170817 – involving the collision of two neutron stars – was detected in 2017. In addition to the gravitational wave signal, it was accompanied by electromagnetic counterparts providing new windows into the different physics probed by the system. Since then, several gravitational wave events involving neutron stars have been discovered, with more expected over the next years.

In order to understand and interpret the physics of these events, it is necessary to model the intricate dynamics of such systems before, during and after merger, including the amplification of strong magnetic fields and the formation of hot and dense nuclear matter. Linking these multi-scale multi-physics dynamics to all observable channels (gravitational and electromagnetic) poses one of the main challenges of modern computational relativistic astrophysics and numerical relativity.

In this talk, I will discuss the state-of-the art numerical modeling of neutron star coalescence, including recent advances on the inclusion of advanced relativistic plasma and nuclear astrophysics in simulations.

Speaker: Elias Most (Caltech)

EliasMost.pdf

11:40 AM The First Evidence for Nanohertz-frequency Gravitational Waves

In June 2023, pulsar-timing array experiments across the world announced evidence for correlations in the timing properties of millisecond pulsars scattered across the Milky Way. The signature of these correlations is consistent with an all-sky, broadband, background of gravitational waves at nanohertz frequencies, washing through the Galaxy. I will present the analyses that led to these breakthrough findings, the potential origins of the signal, and discuss important questions that must be addressed in order for pulsar-timing arrays to become engines of further discovery.

Speaker: Stephen Taylor (Vanderbilt University)

4-STaylor_TheFirstEvidenceForNanohertz-FrequencyGravitationalWaves.pdf

12:15 PM CPTA progress and DR1.0

In the talk, we will present the results of high precision pulsar timing of 57 millisecond pulsars conducted using the the Chinese FAST 500-meter radio telescope. Particularly, we will highlight the gravitational wave searching efforts of the Chinese Pulsar Timing Array collaboration. More backgrounds and topics on pulsar timing, nanoHertz GW detection, and gravity test will be also covered. Future Chinese perspective in the related field will be also discussed.

Speaker: kejia lee (pku)

5-2023_CPTA_texas.pdf

12:35 PM → 1:40 PM Lunch (on your own)

1:40 PM → 3:20 PM Astroparticle: 14:00, Tuesday

Convener: Gwenael Giacinti (TDLI & SJTU)

1:40 PM VHE-UHE Gamma-rays from Relativistic Galactic Sources

Relativistic outflows are efficient particle accelerators, and TeV-PeV photons provide an extremely effective probe of these systems. I will discuss the latest observational results related to Galactic systems with relativistic outflows and associated gamma-ray emission, including pulsar wind nebulae and microquasars, and large-scale emission associated to particles that have escaped from such systems. Finally I will discuss the prospects for understanding the lifecycles and populations of these systems with the help of the new generation of ground-based gamma-ray instruments.

Speaker: Prof. Jim Hinton (Max-Planck-Institut für Kernphysik, Heidelberg)

1_TexasShanghaiHinton.pdf

2:05 PM LHAASO results on PeVatrons and Pulsar Wind Nebulae

LHAASO is a ground-based TeV-PeV gamma-ray instrument with an unprecedentedly high sensitivity at the ultrahigh-energy band (E>100 TeV). Measurements of UHE sources provide important clues to understanding long-sought origins of PeV cosmic rays or PeVatrons. I will introduce the recent progress of LHAASO's measurements on Galactic PeVatron candidates and pulsar wind nebulae, with paying particular he attention to a few most exciting sources.

Speaker: Ruoyu Liu (Nanjing University)

2_TEXAS-LHAASO_RYL.pptx

2:30 PM Particle Acceleration in Pulsar Wind Nebulae

Pulsar Wind Nebulae (PWNe) are the prototypical Galactic relativistic accelerators. They are the most promising astrophysical labs where high-energy astrophysical processes can be investigated in details. They are also among the best studied objects in the sky, at the forefront of observational and theoretical endeavors. I will briefly review the current status of our knowledge of these objects, with a focus on their role as particle accelerators, and non-thermal sources in the Galaxy, together with the latest observational results.

Speaker: Niccolo' Bucciantini (INAF - Osservatorio di Arcetri)

3_Bucciantini.pdf

2:55 PM Gamma-ray binaries at very-high-energies: particle acceleration and non-thermal emission

Surveys with ground-based Cerenkov telescopes (e.g., HESS, MAGIC, and VERITAS) and space-based gamma-ray detectors (e.g., Fermi, INTEGRAL, and AGILE) have discovered a new class of binary systems that emit luminous gamma-rays. Those binaries usually comprise a stellar-mass compact object in orbit with a massive star and emit broadband radiation with non-thermal spectra peaking beyond 1 MeV, distinguishing them from the well-known X-ray binaries. So far, less than ten such binaries have been found, and only two of them with compact objects have been identified as pulsars. Gamma-ray binaries are unique astrophysical laboratories for studying particle acceleration and physical properties of outflows from compact objects and massive stars. In the talk, I will briefly summarize the basic observational properties of detected gamma-ray binaries, and introduce our recent theoretical studies on the multi-wavelength emission mechanisms of these systems.

Speaker: Shangming Chen (TDLI)

4_Chen Shangming_TeV binaries.pdf

3:07 PM Multi-messenger Study of Galactic Diffuse Emission with LHAASO and IceCube Observations

With the breakthrough in PeV gamma-ray astronomy brought by the LHAASO experiment, the high-energy sky is getting richer than before. Lately, LHAASO Collaboration reported the observation of a gamma-ray diffuse emission with energy up to the PeV level from both the inner and outer Galactic plane. In these spectra, there is one bump that is hard to explain by the conventional cosmic-ray transport scenarios. Therefore, we introduce two extra components corresponding to unresolved sources with exponential-cutoff-power-law (ECPL) spectral shape, one with an index of 2.4, and 20 TeV cutoff energy, and another with index of 2.3 and 2 PeV cutoff energy. With our constructed model, we simulate the Galactic diffuse neutrino flux and find our results are in full agreement with the latest IceCube Galactic plane search. We estimate the Galactic neutrino contributes of $\sim 9\%$ of astrophysical neutrinos at 20 TeV. In the high-energy regime, as expected most of the neutrinos observed by IceCube should be from extragalactic environments.

Speaker: Chengyu Shao (Sun Yat-sen University)

5_multimess_scy.pdf

1:40 PM → 3:20 PM GW Astrophysics: 14:00, Tuesday

1:40 PM Neutron star mergers, kilonovae, and the synthesis of heavy elements

This talk reviews recent developments related to simulations of neutron-star mergers, the generation of kilonovae, and the synthesis of rapid neutron capture (r-process) elements in the Universe. In particular, the talk will discuss recent constraints on r-process nucleosynthesis from the O3 run of the LVK gravitational-wave detectors. It will also focus on recently identified magnetohydrodynamic jet-formation mechanisms in neutron-star mergers and their implications for the generation of GW170817-like massive blue and red kilonovae and short gamma-ray bursts.

Speaker: Daniel Siegel

2:00 PM GW170817B - THE FIRST DIRECT DETECTION OF GRAVITATIONAL WAVES ASSOCIATED WITH A GRB

On August 17, 2017, GW170817 showed the merger of a double neutron star system. Model-independent data analysis by butterfly-matched filtering, a novel time-symmetric data analysis method with sensitivity on par with CBC, reveals a continuation in GW170817B starting 0.92±0.08 s after final coalescence. It signals the birth of the central engine of GRB170817A significant at 5.5 σ (van Putten & Della Valle, 2023, A&A, 669, A36), emitting 3.5% M-Solar c2 in gravitational radiation. GRB170817A is hereby identified with black hole spin-down following the delayed gravitational collapse of the initial post-merger remnant - a hypermassive neutron star. GW170817B provides the first evidence of Kerr black holes as objects in Nature by GW-calorimetry (van Putten & Levinson, 2002, Science, 295 1874).

Speaker: maurice van putten (INAF-OAS, Sejong University)

2-vanPuttenGW.pdf

2:20 PM On the Formation of Double Neutron Stars in the Milky Way Galaxy

The detection of gravitational wave events has stimulated theoretical modeling of the formation and evolution of double compact objects (DCOs). However, even for the most studied isolated binary evolution channel, there exist large uncertainties in the input parameters and treatments of the binary evolution process. So far, double neutron stars (DNSs) are the only DCOs for which direct electromagnetic observations are available. In this work, we adopt a population synthesis method to investigate the formation and evolution of Galactic DNSs. We construct 216 models for the formation of Galactic DNSs, taking into account various possible combinations of critical input parameters and processes such as mass transfer (MT) efficiency, supernova type, common envelope (CE) efficiency, neutron star kick velocity, and pulsar selection effect. We employ Bayesian analysis to evaluate the adopted models by comparing with observations. We also compare the expected DNS merger rate in the Galaxy with that inferrd from the known Galactic population of Pulsar-NS systems. Based on these analyses we derive favorable range of the aforementioned key parameters.

Speaker: Prof. Xiangdong Li

3-On the Formation of Double Neutron Stars.pptx

2:40 PM Testing the importance of the AGN channel for stellar binary black hole mergers

The origin of stellar black hole binary (sBHB) mergers detected by the LIGO/Virgo interferometers is debated. One viable channel is the formation and merger of sBHB in the accretion discs surrounding active supermassive black holes. In this talk, i will review our observational strategy to investigate and assess a spatial correlation between Gravitational Wave detections and Active Galactic Nuclei. I'll then present our results, which pose the first direct and largely model independent constraints on the AGN channel. I will end with a discussion on the implications of our findings.

Speaker: Prof. Elena Maria Rossi (Leiden University)

2:50 PM Black hole mergers and accretion in AGN disks

Since the first discovery of a transient gravitational-wave signal by LIGO/Virgo, it has motivated many theoretical studies on how merging binary black holes (BBHs) form. Active galactic nucleus (AGN) disks have been proposed as promising locations for producing some of gravitational wave events. However, the validity of this AGN disk channel remains largely debatable due to the complexity of binary-disk interaction. In this talk, I will briefly introduce the recent updates of this AGN disk channel, and some of our works about binary black hole evolution in AGN disks.

Speaker: Dr Yaping Li (Shanghai Astronomical Observatory)

5. YLi-BBH.pptx

3:00 PM Probing stellar mass black hole orbits deep in galactic nuclei with quasi-periodic eruptions

Quasi-periodic eruptions (QPEs) are intense repeating soft X-ray bursts with recurrence times about a few hours from nearby galactic nuclei. The origin of QPEs is still unclear. Though many models have been proposed for explaining the QPE observations, most of them can only recover
a portion of diverse features of different QPEs. In this work, we revised the extreme mass ratio inspiral (EMRI) + accretion disk model, where the disk is formed from a previous tidal disruption event (TDE). In this EMRI+TDE disk model, the QPEs are the result of collisions between a TDE disk and a stellar mass black hole (sBH) orbiting around a supermassive black hole (SMBH) in galactic nuclei. This model is flexible and comprehensive in recovering different aspects of QPE observations, especially fitting the QPE light curves
and spectral evolution with high precision that alternative models hardly reach. In the framework EMRI+TDE disk, we find that all the observed QPEs are produced by EMRIs of low eccentricity and semi-major axis about $O(10^2)$ times gravitational radius of the central SMBH.
If this interpretation is correct, QPEs will be invaluable in probing the formation channels of EMRIs,
which is one the primary targets of spaceborne gravitational wave missions.

Speaker: Zhen Pan (TDLI)

6-Zhen Pan Texas.pdf

1:40 PM → 3:20 PM Gravitational Lensing: 14:00, Tuesday

Convener: Alessandro Sonnenfeld

1:40 PM Cosmology with Strongly Lensed Supernovae

An intriguing tension in the measurements of the Hubble constant H0, which sets the expansion rate of the Universe, has emerged in recent years. Independent determinations of H0 are important to assess the tension, which if verified, would imply new physics beyond the standard cosmological model. I will illustrate strong gravitational lenses with measured time delays between the multiple images as a way to measure H0. Exciting discoveries of the first strongly lensed supernovae offer new opportunities for measuring H0, and I will present recent advances. I will show the bright prospects of lensed supernovae as an independent and competitive cosmological probe.

Speaker: Sherry Suyu (Technical University of Munich / Max Planck Institute for Astrophysics)

23-1212Suyu_TexasSymposium_Shanghai_wide16-9.pdf

2:05 PM From cosmic lasagna to space-time spaghetti -- obtaining the least-model-dependent strong gravitational lensing probe

Strong gravitational lensing has advanced as a standard probe to map mass densities of cosmic structures or to try and infer parameters of the cosmological concordance model, like the Hubble Constant. Almost all approaches use a global assumption of the light-deflecting mass distribution at a specific redshift and fit the observed data to this model. With increasing data quality, the parameter space of these models becomes computationally costly to scan for optimum values. Besides this, degeneracies arise and there may be several best-fit models for a given set of observables.

In this talk, I will introduce those properties of a light-deflecting cosmic structure that can be uniquely and directly determined from observables without any global model assumption. They constitute the maximum information common to all model-based mass maps and require less than a second of computing time [1]. The derivation of these characteristics also reveals the most general class of degeneracies and a simple physical interpretation of all invariance transforms that can be applied to the equations of the single-plane formalism, leaving observable quantities unchanged [2].
As the formalism is only based on scale-free, purely gravitational light deflection, these local lens properties can be determined for any set of multiple images of a common background source independently and in exactly the same way on galaxy- or cluster-scales. Information can also be concatenated into a patch work of local lens properties to assemble a more global mass map and save resources at the same time.
As examples, I will showcase the power of this approach by two galaxy clusters: one that cannot be tackled by model-based approaches [3] and a second one where model-based approaches caused puzzling controversies [4].

References:
[1] https://arxiv.org/abs/1906.05285
[2] https://arxiv.org/abs/1809.03505, https://arxiv.org/abs/1904.07239, https://arxiv.org/abs/2203.06190
[3] https://arxiv.org/abs/2105.04562, https://arxiv.org/abs/2207.01630
[4] https://arxiv.org/abs/2306.11779

More information about the concept and further applications in cosmology:
https://thegravitygrinch.blogspot.com

Speaker: Jenny Wagner (Bahamas Advanced Study Institute & Conferences)

JennyWagner.pdf.pdf

2:30 PM The “Missing baryons” in the cosmic web—what is it? Where is it? How much?

Previous studies of galaxy formation have shown that only 10 per cent of the cosmic baryons are in stars and galaxies, while 90 per cent of them are missing. In this talk, I will present three observational studies that coherently find significant evidences of the missing baryons. The first is the cross-correlation between the kinetic Sunyaev-Zeldovich maps from Planck with the linear reconstructed velocity field. The second measurement is the cross-correlation between the thermal Sunyaev-Zeldovich effect with gravitational lensing map and we detect the cross-correlation for 13 sigma with RCSLenS and Planck data. The third study is to stack the pairs of luminous red galaxies and subtract the halo contribution, which leads to the detection of gas within the cosmic filaments. These detections coherently brings a picture of how baryons distribute in the cosmic web. I will briefly describe how these studies can be improved with future CMB-S4 and LSST observation data.

Speaker: Yin-Zhe Ma (Stellenbosch University)

baryon_Texas2023_compressed.pdf

2:45 PM Comparing Characteristic Gravitational Lensing Features in Black Hole Spacetimes of the Plebanski-Demianski Class

Einstein's field equations allow various different black hole solutions. Among these solutions the most famous are most likely the Schwarzschild and the Kerr spacetimes, which are both special cases of the so-called Plebanski-Demianski spacetime. Besides the Schwarzschild and Kerr spacetimes the Plebanski-Demianski spacetime also includes other solutions as special cases, among them the C-metric and the NUT metric. They describe a linearly accelerating black hole and a black hole with gravitomagnetic charge, respectively. The question is now how we can determine if an astrophysical black hole can be described by one of these spacetimes.
We will address this question using gravitational lensing for the three spacetimes with the most salient lensing features, namely the C-metric, the NUT metric, and the Kerr metric. For this purpose we will first outline how to solve the equations of motion analytically using elementary and Jacobi's elliptic functions as well as Legendre's elliptic integrals. Then we will fix an observer in the domain of outer communication and relate the constants of motion of the lightlike geodesics to latitude-longitude coordinates on the observer's celestial sphere. We will use the analytic solutions to write down the lens equations, calculate the redshift, and the travel time. Finally, we will discuss and compare the results and comment on how we can use them to place constraints on the spin parameter, the acceleration parameter, and the gravitomagnetic charge of a black hole.

Speaker: Torben Christian Frost (Kavli Institute for Astronomy and Astrophysics, Peking University)

TEXAS32_12122023_Frost.pdf

3:00 PM Detecting Strong Gravitational Lensing of Gravitational Waves with TianQin

We discuss the capability of TianQin to detect lensed MBHB signals. Three lens models are considered in this work: the point mass model, the SIS model, and the NFW model. The sensitive frequency band for space-borne \ac{GW} detectors is around milli-hertz, and the corresponding GW wavelength could be comparable to the lens gravitational length scale, which requires us to account for wave diffraction effects. In calculating lensed waveforms, we adopt the approximation of geometric optics at high frequencies to accelerate computation, while precisely evaluate the diffraction integral at low frequencies. Through a Fisher analysis, we analyse the accuracy to estimate the lens parameters. We also assess the impact on the accuracy of estimating the source parameters.

Speaker: Xinyi Lin

Lin_Xinyi.pptx

1:40 PM → 3:20 PM High-E Missions...: 14:00, Tuesday

Conveners: Dong Lai (TDLI), Shuangnan Zhang

1:40 PM Two flagship high energy astrophysics missions: HERD onboard the China space station and eXTP observatory

In this talk I will briefly introduce two flagship high energy astrophysics missions: HERD onboard the China space station and eXTP observatory. HERD is a large cosmic-ray experiment developed by a Sino-European consortium onboard China’s Space Station for operation around 2027, with unprecedented acceptance and energy range for direct measurements of cosmic-rays and electrons, as well as a very large field of view for gamma-ray sky monitoring in space. eXTP is a large X-ray observatory developed by a large Sino-European consortium for launch around 2029, carrying large arrays of X-ray timing, spectroscopy and polarimetry telescopes, as well as a wide field monitor.

Speaker: Shuang-Nan Zhang (Institute of High Energy Physics)

1-eXTP-2023-12-12-Texas.pdf

4_HERD 20231214-Texas.pdf

2:10 PM The Einstein Probe mission

The Einstein Probe (EP) is a space mission dedicated to X-ray time-domain astrophysics, and is to be launched in the near future. It carries two instruments. One is a wide-field X-ray telescope (WXT) with a 3600 square-degree FoV and moderate angular resolution of 5arcmin (fwhm) operating in the 0.5-4keV soft X-ray band. The other is a Wolter-I X-ray telescope (FXT) for deep follow-up observations in 0.3-10keV and precise source locating. The WXT is an imaging telescope making use of novel X-ray focusing technology of lobster-eye micro-pore optics, which improves the sensitivity and angular resolution over the previous and current X-ray monitors. Transient alerts will be issued quickly to trigger follow-up observations. The Einstein Probe is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES. This talk will introduce the mission and its current status. Initial results from the EP-WXT pathfinder mission LEIA will also be briefly presented.

Speaker: Weimin Yuan (National Astronomical Observatories, CAS)

2-Texas32-symp-yuan.pdf

2:35 PM Hot Universe Baryon Surveyor

Hot Universe Baryon Surveyor (HUBS) is a proposed X-ray mission that is dedicated to probing hot gas, which is theoretically postulated to permeate the circumgalactic space and the cosmic web, through means of high throughput, high resolution X-ray spectroscopy. On galaxy scales, the hot gas is thought to be a key component of galaxy ecosystems, produced by stellar or black-hole feedback processes that are presently not understood. In the cosmic web, the hot gas traces important physical processes of structure formation. Observationally, however, the hot gas turns out to be quite elusive, due to its (expected) very weak and diffuse emission in soft X-rays. HUBS aims at filling this void. In this presentation, we will describe the core scientific objectives of HUBS and the key technologies required.

Speaker: Prof. Wei Cui (Tsinghua University)

3:00 PM MASS: MeV emission line astrophysics with fine resolution CZT detectors

The MeV Astrophysical Spectroscopic Surveyor (MASS) is a conceptual Compton telescope using 3D position sensitive cadmium zinc telluride (CZT) detectors. The CZT detector works at room-temperature with a spectral resolution of 0.6% at 0.662 MeV, enabling us to construct a large format Compton telescope to measure astrophysical nuclear emission lines, and address astrophysical problems regarding nucleosynthesis, pulsars, relativistic jets, and even planetary formation. The technique will be demonstrated with a CubeSat flight in the near future.

Speaker: Hua Feng (Tsinghua University)

MASS_texas.pdf

3:20 PM → 3:50 PM Coffee Break

3:50 PM → 5:30 PM Accretion Processes: 16:10, Tuesday

Conveners: Prof. Yosuke Mizuno (TDLI / Shanghai Jiao Tong University), Yue Shen

3:50 PM Towards a new generation of reflection models for precision measurements of accreting black holes

Blurred reflection features are commonly observed in the X-ray spectra of accreting black holes. In the presence of high-quality data and with the correct astrophysical model, X-ray reflection spectroscopy can be a powerful tool to probe the strong gravity region of black holes, study the morphology of the accreting matter, measure black hole spins, and even test Einstein's theory of General Relativity in the strong field regime. In the past 10-15 years, there has been significant progress in the development of the analysis of these reflection features, thanks to both more sophisticated theoretical models and new observational data. However, the next generation of X-ray missions (e.g. eXTP, Athena, HEX-P) promises to provide unprecedented high-quality data, which will necessary require more accurate synthetic reflection spectra than those available today. In this talk, I will review the state-of-the-art in reflection modeling and I will present current efforts to develop a new generation of reflection models based on neural networks.

Speaker: Cosimo Bambi (Fudan University)

1_CosimoBambi_32TexasSymp.pdf

4:02 PM A Phase-Resolved View to the Low-frequency Quasi-periodic Oscillations from the Black Hole Binary MAXI J1820+070

Although low frequency quasi-periodic oscillations (LFQPOs) are commonly detected in the X-ray light curves of accreting black hole X-ray binaries (BHXRBs), their origin still remains elusive. We use Insight-HXMT observations to conduct phase-resolved spectroscopy in a broad energy band for LFQPOs from MAXI J1820+070. By employing the Hilbert-Huang Transform method, we extract the intrinsic QPO variability, and obtain the corresponding instantaneous amplitude, phase, and frequency functions for each data point. With well-defined phases, we construct QPO waveforms and phase-resolved spectra. By comparing the phase-folded waveform with that obtained from the Fourier method, we find that phase-folding on the phase of the QPO fundamental frequency leads to a slight reduction in the contribution of the harmonic component. This suggests that the phase difference between QPO harmonics exhibits time variability. Phase-resolved spectral analysis reveals strong concurrent modulations of the spectral index and flux across the bright hard state. The modulation of the spectral index could potentially be explained by both the corona and jet precession models, with the latter requiring efficient acceleration within the jet. Furthermore, significant modulations in the reflection fraction are detected exclusively during the later stages of the bright hard state. These findings provide support for the geometric origin of LFQPOs and offer valuable insights into the evolution of the accretion geometry during the outburst in MAXI J1820+070.

Speaker: Qingcang Shui (Institute of High Energy Physics)

2_QingcangShui-The32ndTexas_1820_10min.pdf

4:14 PM Accretion-modified stars in active galactic nuclei: theory and observations

There is increasing evidence for that stars including compact stars unavoidably exist in accretion disks of active galactic nuclei. These stars are rapidly accreting and thus have tracks different from field stars, leading to dramatic increases of metallicity and outbursts from radio and gamma rays. Compact binary stars are formed in the disks and radiate gravitational waves after they merge. AGNs are ideal laboratories of multi-messager astronomy.

Speaker: Prof. Jian-Min Wang (IHEP)

3_Jian-minWang_AMS_Shanghai.pdf

4:39 PM Interplay between the Nearby Massive Black Holes and Their Close Environment

The feeding and feedback of weakly accreting massive black holes (MBHs) remain challenging to study both observationally and theoretically. We present our recent effort in understanding the interplay between some of the nearest MBHs and their immediate environment, based on multi-wavelength observations and hydrodynamic simulations. Outstanding questions for future study are also highlighted.

Speaker: Zhiyuan Li (Nanjing University)

4_ZhiyuanLi_LLAGN_TexasShanghai2023.pdf

4:59 PM Observational properties and physical mechanism for Changing-look AGNs

Change-Look AGN (CLAGNs) shown with disappear/re-appear of broad lines or strong variation of X-ray absorption in a couple of years have challenged the AGN unification model. The physical mechanism for changing look is still unclear. I will review the observational properties of CLAGNs (e.g. evolution of spectral energy distribution, variability in multiwavebands, etc.). We propose that most of CLAGNs may be caused by the change of radiative efficiency at Eddington ratio ~1%, where the accretion modes have changed. The CLAGNs stay in a transitional stage of galaxies, which transit from AGNs to quiescent stage or vice versa.

Speaker: Prof. Qingwen Wu (huazhong university of science and technology)

5_QingwenWu_AGN_202312shanghaiTexas.pdf

5:11 PM Poster flash talk

6_poster_flash_talk.pdf

5:11 PM Thermal bremsstrahlung emission from accretion disc in non-Kerr spacetime

The study of accretion flow for astrophysical sources like active galactic nuclei (AGNs), black hole X-ray binaries (BHXRBs), etc., is essential to understand their spectral features. Nowadays, theorists hugely focused on the alternative gravity theory to explain some distinctive observational results from the usual Kerr BH. One such emerging non-Kerr spacetime is the Johannsen-Psaltis (JP) metric, which is described by a deformation parameter in addition to the mass and spin of BH. Also, based on spacetime parameters in JP metric, the central object can become a BH or naked singularity (NS). However, isolating BH and NS objects by the accretion disc theory is very challenging. The disparity between the disc properties around these objects has been reported in the literature. But, no one considers the transonic accretion flows, which are yet to be explored. Motivated by this, we explore the spectral properties of accretion disc around BH and NS objects by studying the transonic accretion flow in the JP non-Kerr background. To do this, we numerically solve the energy and momentum equations under the framework of general relativistic hydrodynamics. We find all classes of accretion solutions in the parameter space of the flow energy and angular momentum. Then, we calculate corresponding disc luminosity (L) and spectral energy distributions (SEDs) by considering thermal bremsstrahlung emission. It is observed that I-type solutions generate high L and SEDs compared to the remaining solutions for both BH and NS models. Moreover, for BH model, SEDs for O and A-type solutions significantly differ from W and I-type solutions, especially for low energy accretion flow. On the other hand, for NS model, SEDs for different accretion solutions are identical in the whole parameter space. Most importantly, from a comparative study between the SEDs at a given flow parameters, we find that a NS object can produce a higher luminous power spectrum than a BH. These results open a window to find the nature of central singularities through the spectral analysis of accretion disc.

Based on the works: 1. arXiv:2308.12839; 2. Phys. Dark Univ. 37 (2022) 101120

Speaker: Subhankar Patra (Indian Institute of Technology Guwahati)

SubhankarPatra_poster_Texas2023.pdf

5:12 PM Testing The Kerr Paradigm Through Synchrotron Radiation

General Relativity has been tested in weak field regimes but in strong gravity regimes still to be verified. The strong gravity regime with synchrotron radiation is not yet explored. Synchrotron emission traces magnetic field and cosmic ray electrons. EHT observations show strong synchrotron radiation near black hole horizon. This paper presents test of strong gravity regime using synchrotron radiation. By adopting Cardoso, Pani, Rico (CPR) [Phys. Rev. D 89, 064007 (2014)], we first investigate effect of model parameters including spin parameter, inclination angle, magnetic field and nonthermal spectral index of synchrotron radiation of Kerr space time on photon flux number density. Then, we extend it to CPR space time as this model deviates from Kerr space time. We also mock 10 data observations. Using a bayesian inference approach we fit model parameters including spin and deformation parameters of CPR metric . We considered both Kerr and CPR space time as reference case of model comparison. Assuming uniform/gaussian prior for all parameters, we can constrain all parameters. Assuming gaussian prior for spin parameter and uniform prior for deformation parameters of metric, the spin parameter can be constrained but the deformation parameters can not be constrained. Thus, synchrotron radiation provide a tool to explore strong gravity regime.

Speaker: Dr Masoumeh Ghasemi Nodehi (Xinjiang Astronomical Observatory)

Ghasemi-Nodehi_posterTexas.pdf

5:14 PM Shadow Cast by a Rotating Black Hole

In this paper, we study the shadow cast by a rotating black hole which turns out to be a dark region covered by a deformed circle. We then derive the relevant photon orbits and discuss the effects of black hole parameters on the silhouette of the shadow. We observe the change in the size as well as the shape such as deviation from the perfect circle, of the shadow with variation in the black hole parameters. In view of the optical properties of the black hole, the shadow region is supposed to be equal to the high energy absorption cross section. According to this perspective, we also explore the rate of energy emission. Moreover, we introduce plasma background and discuss its influence on the nature of the shadow, such as shape, size as well as the rate of energy emission.

Speaker: Dr Sehrish iftikhar (Lahore College for women University, Lahore, Pakistan.)

5:15 PM The Hard-to-soft transition of GX 339-4 as seen by Insight–HXMT

The nature of the state transition of black hole X-ray binaries has been debated for decades. We present an analysis of the relativistic reflection spectra of GX 339–4 during the hard-to-soft transition of its 2021 outburst observed by Insight–HXMT. The transition is accompanied by an increasing temperature of the disk and a softening of the corona emission, while the inner disk radius remains stable. If we include the Comptonization of the reflection spectrum, the scattering fraction parameter is found to decrease during the state transition. Our results support the scenario in which the state transition is associated with variations in the corona properties. The data also allow to measure parameters of the system, e.g. we find a high black hole spin (a* > 0.86) and an intermediate disk inclination angle (i ~ 35–43 deg) of the system.

Speaker: Honghui Liu (Fudan University)

5:16 PM Wideband study of black hole X-ray binaries observing by XTE: time delay between Compton and optical and Infrared flare

We investigate the all publicly available observations of black hole binaries in the RXTE archive. We also search the optical and infrared date during the corresponding epochs. It is widely observed that during the rising and decaying state, there is a high probability that the Compton luminosity manifests as a flare through the process of model fitting and subsequent calculations of luminosity. We analysis the time lags between OIR(optical and infrared) and Compton luminosity by using CCF. We find in the rising state the OIR flare are always antecedent to Compton luminosity range from 2 days to 13 days. On the contrary in the decaying state the OIR flare always lag to Compton luminosity range from 6 days to 36 days, but it also has exception, the decaying state of GX 339-4 during MJD 54050-54450, the OIR flare is antecedent to Compton luminosity.

Speaker: Dizhan Du (Zhejiang University)

5:17 PM Utilize EHT to search for axions.

Axion will be produced massively around a spinning black hole through superradiance mechanism. Such axion cloud will rotate the polarization angle of passing photons, creating an oscillating polarization direction for photons from supermassive black hole. EHT has provided great resolution on image of M87* black hole. We will utilize the information EHT gathered to put a stringent constraint on axions by pixel analysis, which could be a brand new pipeline for many possible searched for new physics beyond SM.

Speaker: Yuxin Liu (International Centre of Theoretical Physics, Asia-Pacifc)

5:18 PM A Study of the Continuum Emission Spectrum from the Central Engine in Narrow-line Seyfert Galaxies

Accretion disks around black holes are considered to be the physical source of high-energy emissions in objects such as quasars and active galactic nuclei. Some famous models, such as $\alpha$-model, slim model and ADAF model, are often employed to explain various observational phenomena under different conditions, and they have achieved significant success. However, these models do not describe how outflows are produced during super-Eddington accretion, and most recent studies have not considered the structural differences in the accretion disk along the vertical direction. A supercritical accretion disk model, proposed by (Cao & Gu 2022), suggests that when the accretion rate is high, the radiation intensity may exceed the gravitational confinement, driving matter to leave the accretion disk and form outflows. In this study, we investigate multi-wavelength continuum emission spectra data from the central engines of several narrow-line Seyfert galaxies, where the radiation exceeds the Eddington luminosity. We employ an empirical formula introduced by (Chiang 2002) for the frequency correction of the blackbody spectrum, considering the thermal emission from the corona. By fitting the observed data using this formula, we obtain good fitting results and constrain important physical parameters of these systems. Our findings indicate a certain level of credibility for the accretion disk model with radiation-driven outflows.

Speaker: 海潮 许 (浙江大学)

HaichaoXu_poster.pdf

poster.pptx

5:19 PM spin of 4u 1543－47

To introduce work on the spin of black hole candidate 4u 1543-47. The data used in work is of the outburst during 2021.

Speaker: 佳诗 陈 (武汉大学)

5:20 PM Spectra and light curves of the radiative reprocessing in a stable envelope

The radiation reprocessing model, in which an optically-thick layer absorbs the high-energy emission from a central source and re-emits in longer wavelengths, has been frequently invoked to explain some optically bright transients such as tidal disruption events (TDEs). Previous studies on this model did not take into account either changing the envelope mass and the input luminosity or the frequency-dependent opacity. We study the radiative reprocessing in a steady-state and spherical envelope composed of pure hydrogen gas with the different envelope mass and the input luminosity. Frequency-dependent bound-free, free-free and electron scattering opacities are considered.
We present the numerical results of the emitted optical luminosity and soft X-ray luminosity with the different envelope mass and input luminosity. The results show that with the increase of the envelope mass, the soft X-ray luminosity will be lower and the optical luminosity will be higher. The results also show that the higher the input luminosity, the higher the soft X-ray luminosity, while the optical luminosity is almost constant. We apply our model to the optically bright TDEs: ASASSN14-li, ASASSN15-oi, and the X-ray bright TDEs: SDSS J120136.02+300305.5 XMMSL1 J061927.1-65531.

Speaker: Chun Chen (中山大学)

ChunChen_pre_shanghai_20231210.pdf

5:21 PM Numerical Simulations of Relativistic Radiatively driven Jets

Relativistic jets are associated with variety of astrophysical objects like Active galactic nuclei (AGNs), Microquasars,Gamma ray burts (GRBs). The jets in AGN and Microquasars originate from the accretion disk. As they travel through the region very close to the central object they interact with the intense radiation field of the accretion disk. We perform the axisymmetric numerical simulations of radiatively driven jets and show that the radiation field can accelerate the jets to relativistic terminal speeds. The jets start with a subsonic inner boundary conditions with a very small velocity and get accelerated to relativistic speeds as they gain momentum from the radiation field. We also show that the in addition to the acceleration, the radiation field also acts as a collimating agent.

Speaker: RAJ KISHOR JOSHI (ARIES, Nainital, India)

5:22 PM Moving Corona and the Line Profile of the Relativistic Broad Iron Emission Line

Iron fluorescence emission lines from X-ray binaries and active galactic nuclei are important diagnostic tools for studying the physical processes near the event horizon of both the stellar-mass black holes in X-ray binaries and the supermassive black holes in active galactic nuclei. In our work, we investigate the line profile of the relativistic broad iron lines from the cool accretion disk of a black hole due to the asymmetric illumination of a moving corona, which moves away from the disk with a relativistic velocity. Both the off-axis location and the radial velocity of the moving corona are considered. Our results clearly show that the illumination and the line profile are dependent on the position and velocity of the corona, since the disk region below the corona receives more flux, which is the most important factor affecting the line profiles. As expected, if the corona is close to the receding part of the rotating disk, the red peak is enhanced, while the blue peak is weakened in the broad line profile, and the central energy of the emission line is low. Conversely, if the corona is close to the approaching part of the disk, the blue peak is strong and the central energy of the emission line is high, even higher than the intrinsic energy of the emission line. Due to the beaming effect of the moving corona, the corona with high velocity illuminates the outer region of the disk, which leads to the red peak disappearing and there being only one blue peak in the profile of the emission line.

Speaker: Mr Yuan Feng (中国科学技术大学)

Poster-FengYuan.pdf

5:23 PM The Role of Outflow Feedback on Accretion of Compact Objects in Accretion Disk of Active Galactic Nuclei

Compact objects (COs) can exist and evolve in an active galactic nuclei (AGN) disk, triggering a series of attractive CO-related multimessenger events around a supermassive black hole. To better understand the nature of an embedded CO and its surroundings and to investigate CO-related events more accurately, we study the specific accretion process of a CO in an AGN disk and explore the role of outflow feedback. We show that the asymptotically isotropic outflow generated from the CO hyper-Eddington accretion would truncate the circum-CO disk and push out its surrounding gas, resulting in recurrent formation and refilling of an outflow cavity to intermittently stop the accretion. Applying this universal cyclic process to black holes (BHs) and neutron stars (NSs),we find that, even if it is above the Eddington rate, the mass rate accreted onto a BH is dramatically reduced compared with the initial gas captured rate and thus consumes little mass of the AGN disk; outflow feedback on an NS is generally similar, but possesses complexities on the existence of a stellar magnetic field and hard surface. We demonstrate that although outflow feedback itself may be unobservable, it remarkably alters the CO evolution via reducing its mass growth rate, and the AGN disk can survive from the otherwise drastic CO accretion overlooking outflow.

Speaker: 恳 陈 (南京大学)

KenChen_Taxes.pdf

5:24 PM Impacts of non-thermal emission on the images of black hole shadow and extended jets in two-temperature GRMHD simulations

The recent 230 GHz observations of the Event Horizon Telescope (EHT) are able to image the innermost structure of M87 and show a ring-like structure that agrees with thermal synchrotron emission. However, at lower frequencies, M87 is characterized by a large-scale jet with clear signatures of non-thermal emission. In this study, we investigate the impact of non-thermal emission on the black hole shadow images and broadband spectrum from various two-temperature GRMHD models utilizing different black hole spins and different electron heating prescriptions coupling with different electron distribution functions (eDFs). Through the comparison with GRRT images and SEDs, we found that when considering variable kappa eDF, parameterized prescription of $R-\beta$ model with $R_{\rm{h}}$ = 1 is similar to the model with electron heating in the morphology of images, and the SEDs at the high-frequency. However, the nuance between them could be differentiated through the diffuse extended structure seen in GRRT images, especially at a lower frequency, and the behavior of SEDs at low frequency. Compared with the thermal eDF, the emission from the nearside jet region is enhanced, and the peaks of SEDs shift left when we consider non-thermal eDF.

Speaker: Mingyuan Zhang (TDLI / Shanghai Jiao Tong University)

5:25 PM Physical Analysis of Rastall PFRF Black Hole Through Accretion Process

The adiabatic accretion onto the charged black hole surrounded by
perfect fluid radiation field (PFRF) in Rastall gravity is addressed
in this manuscript. For this purpose, mass accretion rate $\dot{M}$,
critical horizon radius and some other flow parameters are being
determined in the presence of polytropic fluid. Overall the process
is being done analytically. The location of critical points,
polytropic gas compression ratios and temperature profiles are also
being investigated for different versions of polytropic equation of
state. We also give the comparison of the location of critical
points with case of Schwarzschild black hole in which critical
points lies out side the horizon. Through above scenario, it is
found that charge $Q$ and Rastall parameter $N_{r}$ have deep
effects on the accretion process. It is also mentioned here that
under some constraints on parameters, our results reduce to
Schwarzschild and charged black holes results.

Speaker: Ghulam Abbas (National Astronomical Observatory Chinese Academy of Sciences Beijing China)

5:26 PM A possible overall scenario for the outburst evolution of MAXI J1820+070 revealed by Insight-HXMT

We study the spectral and temporal properties of the black hole X-ray transient binary MAXI J1820+070 during the 2018 outburst with Insight-HXMT observations. The outburst of MAXI J1820+070 can be divided into three intervals. For the two intervals of the outburst, we find that low-energy (below 140 keV) photos lag high-energy (140-170 keV) ones, while in the decay of the outburst, high-energy photons lag low-energy photons, both with a time scale of the order of days. Based on these results, the canonical hysteresis effect of the 'q' shape in the hardness-intensity diagram can be reformed into a roughly linear shape by taking into account the lag corrections between different energy bands. Time analysis shows that the high-frequency break of hard X-rays, derived from the power density spectrum of the first interval of the outburst is in general larger and more variable than that of soft X-rays. The spectral fitting shows that the coverage fraction of the hard X-rays drops sharply at the beginning of the outburst to around 0.5, then increases slightly. The coverage fraction drops to roughly zero once the source steps into the soft state and increases gradually to unity when the source returns to the low hard state. We discuss the possible overall evolution scenario of corona hinted from these discoveries.

Speaker: jingqiang peng (IHEP)

5:27 PM Interacting Kilonovae: Long-lasting Electromagnetic Counterparts to Binary Mergers in the Accretion Disks of Active Galactic Nuclei

We investigate the dynamics and electromagnetic (EM) signatures of neutron star–neutron star (NS–NS) or neutron star–black hole (NS–BH) merger ejecta that occur in the accretion disk of an active galactic nucleus (AGN). Since most of the radiation energy has converted from the kinetic energy of merger ejecta, we call such an explosive phenomenon an interacting kilonova (IKN). It should be emphasized that IKNe are very promising, bright EM counterparts to NS–NS/BH–NS merger events in AGN disks.
The peak luminosity of an IKN can be brighter than
10$^{44}$ erg·s$^{−1}$, with similarity to superluminous supernovae (SLSNe) and tidal disruption events (TDEs). So the IKN could be one of the most energetic stellar optical transients in the universe. One can observe that the UV-optical-IR emission of an IKN can exceed the AGN background. This makes an IKN a very promising EM counterpart of GW events in the AGN disk for observation.

Speaker: jia ren (nanjing university)

5:28 PM Black Hole shadow from Loop Quantum Black Hole

In this study, we delve into the observational implications of rotating Loop Quantum Black Holes (LQBHs) within an astrophysical framework. We employ semi-analytical General Relativistic Radiative Transfer (GRRT) computations to study the emission from the accretion flow around LQBHs. Our findings indicate that the intensification of Loop Quantum Gravity (LQG) effects results in an enlargement of the rings from LQBHs, thereby causing a more circular polarization pattern in the shadow images. We make comparisons with the Event Horizon Telescope (EHT) observations of Sgr A∗ and M 87∗, which enable us to determine an upper limit for the polymetric function P in LQG. The upper limit for Sgr A∗ is 0.2, while for M 87∗ it is 0.1. Both black holes exhibit a preference for a relatively high spin (a ≳ 0.5 for Sgr A∗ and 0.5 ≲ a ≲ 0.7 for M 87∗). The constraints for Sgr A∗ are based on black hole spin and ring diameter, whereas for M 87∗, the constraints are further tightened by the polarimetric pattern.
In essence, our simulations provide observational constraints to the effect of LQG in SMBH, providing the most self-consistent comparison with observation.

Speaker: Mr Hongxuan Jiang (Tsung-Dao Lee Insitute)

3:50 PM → 5:35 PM Dark Matter: 16:10, Tuesday

Convener: Prof. Luca Visinelli (Shanghai Jiao Tong University)

3:50 PM Probing properties of dark matter via stellar kinematics around Sagittarius A*

Precise measurements of the stellar orbits around Sagittarius A have established the existence of a supermassive black hole (SMBH) at the Galactic center (GC). In addition, the existence of extended mass distribution from dark matter, or novel interactions between dark matter and ordinary matter would imprint on the motions of stars in the innermost region of the GC. Using the Keck and VLT observations of orbits and motions of S-stars around Sagittarius A, we obtain stringent constraints on the density profile of dark matter distribution, as well as the coupling between dark matter and ordinary matter particles.

Speaker: Qiang Yuan (Purple Mountain Observatory)

1-2023_S2orbit_YuanQ.pdf

4:10 PM Self-Interacting Dark Matter

I will discuss recent progress on N-body simulations of self-interacting dark matter and their implications within the context of the latest astrophysical observations, including ultra-diffuse galaxies, strong lensing perturbers, and supermassive black holes. We will show that self-interacting dark matter provides a compelling explanation to diverse dark matter distributions in galactic systems.

Speaker: Haibo Yu (University of California, Riverside)

2-2023TexasShanghai_HaiboYu.pdf

4:30 PM The present and future of primordial black holes as dark matter

The primordial black hole (PBH) is a unique candidate for dark matter (DM). It does not require a new particle for DM and the inflationary perturbation explains both the initial condition and the growth promoter of the cosmological perturbation. So far, astrophysical or cosmological observations have constrained the PBH abundance tightly and the window for PBH-DM remains only at the asteroid mass range. As such a small BH is hard to observe directly, the stochastic gravitational wave (GW) background induced by the large density perturbation is expected to be indirect evidence. To make it robust evidence, the relation among the inflation model, the PBH abundance, and the GW spectrum should be clarified accurately. I would like to discuss what we can do about this problem in the next decade.

Speaker: Yuichiro Tada (Nagoya University)

3-TADA_12122023_noanime.pdf

4:50 PM Relativistic Bondi Accretion and the BEC Dark Matter Spike

We consider the spike mass density profile in a dark halo by self-consistently solving the relativistic Bondi accretion of dark matter onto a non-spinning black hole. We assume that the dark matter in the halo forming a Bose-Einstein condensate (BEC) is described by a self-interacting scalar field. In the hydrodynamic limit, we find that the accretion rate has a lower bound. The spike density profile can be solved piecewise, and the power-law index of the profile is less cuspy compared to the density profiles of dark matter models with Coulomb-like self-interaction.

Speaker: Wei-Xiang Feng

Texas_Shanghai_20231212(WXFeng).pdf

5:05 PM Detecting Dark Matter with the Multi-Messenger Observations of Supermassive Black Holes

When a strong gravitational field is present around an SMBH, dark matter with gravitational interactions can congregate and create an environment that is far more dense than it would be in other regions. In recent years, the orbital dynamics of the S-star near the galactic center (GRAVITY/Keck), the imaging of SMBH (EHT), the nanohertz stochastic gravitational wave (PTA), and the precise observations of massive galaxies in the early universe (JWST) have all contributed to our understanding of the physical processes near SMBH, particularly the signals that may be left behind by dense dark matter. Consequently, we employ these observations to investigate possible indications that the traditional dark matter candidates—WIMP, ULDM, ALP and PBH—may have left behind in the SMBH observations. Our findings can not only shed light on the role that dark matter played in the formation and evolution of SMBH, but they can also offer fresh physical motivations of future multi-band and multi-messenger observations of SMBH.

Speaker: Dr Guan-Wen Yuan (Institute of High Energy of Physics, CAS)

5-GW.Yuan_Texas.pdf

5:20 PM The wave nature of Fuzzy Dark Matter

Fuzzy dark matter (FDM) is made up of a very light axion of mass ~1e-22eV governed by the Schrodinger-Poisson equation. The wave nature of FDM exhibits novel phenomena which can be used to observational probe and constrain the FDM model. In this talk, I will discuss how the wave interference of FDM leads to density fluctuations, the formation of vortices and filaments, and oscillation of the soliton core at the halo centre. Besides, I will also discuss how to constrain the FDM model from gravitational lensing and stellar dynamics.

Speaker: Xinyu Li (Tsinghua University)

texas_fdm.pdf

3:50 PM → 5:30 PM Neutron Stars: 16:10, Tuesday

Convener: Bing Zhang (University of Nevada, Las Vegas)

3:50 PM Mysteries of fast radio bursts

In this talk, I will review the current understanding of the origin of FRBs, highlighting persisting enigmas such as FRB locations, magneto-environment, and long-term periodicity. Additionally, I will propose searches for rare polarized propagation effects to understand FRB sources.

Speaker: Dongzi Li (Princeton University)

23Texas_symposium_DZL.pdf

4:10 PM "Geometry" of Pulsars, Magnetar and Fast Radio Burst

Pulsars and Fast Radio Bursts (FRB) are radio astronomy's most energetic and "fast" phenomena. They are both possibly from "neutron stars". In this talk, I will introduce some of my group and collaborators' pulsars and FRB research using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), from pulsar spin-kick geometry, emission geometry, relativistic spin precession in double neutron stars, to the emission geometry of FRB bursts in the magnetar SGR J1935+2154.

Speaker: Prof. Weiwei Zhu (National Astronomical Observatories, Chinese Academy of Sciences)

ZhuWeiwei.pdf

4:30 PM Statistical properties of repeating FRBs, in comparison with earthquakes and solar flares

At least some repeating FRBs are thought to occur in magnetars, and the similarity of magnetar activity to earthquakes and solar flares has been discussed in the literature. Here I present a brief review of studies on the occurrence times and energies of repeater FRBs and their correlations. I then report on our recent work based on the two-point correlation function. We found many notable similarities between FRBs and earthquakes, while they are different from solar flares. Based on the results of this analysis, the mechanism of the FRB phenomenon and its relation to magnetars and neutron stars in general will be discussed.

Speaker: Tomonori Totani (Dept. Astronomy, Univ. of Tokyo)

3.pdf

4:50 PM Coherent probes of the universe with FRBs and Gravitational Waves

FRBs and gravitational waves are the first coherent cosmic sources that exhibit interference effects. These open the window for direct FRB microlensing time delay measurement and gravitational wave diffractive lensing, enabling new direct measures of the cosmic geometry.

Speaker: Ue-Li Pen (ASIAA)

4 (2).pdf

5:15 PM Poster introduction: one minute each

3:50 PM → 5:30 PM Plasma Astrophysics: 16:10, Tuesday

Convener: Longqing Yi (SJTU)

3:50 PM Fast dissipation of magnetic energy near compact objects

The release of magnetic energy through magnetic reconnection and turbulence cascades is a major process invoked in active compact objects -- neutron stars and accreting black holes. Energy dissipation in the compact objects occurs in a dense radiation field, which impacts the dissipation mechanism and generates copious electron-positron pairs. Radiation spectrum emitted by magnetic dissipation depends on the dimensionless compactness parameter set by the ratio of the released power to the object size. Recent detailed simulations of this process demonstrate a reasonable agreement with the observed X-ray spectra of magnetar bursts and the hard state of accreting black holes.

Speaker: Prof. Andrei Beloborodov

Tue1_Shanghai_plasma_2023.pdf

4:15 PM Upstream plasma waves and downstream magnetic reconnection in a reforming quasi-parallel shock

Both satellite observations and kinetic simulations of quasi-parallel shocks have revealed the existence of large-amplitude low-frequency plasma waves in the upstream as well as the occurrence of magnetic reconnection in the downstream, however, their relations is still unclear. In this paper, with the help of two-dimensional (2-D) particle-in-cell (PIC) simulation model, we investigate the long-time evolution (near one hundred of ion gyroperiods) of a quasi-parallel shock. Part of upstream ions are reflected by the shock, and then low-frequency magnetosonic waves with the wavelength tens of the ion inertial lengths are excited in the upstream. Detailed analyses have indicated that the dominant wave mode is excited due to the resonant ion-ion beam instability. Although the plasma waves are directed toward the upstream in the upstream plasma frame, they are brought by the upstream plasma flow toward the shock front and their amplitude is enhanced during the approaching. The interaction of the upstream plasma waves with the shock leads to the cyclic reformation of the shock front, and the reformation period is slightly larger than 10 gyroperiods. When crossing the shock front, these large-amplitude plasma waves are compressed and evolve into current sheets in the transition region of the shock. At last, both ion-scale and electron-scale magnetic reconnection can occur in these current sheets, accompanying with the generation of magnetic islands. Our simulation provides the explanation for the generation process of magnetic reconnection, which has been recently observed by the satellite observations in the downstream of the Earth’s bow shock.

Speaker: 全明 陆 (中国科学技术大学地球和空间科学学院)

Tue2_Texas-Quanming Lu.pdf

4:40 PM Non-thermal processes in relativistic outflows

Relativistic outflows are synonymous with non-thermal processes; the acceleration of energetic particles and their associated radiation. I will review Fermi-like mechanisms responsible for particle acceleration and their associated radiative signatures, focussing on particle acceleration occurring in steep gradient flow profiles, i.e. shocks and shearing flows. Further insights from recent laboratory experiments will be presented.

Speaker: Brian Reville (MPIK)

Tue3_Texas23_Reville.pdf

5:05 PM High-intensity laser driven collisionless electrostatic shock and ion acceleration in a multicomponent plasma

Shock waves in space, such as in supernova remnants and the bow shock of the earth, are collisionless shocks generated in collisionless plasmas, which are one of the most promising candidates for the sources of cosmic rays. Thanks to the development of high-power lasers, a new method of studying high-energy astrophysics, such as the formation and evolution of collisionless shocks, in the laboratory, Laser Astrophysics, is emerging. Recently, high-intensity laser-driven collisionless electrostatic shock ion acceleration is drawing attention [1-4]. In this scheme, upstream ions of the shock are reflected and accelerated in by the shock potential. In this talk, collisionless electrostatic shock formation and ion acceleration in a near-critical density multi-component plasma are investigated both in the 2D particle-in-cell simulation and experiments.

References
[1] D. Harberberger, et al., Nature Phys. 8, 95 (2012).
[2] R. Kumar, Y. Sakawa, et al., Phys. Rev. Accel. Beams 22, 043401 (2019).
[3] R. Kumar, Y. Sakawa, et al., Phys. Rev. E 103, 043201 (2021).
[4] Y. Sakawa, Y. Ohira, et al., Phys. Rev. E 104, 055202 (2021).

Speaker: Youichi Sakawa (Institute of Laser Engineering, Osaka University)

Tue4_1_231212 Texas_Sympo_ESshock_presen.pdf

Wednesday, December 13

8:40 AM → 10:20 AM Plenary Talk: 08:40, Wednesday

Convener: Prof. Bing Zhang (University of Nevada, Las Vegas)

8:40 AM The Landscape of Relativistic Stellar Explosions

I will review developments in the study of relativistic stellar explosions, systems in which a newborn compact object drives a transient powerful outflow. For decades, the only firmly established example was long‐duration gamma‐ray bursts, thought to represent the special case of a narrow ultra‐relativistic jet lasting seconds. However, in recent years the landscape has broadened dramatically because discovery methods have expanded from solely γ‐ray satellites to include time‐domain surveys at other wavelengths. The observed diversity likely arises from variations in end‐stage stellar evolution, compact‐object accretion, and jet physics.

Speaker: Anna Ho (Cornell University)

9:30 AM Plasma astrophysics of high-energy environments

Most of the observable matter in the Universe is in the form of plasma, or tenuous ionized gas, and the complicated behavior of plasmas underlies many processes in astrophysics. Plasmas interact with electromagnetic fields, display collective effects and instabilities, and can, under certain conditions, accelerate particles far out of thermal equilibrium. Plasmas are also responsible for dissipation of energy, transport, and turbulent properties of many astrophysical flows. While intrinsically microscopic, plasma processes often couple small and large spatial scales and have a way of introducing nonlinear feedback mechanisms into astrophysical systems. This behavior makes it challenging to understand and simulate such plasmas, often requiring kinetic and multiscale methods. I will discuss the state of numerical studies of plasma astrophysical processes, such as shock acceleration and reconnection, and their applications to astrophysical phenomena in gamma-ray bursts, supernova remnants, and neutron star magnetospheres.

Speaker: Anatoly Spitkovsky (Princeton University)

Shanghai_Texas_AS_2023_comprs.pdf

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 12:30 PM Plenary Talk: 10:50, Wednesday

Convener: Prof. Shuang-Nan Zhang (Institute of High Energy Physics)

10:50 AM Cosmic-Ray Super-PeVatron and Other Discoveries by LHAASO

A gigantic bubble of γ-rays with energies up to 2 PeV is detected by LHAASO in the Cygnus region. It implies the existence of a CR accelerator in the core of the bubble which is continuously injecting CR particles with energies up to few tens of PeV in the ambient HI gas thus emitting the UHE photons. This evidences the galactic origin of CRs above the knee which concentrate towards the core and diffuse out over a range of at least 150 pc. The accelerator(s) has yet been identified in the core which has a very complicated morphological structure with several possible UHE photon emitters. The young massive star cluster OB2 is the most favorable candidate of the Super-PeVatron.

Speaker: Prof. zhen cao (中国科学院高能物理研究所)

1-ZhenCao-Cygnus-TEXAS-2023.pdf

11:40 AM Particle acceleration: theory versus observations

Over the recent years, we have witnessed several extraordinary findings in Astrophysics - amongst them the discovery of Ultra High Energy gamma-ray sources, the astronomical objects whose electromagnetic spectra extend beyond 100 TeV. We believe that the discovery of UHE gamma rays should allow us to finally solve the century-old puzzle of the origin of galactic cosmic rays. But the significance of the discovery goes beyond that specific issue. The detection of $\geq 100$ TeV photons implies the existence of particle accelerators boosting the energy of electrons and protons out of 1 PeV, the so-called PeVatrons. The galactic PeVatrons have been detected in diverse forms - Pulsar Wind Nebulae, Massive Stellar Cluster, SNRs, Microquasars, etc. These discoveries confirm some early phenomenological predictions, but, more importantly, they reveal serious challenges for the current theories of particle acceleration in the Milky Way. I will briefly highlight the recent observations and discuss their implications for the Cosmic Ray Factories in the Milky Way.

Speaker: Prof. Felix Aharonian

2-Aharonian-TEXAS2023.pdf

12:30 PM → 1:40 PM Lunch Provided

1:40 PM → 3:20 PM Accretion Processes: 13:30, Wednesday

Conveners: Xinwu Cao (Zhejiang University), Prof. Yosuke Mizuno (TDLI / Shanghai Jiao Tong University)

1:40 PM The EHT tale of two black hole images: recent results and future prospects

Imaging nearby supermassive black holes provides a new astrophysical laboratory, allowing us to test general relativity in the extremely strong gravitational field around black holes and to study physical processes such as mass accretion and jet formation. (Sub)millimeter Very Long Baseline Interferometry (VLBI) observations can achieve the highest spatial resolution in current astronomical observations. In recent years, global (sub)millimeter VLBI, represented by the Event Horizon Telescope (EHT), has made unprecedented progress in black hole imaging and has captured the first images of two nearby supermassive black holes. In this talk, I will present recent results obtained with the EHT and discuss future prospects.

Speaker: Rusen Lu (Shanghai Astronomical Observatory, CAS)

1-Lu_2023-12-13.pdf

2:05 PM Flares and ejections from black hole accretion flows

Flares and ejections are often observed from black holes. One typical example is Sgr A, the supermassive black hole in our Galactic center. In this talk, I will first review our observational results and theoretical understanding of the flares in Sgr A. Special attention will be paid to introduction of high-resolution VLT-GRAVITY results. Then I will focus on the interpretation of these results by our `coronal-mass-ejection' model, which invokes the formation of magnetic flux ropes and their subsequent ejection due to magnetic reconnection. I will introduce the basic physical picture, our 3D GRMHD simulations of accretion flow, the radiative transfer calculations of flares, and our explanations to the GRAVITY results, including light curves, trajectory and the super-Keplerian motion of the hot spots observed by GRAVITY.

Speaker: Feng Yuan (Shanghai Astronomical Observatory)

2:30 PM Magnetic Flux Rope and the Flares in Sgr A∗ from 3D Two-Temperature GRMHD Simulations

Sgr A$^*$ exhibits flares at various wavelengths, but their origin remains unclear. Magnetic flux ropes emerging from the black hole are one of the possible candidates for explaining the observed flares. Based on 3D two-temperature GRMHD simulations of magnetized accretion flows with multi-loop magnetic loops, we calculate the non-thermal emissions from the magnetic flux ropes using a kappa non-thermal electron distribution function (eDF). In kappa eDF, we use a variable kappa sub-grid model based on turbulent and magnetic reconnection acceleration scenarios. In a variable kappa model based on the turbulent acceleration scenario, we can reproduce the observation of near-infrared flares and broadband spectral energy distribution (SED) from the non-thermal emission from the magnetic flux ropes. In the flux variability, we also found an ~30 minute time lag between the near-infrared and submillimeter flares which agrees with observation well.

Speaker: Mr Hongxuan Jiang (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

3-HongxuanJiang_Texas.pdf

2:42 PM Supercritical accretion onto compact objects and massive disk winds

Most ultraluminous X-ray sources (ULXs) may be powered by supercritical accretion onto stellar mass compact objects. In these cases, massive winds is expected to launch due to strong radiation pressure and produce shock-ionized bubble nebulae when interacting with the interstellar medium. I will discuss how to the disk winds shape the observed energy spectrum of ULXs, what one can learn about the accretion physics and evolutionary history of ULXs via VLT MUSE observations of the bubble nebulae, and implications of the ULX feedback in the context of galactic evolution.

Speaker: Prof. Hua Feng (Tsinghua University)

4-HuaFeng_supercritical_texas.pdf

3:02 PM Modeling the inner part of the jet in M87: confronting jet morphology with theory

The formation of jets in black hole accretion systems is a long-standing problem. It has been proposed that a jet can be formed by extracting the rotation energy of the black hole (“BZ-jet”) or the accretion flow (“disk-jet”). While both models can produce collimated relativistic outflows, neither has successfully explained the observed jet morphology. By employing general relativistic magnetohydrodynamic simulations, and considering nonthermal electrons accelerated by magnetic reconnection that is likely driven by magnetic eruption in the underlying accretion flow, we obtain images by radiative transfer calculations and compared them to millimeter observations of the jet in M87. We find that the BZ-jet originating from a magnetically arrested disk around a high-spin black hole can well reproduce the jet morphology, including its width and limb-brightening feature.

Speaker: Hai Yang (SHAO)

5-HaiYang-Texas.pdf

1:40 PM → 3:20 PM Astroparticle: 13:30, Wednesday

Convener: Gwenael Giacinti (TDLI & SJTU)

1:40 PM Toward an understanding of Galactic PeVatrons

The existence of a “knee” at a few PeV in the cosmic-ray spectrum suggests the presence of Galactic PeV proton accelerators called “PeVatrons.” The search for PeVatrons has been significantly advanced lately, thanks to the launches and operation of very-high-energy gamma-ray and high-energy neutrino observatories. This talk will present the latest observations of a few candidate PeVatrons. We will discuss how the new observations of both individual sources and the diffuse emission of the Galactic Plane improve our understanding of Galactic PeVatrons and their implications for future astroparticle studies at TeV-PeV energies.

Speaker: Ke Fang

1_Texas_KeFang.pdf

2:05 PM Transport of relativistic particles observed in the parsec-scale jets of SS 433

The microquasar system SS 433 provides a unique opportunity to study mildly relativistic collimated jets in our own Galaxy. While much is known about the nature of the precessing inner jets, the dynamics at large distances from the central binary system are poorly constrained. The abrupt reappearance of non-thermal x-ray synchrotron emission at around 25 parsecs either side of the core indicates the presence of a site of strong energy dissipation, though its origin and role in the jet dynamics cannot be uniquely determined through the synchrotron emission alone. In this talk, I will report on recent observations of this system by several very-high-energy gamma-ray instruments, which directly trace the inverse-Compton emission arising from the energetic electron population. These observations, in particular the H.E.S.S. discovery of energy- dependent morphology in the gamma-ray emission from the jets, establish the location of one of the most effective particle accelerators in the Galaxy and constrain the dynamics of the parsec-scale jets. The findings concerning particle acceleration in the jets of SS 433 can then be extrapolated to other sources hosting powerful relativistic jets which are too distant for their gamma-ray emission to be spatially resolved by the current generation of telescopes.

Speaker: Laura Olivera-Nieto (Max Planck Institut für Kernphysik)

2:30 PM High-energy non-thermal emission from local young massive stellar clusters

Cosmic ray acceleration up to PeV energies has been suggested to take place in massive and young stellar clusters. The formation of a strong termination shock driven by the collective action of stellar winds in a compact cluster offers a promising location where efficient particle acceleration might take place. The subsequent interactions of these particles with target gas result into hadronic gamma-ray and neutrino production: in particular, if dense clouds are located within and around clusters, enhanced emission is expected. Within a scenario of particle acceleration at the cluster wind termination shock, we compute the emerging multi-messenger signals from local star clusters observed by Gaia, as well as from the nearby illuminated molecular clouds reported in Miville-Deschenes catalog. We further evaluate detection prospects of these signals.

Speaker: Silvia Celli (Sapienza Università di Roma)

2:42 PM Galactic Black Holes as PeVatrons and sub-PeV gamma-ray sources

Our Galaxy is filled with cosmic rays, but the origin of PeV cosmic rays have been unknown for a long time. Recently, LHAASO discovered mysterious sub-PeV gamma-ray sources without any obvious counterparts in other wavelengths, and origins of these gamma-ray sources are also unknown. In this talk, we propose that isolated stellar-mass black holes (IBHs) wandering in molecular clouds can be the source of PeV cosmic rays and un-ID LHAASO sources. The accretion flow onto black holes can be magnetically arrested disks (MADs), where magnetic reconnection can accelerate high-energy particles via magnetic reconnection. We show that MADs around IBHs can accelerate cosmic-ray protons up to PeV energies and their production rate can be consistent with the PeV cosmic rays observed on Earth. These PeV cosmic rays interact with gas in molecular clouds, and we should see sub-PeV gamma-rays from molecular clouds where IBHs are embedded. This scenario can explain the hard spectral feature in TeV bands seen in some LHAASO unidentified sources.

Speaker: Shigeo Kimura (Tohoku University)

4_Kimura_GalacticBHasPeVatron.pdf

3:07 PM Origin and Cosmic Ray Acceleration in Fermi Bubbles and Other High Energy Phenomena at the Galactic Center

The center of our Milky Way galaxy hosts a series of energetic outbursts, including the well-known Fermi and eROSITA bubbles, galactic center lobes, the inner 15-pc X-ray lobes. Are they long-lasting or fast evolving explosive events? What causes these structures? Are they PeVatrons related to ultra high energy gamma ray emissions from the central molecular zone and the Galactic center? The Fermi and eROSITA bubbles may correspond to typical galactic feedback processes occurring in our own Galaxy in the near past. Galactic feedback is one central unsolved problem in contemporary astronomy, and the Fermi and eROSITA bubbles are also galactic-scale accelerators of cosmic rays, whose origin remains a century-long mystery. In this talk, I will describe our long journey to reveal the origin of the Fermi bubbles. Our recent jet-shock model could explain the X-ray, gamma-ray, and microwave observations of the Fermi bubbles, suggesting that they were produced by a pair of powerful jets emanating from the supermassive black hole at the Galactic center about 5 million years ago. We also use a similar jet-shock model to explain the origin of the inner 15-pc X-ray lobes, which may be related to ultra high energy gamma ray emissions from the central molecular zone.

Speaker: Fulai Guo (Shanghai Astronomical Observatory, Chinese Academy of Sciences)

5_texasinshanghai23_guo.pdf

1:40 PM → 3:20 PM Cosmic Explosions...: Wednesday

Convener: Wenbin Lu (UC Berkeley)

1:40 PM Tidal Disruption Events: Unique probes of outflows and accretion in supermassive black holes

Supermassive black holes (SMBHs) lie at the centers of most galaxies, but the processes by which they grow and launch outflows that shape the galaxies around them remain poorly understood. In this talk, I will focus on tidal disruption events (TDEs) as probes of relativistic processes powered by SMBHs. A TDE occurs when a star passes too close to a SMBH and is torn apart by tidal forces from the strong gravitational field, injecting a large amount of gas close to the event horizon. TDEs therefore provide a valuable opportunity to test theories of SMBH accretion and to study the formation and growth of relativistic jets and outflows. Mass ejection in TDEs is best characterized via radio observations, which reveal synchrotron radiation produced in the shock formed between fast-moving outflows and the ambient interstellar medium. Radio observations of TDEs allow us to (1) determine the properties of outflowing material (energy, size, expansion velocity) and (2) trace the ambient density profile around previously-dormant SMBHs on scales of a few light years. I will discuss exciting ongoing observations of TDEs in the local Universe, which reveal an unexpectedly diverse population. The increased sample size now being realized by wide-field surveys has enabled the first constraints on the prevalence of radio emission in TDEs weeks to years post-disruption, which will shed further light on the physical conditions required for jet and outflow formation.

Speaker: Kate Alexander (University of Arizona)

1-KDA_Texas.pdf

2:05 PM Tidal Disruption Events: Probes of Accretion Physics and Black Hole Demographics

Tidal disruption events (TDEs) provide unique laboratories to study the demographics, immediate stellar and gaseous environments, and accretion physics of the massive black hole population. Over the past few years, time domain sky surveys such as the optical Zwicky Transient Facility (ZTF) have led to a surge of TDE discoveries in galaxy centers. I will present how detailed X-ray studies of two ZTF-discovered TDEs (AT2021ehb and AT2022cmc) have revealed the evolving inflow and outflow properties across different regimes of accretion. I will also summarize our efforts to constrain the TDE luminosity function and the shape of the local black hole mass function using a complete flux-limited ZTF TDE sample.

Speaker: Yuhan Yao (University of California, Berkeley)

2-YuhanYao_20231213_texas.pdf

2:25 PM Tidal Disruption Events: Demographics, Accretion and Outflows

Tidal disruption event is a unique probe of quiescent massive black holes. In this talk, I will discuss how we can use tidal disruption events to constrain the demographics of massive black holes including intermediate mass black holes. I will also show our recent theoretical modelling results on the accretion, outflow and emission processes in tidal disruption events, which can be used to explain various observed signatures.

Speaker: Prof. Jane Dai (The University of Hong Kong)

3-Dai_TexasSymposium2023.pdf

2:45 PM Probing Intermediate-Mass Black Holes with Tidal Disruption Events

The study of intermediate-mass black holes (IMBHs) has recently drawn a lot of attention, since IMBHs can provide critical information on the seed formation process of supermassive black holes (SMBHs) along with the co-evolution of massive black holes (MBHs) and galaxies. However, detecting IMBHs is extremely difficult due to their small masses and dim luminosities. One of the most promising methods for detecting IMBHs is through tidal disruption events (TDEs), in which stars are tidally disrupted by the MBHs.

In this work, for the first time, we calculate the rates of TDEs using the realistic stellar profiles of galaxies and stellar clusters hosting IMBHs. We select a sample of galaxies and stellar clusters, which not only host IMBHs in their nuclei but also have the IMBH masses constrained from dynamical measurements. We then perform a sophisticated loss-cone dynamics calculation and obtain the TDE rates from this sample of IMBHs. We find that TDE rate generally increases with increasing black hole mass in the IMBH regime, which is opposite to the trend found for SMBHs. Moreover, we show that IMBH TDEs produce deeply plunging orbits more frequently than SMBH TDEs. These results are crucial for helping us use TDEs to probe IMBHs and design next-generation transient telescopes.

Speaker: Janet Chang (HKU)

4-Janet_IMBH_TDE_Presentation.pdf

2:55 PM A holistic view of compact binary mergers: from kilonova to afterglow

Compact binary mergers serve as excellent astrophysical laboratories to explore a wide range of fundamental problems: from the formation of ultrafast outflows to the cosmic production of heavy metals, from the equation of state of cold ultra-dense matter to the expansion rate of the universe.
Our understanding of these systems was revolutionized in 2017 by the discovery of the first merger of two neutron stars (NSs), GW170817, followed by the kilonova AT2017gfo and a long-lasting X-ray afterglow. In this talk I will discuss the most recent advances in kilonova and afterglow studies driven by observations of gravitational wave sources and gamma-ray bursts.

Speaker: Prof. ELEONORA TROJA (UNIVERSITY OF ROME)

TEXAS_2023_Troja.pdf

1:40 PM → 3:20 PM Plasma Astrophysics: 13:30, Wednesday

Convener: Zhengming Sheng (Shanghai Jiao Tong University)

1:40 PM Energy partition in high Mach number collisionless shocks

Astrophysical shock waves are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar or intergalactic medium, shocks are inferred to heat the plasma, amplify magnetic fields, and accelerate electrons and protons to highly relativistic speeds. However, the exact mechanisms that control energy partition in shocks remain a mystery. This is particularly challenging for high Mach number shocks, such as those associated with supernova remnants, where spacecraft data in the relevant regime is scarce and the shock structure cannot be directly resolved from observations. I will discuss recent progress in using the combination of fully kinetic simulations and laser-driven laboratory experiments to study energy partition in high-Mach number collisionless shocks. In particular, I will discuss results on magnetic field amplification, plasma heating and particle acceleration, and how experimental measurements are helping benchmark models of the shock microphysics.

Speaker: Frederico Fiuza (Instituto Superior Técnico)

Wed1_Fiuza.pdf

2:05 PM Relativistic electron injection acceleration in laser-driven magnetic reconnection plasmas

Magnetic reconnection (MR) is a fundamental plasma process in which regions of oppositely directed magnetic field merge, leading to the conversion of magnetic energy into high speed flows, thermal energy and accelerating particles. Acceleration of particles during MR has become a hot topic in recent years. However what, where and how those accelerated particles are generated are still not well understood. Here we report, using a millimeter plasma device, that, successfully forming a low $\beta$ $\sim$ 0.03 (the ratio between the thermal pressure and the magnetic pressure) MR, significant non-thermal electrons are generated, which shows a typical power law and the spectral indices is $\sim$ 1.17 much flatter than those of laser driven high $\beta$ MR. We also firstly obtained a Gaussian-like MeV electron bump at high energy tail. Combining the experimental results on optical shadows, X-ray self-emissions, and proton radiographs, together with simulations, the process of electron acceleration during MR is clearly described and shows potential applications in development of electron accelerator with optional energy and understanding of the strong particle energization in solar flares and accretion disk coronae et al.

Speaker: Mr Jiayong Zhong (Beijing Normal University)

Wed2_jiayongzhong.pdf

2:30 PM Upper Field-strength Limit of Fast Radio Bursts

Fast radio bursts (FRBs) are cosmological radio transients with an unclear generation mechanism. Known characteristics such as their luminosity, duration, spectrum, and repetition rate, etc., suggest that FRBs are powerful coherent radio signals at GHz frequencies, but the status of FRBs near the source remains unknown. As an extreme astronomical event, FRBs should be accompanied by energy-comparable or even more powerful X/γ-ray counterparts. Here, QED particle-in-cell simulations of ultrastrong GHz radio pulse interaction with GeV photons show that at 3e12V/cm field strengths, quantum cascade can generate dense pair plasmas, which greatly dampen the radio pulse. Thus, in the presence of GeV photons in the source region, GHz radio pulses stronger than 3e12V/cm cannot escape. This result indicates an upper field-strength limit of FRBs at the source.

Speaker: Prof. Hui-Chun Wu (Zhejiang University)

2:55 PM Towards a unified picture of energy partition in high Alfvén Mach number collisionless shocks

Collisionless shock waves shape the nonthermal emission in a wide range of environments, including modern laboratory experiments and astrophysical outflows. In weakly magnetized plasma flows, self-generated nonlinear electromagnetic plasma processes are inferred to heat and accelerate electrons and ions. Understanding the mechanisms that underpin the energy transfer between plasma species and the downstream temperature ratio between electrons and ions constitutes a fundamental challenge in modeling such blast waves. In this presentation, I will outline recent efforts to model the transport of electrons in Weibel-mediated shocks. I will introduce a new model accounting for electron heating in an ambipolar-type process through the interplay between pitch-angle scattering in the microturbulence and the coherent electrostatic field induced by the difference in inertia between species. Via analytical kinetic and fluid estimates, a semi-analytical Monte Carlo-Poisson method, and large-scale ab-initio Particle-In-Cell simulations, I will discuss the electron-ion energy partition in the downstream of high Alfvén Mach numbers shocks relevant to supernova remnants and laboratory experiments. I will then present the extension of this model to the relativistic regime to demonstrate equipartition inferred from the afterglow emission of gamma-ray bursts. Finally, I will explore the implications of this model on electron injection in nonthermal distributions.

Speaker: Arno Vanthieghem (Princeton University/NINS)

Wed4_Vanthieghem.pdf

3:07 PM Electromagnetic fireworks from erupting magnetars

Highly magnetized neutron stars are a source of extreme transients observed in different bands, like the fast radio burst (FRB) and associated hard X-ray burst from the Galactic magnetar SGR 1935+2154. The origin of such outbursts, hard X-rays on the one hand and millisecond duration FRBs on the other hand, is still unknown. We present a global model for various kinds of such magnetar outbursting activities. Crustal surface motions can twist the inner magnetar magnetosphere by shifting the frozen-in footpoints of magnetic field lines. We discuss criteria for various instabilities of 3D twisted flux bundles in the force-free dipolar magnetospheres and compare their energetic properties to observations of magnetar X-ray flares. We then connect such activities to recently developed FRB generation mechanisms in the outer magnetosphere of a magnetar. In a reconnection-mediated model, a magnetic pulse induced by a magnetar flare collides with the current sheet of the magnetar wind, compresses, and fragments it into a self-similar chain of magnetic islands. Time-dependent plasma currents created during their collisions produce relatively narrow-band GHz emission with luminosities sufficient to explain bright extragalactic FRBs. Alternatively, a so far unexplored shock-mediated FRB mechanism can convert magnetic perturbations of the magnetar wind to radio waves.

Speaker: Jens Mahlmann (Columbia University)

Wed5_Mahlmann.pdf

3:20 PM → 3:30 PM Poster: Poster Viewing

3:30 PM → 4:30 PM 3:30 Bus leaves for TDLI

4:30 PM → 5:30 PM Reception at TDLI

5:30 PM → 7:00 PM 5:30 Bus goes to dinner place

7:00 PM → 9:00 PM Dinner / Cruise

9:00 PM → 10:00 PM Bus leaves for hotels

Thursday, December 14

8:40 AM → 10:20 AM Plenary Talk: Thursday

Convener: Prof. Pengjie Zhang (Shanghai Jiao-Tong University)

8:40 AM Cosmic Structure and the Nature of Dark Matter

Nonlinear cosmic structure grew through gravity acting on small fluctuations that emerged from the early universe and are observed directly in the microwave background radiation. It thus depends on the law of gravity, on the nature of the gravitating matter and on the process that generated the initial fluctuations. Weakly interacting dark matter appears to dominate the material content of the Universe at all observable times. Nonlinear structure formation on both very large and very small scales is affected by the particle physics of dark matter, and determines its detectability through annihilation radiation. It is very difficult to account for the full range of phenomena in which Dark Matter appears to play a dominant role through a modification of the Law of Gravity.

Speaker: Simon White

White_TexasShanghai23.pdf

9:30 AM Cosmology with large-scale structure

The nature of the main ingredients of the standard model of cosmology, dark matter and dark energy, remains a mystery. Better observations are needed, where the biggest advance will come from precise measurements of the growth of large-scale structure. In principle, the next generation of imaging and spectroscopic surveys provide an impressive amount of information about the universe, but extracting this information is challenging: a wide range of observational and astrophysical complications prevent a direct, simple interpretation. To fully exploit the potential of these data, we need to improve our understanding of how galaxies populate dark matter halos. I will make the case that this is possible.

Speaker: Henk Hoekstra (Leiden University)

Henk-texasshanghai.pdf

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 12:30 PM Plenary Talk: Thursday

Convener: Prof. Xiaohu Yang (Tsung-Dao Lee Institute, SJTU)

10:50 AM Dark matter laboratory search overview

The nature of dark matter stands as one of the most fundamental mysteries in physics. Numerous theories beyond the Standard Model have postulated the existence of dark matter particles. However, despite extensive research, compelling laboratory evidence has yet to be obtained. In this presentation, I will provide an overview of the global experimental endeavors dedicated to the search for dark matter particles, and briefly discuss future prospects and potential directions.

Speaker: Jianglai Liu (Shanghai Jiao Tong University)

1-Status-DM-texas-symp1214-submit.pdf

11:40 AM A minimal SM/LCDM cosmology

Title: A minimal SM/LCDM cosmology
Neil Turok, University of Edinburgh and Perimeter Institute
Abstract:
Recent observations point to a surprisingly economical description of the universe on both very small and very large scales. Stimulated by these findings, Boyle and I have proposed a new, potentially more complete theoretical framework than currently popular paradigms. Our search has so far led to 1) the simplest-yet explanation for the cosmic dark matter, soon to be tested by galaxy surveys, 2) a thermodynamic explanation for the large scale geometry of the cosmos, based on the concept of gravitational entropy à la Hawking, 3) a new account of the big bang singularity as a “mirror” enforcing CPT-symmetric boundary conditions, realising Penrose's ``Weyl curvature hypothesis" and 4) a new mechanism for cancelling the divergent vacuum energy and the trace anomalies in the Standard Model (SM). The new mechanism successfully predicts the primordial density perturbations in terms of the SM’s gauge couplings. It also explains why there are 3 generations of elementary particles, each including a RH neutrino, one of which is stable and comprises the dark matter. I’ll outline the challenges the new picture faces and the opportunities it presents including prospective observational tests.

Speaker: Neil Turok (University of Edinburgh, UK)

2-ShanghaiTurokSlidesFinal.pdf

12:30 PM → 1:40 PM Lunch (on your own)

1:40 PM → 3:20 PM Cosmology with large-scale structure: Thursday

Convener: Jiaxin Han (Shanghai Jiao Tong University)

1:40 PM Subaru Hyper Suprime-Cam Year 3 Cosmology Results: S8 tension?

We used more than 25 million galaxies in the Subaru Hyper Suprime-Cam (HSC) shear catalog in the redshift range up to z~1.5 to measure weak lensing distortion effects due to large-scale structures. We used the measured weak lensing signals to perform a blinded cosmology analysis to measure the cosmological parameters of the flat LambdaCDM model. To obtain a robust constraint on the cosmological parameters, we employed a uninformative flat prior to model a possible residual systematic error in the mean redshift for HSC galaxies at z>1. As a result, we were able to measure the “S8” parameter at a 4% accuracy (sigma(S8)~0.04), but the central value exhibits about 2.5sigma tension with the Planck inferred S8 value. Our results indicate a non-zero residual error in the mean source redshift compared to the photometric redshift estimates for the HSC galaxies at z>1. In this talk, I will discuss the HSC cosmology results, and, if time is allowed, present the current status of the upcoming Subaru Prime Focus Spectrograph project, which promises significantly improvement of the HSC cosmology results.

Speaker: Prof. Masahiro Takada (IPMU)

2:00 PM Overview and Latest Progress of the Dark Energy Spectroscopic Instrument (DESI)

The Dark Energy Spectroscopic Instrument (DESI) will obtain optical spectra for approximately 40 million galaxies and quasars. Using the three-dimensional distribution of these galaxies, DESI aims to measure the universe's expansion history over the past 11 billion years, thereby exploring physics of dark energy. In this talk, I will provide an overview of the DESI survey along with its latest updates. I will cover topics including the early data release, the current status of the survey, various ongoing science projects, and potential future programs within DESI. Additionally, I will discuss the planned analyses employing higher-order statistics within the DESI collaboration

Speaker: Jiamin Hou (Max Planck Institute for Extraterrestrial Physics)

2:20 PM An Overview of the Chinese Space Station Telescope

The 2m-aperture Chinese Space Station Telescope (CSST) is a major science project of China Manned Space Program. It is planned to launch in 2025 and has a nominal mission lifetime of 10 years. During observations, the CSST will fly independently at a large distance from the space station. It can dock with the space station for servicing as scheduled or as needed. With a Cook-type three-mirror anastigmat design, the CSST can achieve superior image quality within a large field of view (FoV), which gives it an advantage for survey observations.

The CSST will be equipped with 5 first-generation instruments including a Survey Camera, a Terahertz Receiver, a Multichannel Imager, an Integral Field Spectrograph, and a Cool Planet Imaging Coronagraph. Its primary task is to carry out a high-resolution large-area multiband imaging and slitless spectroscopy survey covering the wavelength range of 255 nm to 1000 nm. It will take the Survey Camera roughly 7 years of operation accumulated over 10 years of orbital time to image roughly 17,500 square degrees of the sky in NUV, u, g, r, i, z, and y bands and take slitless spectroscopy of the same sky in 3 bands. The point-source 5σ limiting magnitudes in g and r bands can reach 26 (AB mag) or higher. The spectral resolution (R=λ/Δλ) of the slitless spectrograph is specified to be on average no less than 200, and the wide-band-equivalent limiting magnitudes in GV (400-620 nm) and GI (620-1000 nm) bands will be 23 or higher. Deep fields will be selected for more observations to reach at least one magnitude deeper than the wide-area survey. In this talk, I will give an overview of the project and discuss its potential for cosmological studies.

Speaker: Hu Zhan (NAOC)

CSST20231214.pdf

2:40 PM Is the large-scale structure traced by the BOSS LOWZ galaxies consistent with Planck?

Recently, several studies reported a significant discrepancy between the clustering and lensing of the Baryon Oscillation Spectroscopic Survey (BOSS) galaxies in the Planck cosmology. We construct a simple yet powerful model based on the linear theory to assess whether this discrepancy points toward deviations from Planck. Focusing on scales $10{<}R{<}30\,h^{-1}\mathrm{Mpc}$, we model the amplitudes of clustering and lensing of BOSS LOWZ galaxies using three parameters: galaxy bias $b_\mathrm{g}$, galaxy-matter cross-correlation coefficient $r_\mathrm{gm}$, and $A$, defined as the ratio between the true and Planck values of $\sigma_8$. Using the cross-correlation matrix as a diagnostic, we detect systematic uncertainties that drive spurious correlations among the low-mass galaxies. After building a clean LOWZ sample with $r_\mathrm{gm}{\sim}1$, we derive a joint constraint of $b_\mathrm{g}$ and $A$ from clustering+lensing, yielding $b_\mathrm{g}{=}2.47_{-0.30}^{+0.36}$ and $A{=}0.81_{-0.09}^{+0.10}$, i.e., a $2\sigma$ tension with Planck. However, due to the strong degeneracy between $b_\mathrm{g}$ and $A$, systematic uncertainties in $b_\mathrm{g}$ could masquerade as a tension with $A{=}1$. To ascertain this possibility, we develop a new method to measure $b_\mathrm{g}$ from the cluster-galaxy cross-correlation and cluster weak lensing using an overlapping cluster sample. By applying the independent bias measurement ($b_\mathrm{g}{=}1.76{\pm}0.22$) as a prior, we successfully break the degeneracy and derive stringent constraints of $b_\mathrm{g}{=}2.02_{-0.15}^{+0.16}$ and $A{=}0.96{\pm}{0.07}$. Therefore, our result suggests that the large-scale clustering and lensing of LOWZ galaxies are consistent with Planck, while the different bias estimates may be related to some observational systematics that needs to be mitigated in future surveys.

Speaker: Zhiwei Shao (Shanghai Jiao Tong University)

4_ZhiweiShao_Texas_LOWZBias.pptx

2:50 PM Evaluating baryonic effects in HSC Y3 cosmic shear data with a dark matter-only model

Cosmic shear is a powerful tool for revealing matter distribution in the large-scale structure of the universe. Li et al. (2023) and Dalal et al. (2023) measured the tomographic cosmic shear correlation functions and power spectra, respectively, from the HSC-Y3 data, and then constrained the cosmological parameters from the model fitting. Although the small scale data has a high signal-to-noise ratio, accurately modeling matter distribution on these scales is still challenging due to poorly understood baryonic effects. These baryonic effects have garnered attention as potential contributors to alleviating the $S_8$ tension observed between weak-lensing cosmology and the cosmology inferred from Planck data. Consequently, there is a growing trend to model these baryonic effects based on hydrodynamical simulations and to account for the uncertainty by marginalizing over the associated baryonic physics parameters.
The problem is, however, that there are still uncertainties in the subgrid physics of baryonic effects employed in cosmological hydrodynamical simulations. As an alternative to pursuing an accurate or flexible baryonic physics model, our approach involves assessing the performance of a dark matter (DM)-only model prediction. Due to advancements in cosmological simulations, DM-only model predictions for the large-scale structure are considered an accurate theoretical model, next to the linear theory of structure formation. We evaluate the goodness-of-fit of DM-only model predictions and find that this model can fit the cosmic shear correlation functions measured from the HSC-Y3 data, even at scales below the fiducial scale cuts. This finding suggests that no significant baryonic effects are present in the HSC-Y3 cosmic shear data, considering its associated uncertainties.

Speaker: Ryo Terasawa (Kavli IPMU)

32ndTexas_Ryo_Terasawa.pdf

3:00 PM Photometric BAO measurements with DES

We present the Baryonic Acoustic Oscillations (BAO) measurements using the First Three Year data from the Dark Energy Survey (DES). We describe the data sample and the mock catalog used for BAO measurements. In addition to the tomographic analysis results, I will also present the alternative projective 3D correlation function analysis. The DES Y3 BAO measurement gives the most precise BAO constraint from photometric data. I will also mention some of the ongoing DES Y6 BAO measurement results. Finally, I discuss the possibility of reconstructing the photometric BAO signals.

Speaker: Kwan Chuen Chan (Sun-Yat Sen University)

6_KwanChuenChan_BAODES.pdf

3:10 PM The hybrid RSD model: 1-template and emulators

I will present the details of the hybrid RSD model, which combines PT with N-body simulations. 1-template and emulator versions of the model will be presented.

Speaker: Dr Yi Zheng (SYSU)

YiZheng_231214_Texas_Symposium_talk_Shanghai_short.pdf

1:40 PM → 3:20 PM GW Astrophysics: 14:00, Thursday

1:40 PM Extreme Mass Ratio Inspirals: Formation, Dynamics and Astrophysical Applications

In this talk I will discuss one of the primary targets of space-borne gravitational wave detectors – the Extreme Mass Ratio Inspirals, which usually comprises a massive black hole and a stellar-mass companion. In recent years there are significant progress in terms of its formation channel, rate estimation and dynamics in astrophysical environments. I will review these new developments and then discuss the significance of detecting these sources with gravitational waves and possibly electromagnetic counterparts.

Speaker: Huan Yang (Perimeter Institute & University of Guelph)

1-Talk_Huan.pptx

2:00 PM Electromagnetic emission from merging black hole binaries

The LIGO experiment has detected mergers between stellar-mass black
holes, and pulsar timing arrays on the ground have discovered a
stochastic background of gravitational waves attributable to merging
massive black hole binaries. The LISA satellites, planned in space in
the mid 2030s, are expected to detect gravitational waves (GWs) from
individual massive black hole binaries at high signal-to-noise. These
black hole mergers should often take place in gas-rich galactic
nuclei, and therefore should also produce concurrent electromagnetic
(EM) emission.

In this talk, I will highlight the importance of these black hole
mergers for astrophysics, cosmology, and fundamental physics, and
emphasize the additional science potential of joint GW and EM
detections. I will then discuss our recent work on the coupled
dynamics of a BH binary with circumbinary gas, focusing on the
expected characteristics of the EM emission from such a system.
I will present BH binary candidates based on these signatures, and
discuss the challenges and future work needed to confirm these
binaries and to realize their science potential.

Speaker: Zoltan Haiman (Columbia University)

2-HaimanZoltan.pptx

2:20 PM 3D Dynamics of Embedded Stellar-Mass Binary Black Holes within AGN Disks and their Feedback Effects

The GW190521 event – an 85 Msun and a 66 Msun black hole (BH) coalescing to a 142 Msun BH – the heaviest binary black hole (BBH) merger to date has opened up new discussions on the formation channels of BBHs as possible LIGO sources. In this talk, we focus on the scenario where BBHs are embedded inside an AGN disk (disk around a supermassive black hole at the center of a galaxy). We will present high-resolution 3D simulations of stellar mass black hole binaries to examine the physical processes that regulate their orbital evolution. We demonstrate that there is a hierarchy of disk structures in such an embedded BBH, which is important in regulating the angular momentum evolution. Furthermore, we investigate how the jets from BHs could impact their surrounding environment, modifying their accretion flow and accretion rates. Implications for possible observational signatures will be discussed as well.

Speaker: Prof. Hui Li (Los Alamos)

3-.pptx

2:40 PM Superradiant clouds in binaries

Bosonic particles within a suitable mass range may form clouds around rotating black holes through the black hole superradiance process. For black holes in binary black hole systems, it has been suggested that these clouds are mostly depleted at large binary separations because of a resonant level mixing effect, and hence may not be dynamically relevant for black hole and neutron star binaries that enter the LIGO and LISA detection frequency band. In this talk, we discuss the possibility that the common envelope process during a compact binary evolution may protect the clouds from the depletion. When the binary separation further decreases due to gravitational wave radiation, we discuss the impact of non-resonant level mixing for cloud depletion, as well as possible cloud mass transfer between the binary objects. We also comment on the state of the cloud after the binary enters the frequency band of ground-based detectors.

Speaker: Jun Zhang (International Center for Theoretical Physics Asia-Pacific)

2:50 PM Disappearing thermal X-ray emission as a tell-tale signature of merging massive black hole binaries

The upcoming Laser Interferometer Space Antenna (LISA) is expected to detect gravitational waves (GWs) from massive black hole binaries (MBHB). Finding the electromagnetic (EM) counterparts for these GW events will be crucial for understanding how and where MBHBs merge, measuring their redshifts, constraining the Hubble constant and the graviton mass, and for other novel science applications. However, due to poor GW sky localisation, multi-wavelength, time-dependent electromagnetic (EM) models are needed to identify the right host galaxy. We studied merging MBHBs embedded in a circumbinary disc (CBD) using high-resolution two-dimensional simulations, with a Γ-law equation of state, incorporating viscous heating, shock heating, and radiative cooling. We simulate the binary from large separation until after merger, allowing us to model the decoupling of the binary from the circumbinary disc. We compute the EM signatures and identify distinct features before, during, and after the merger. Our main result is a multi-band EM signature: we find that the MBHB produces strong thermal X-ray emission until 1-2 days prior to the merger. However, as the binary decouples from the CBD, the X-ray-bright minidiscs rapidly shrink in size, become disrupted, and the accretion rate drops precipitously. As a result, the thermal X-ray luminosity drops by orders of magnitude, and the source remains X-ray dark for several days, regardless of any post-merger effects such as GW recoil or mass loss. Looking for the abrupt spectral change where the thermal X-ray disappears is a tell-tale EM signature of LISA mergers that does not require extensive pre-merger monitoring.

Speaker: Luke Krauth (Columbia University)

4-Krauth_Luke_Texas_2023.pptx

3:00 PM Gravitational Waves from Coalescing Black Hole Binaries in Observed Early Quasar Populations

Gravitational waves (GWs) in the millihertz bands provide are great tools for understanding the cosmological evolution of supermassive black holes (SMBHs) in galactic nuclei. SMBH binaries in high-redshift quasars are expected to be the primarily target of individually identified GW sources. Previous studies mainly considered specific BH seeding models and limited mass ranges in estimating the GW event rate (e.g., light BH seeds originating from Population III remnants vs. heavy BH seeds through direct-collapse of massive pristine gas). Recently, the unprecedented sensitivity of James Webb Space Telescope (JWST) has enabled the discovery of low-mass BHs with masses of 10^6-10^8 Msun at z~4-7, hidden in the pre-JWST era. Combined with known quasars, those newly discovered samples improve understanding of the low-mass end of the BH mass distribution.
In this talk, we present a theoretical model describing BH growth from initial seeding at z>20 to z~2, with an initial seed mass function developed by radiation hydrodynamical simulations, differing from light or heavy seed scenarios. By constraining the model parameters with the up-to-date observed quasar luminosity functions and BH mass functions, we construct the evolution tracks of the BH progenitors. The calibrated model offers a more reliable event rate of GW emission with future space-based GW interferometers, revealing a distinguishable mass distribution for detectable binary BH mergers compared to previous assumptions.

Speaker: Kohei Inayoshi (Peking University)

5-KoheiInayoshi_SH.pdf

3:10 PM Uncovering a hidden black hole binary from secular eccentricity variations of a tertiary star

We study the dynamics of a solar-type star orbiting around a black hole binary (BHB) in a nearly coplanar system. We present a novel effect that can prompt a growth and significant oscillations of the eccentricity of the stellar orbit when the system encounters an “apsidal precession resonance,” where the apsidal precession rate of the outer stellar orbit matches that of the inner BHB. The eccentricity excitation requires the inner binary to have a nonzero eccentricity and unequal masses and can be created even in noncoplanar triples. We show that the secular variability of the stellar orbit’s apocenter, induced by the changing eccentricity, could be potentially detectable by Gaia. Detection is favorable for BHBs emitting gravitational waves in the frequency band of the Laser Interferometer Space Antenna, hence providing a distinctive, multimessenger probe of the existence of stellar-mass BHBs in the Milky Way.

Speaker: Bin Liu (Zhejiang University)

1:40 PM → 3:25 PM High-E Missions...: Thursday

Convener: Shuangnan Zhang

1:40 PM A multi-cubic-kilometer neutrino telescope in the Western Pacific Ocean

IceCube's discovery of an extragalactic neutrino flux has marked the beginning of a new era for neutrino astronomy, prompting the development of more sensitive next-gen neutrino telescopes to uncover the source of cosmic rays and explore physics beyond the Standard Model on cosmic scales. Amid global efforts to build advanced observatories, a telescope near Earth's equator provides unique coverage to the entire neutrino sky. This talk discusses a successful pathfinder experiment identifying a promising site in the Western Pacific Ocean (northern South China Sea) and outlines the TRIDENT neutrino telescope's conceptual design, performance, and timelines.

Speaker: Prof. Donglian Xu (T D Lee Institute)

1_trident_texas2023_dxu.pdf

2:05 PM Polarimetry of GRB prompt emission with POLAR and POLAR-2

Gamma-Ray Burst (GRB) prompt polarization has been measured in more than thirty cases. However, as they suffered from large systematical/statistical uncertainties, they showed a wide range distribution of polarization degrees (PDs). The theoretical community has recently paid more attention to the POLAR mission, which reported PDs of 14 GRBs at mostly a level of $\sim$10% and a hint of polarization angle (PA) evolution over time. If the prompt gamma-rays are produced by photospheric emission, multiple scattering will significantly reduce the PD; synchrotron radiation would also allow a low PD if the magnetic field is dissipated. In another non-uniform jet scenario, if stochastic variations (patchy shells or mini-jets at scales $\ll1/\Gamma$) indeed endure with intrinsically independent magnetic field orientation and evolution, the integrated PD would be suppressed and PA evolution would occur. More realistic theoretical models of both time-/energy-dependent polarization based on advanced numerical simulations are needed to better interpret the results. Meanwhile, the next-generation polarimeter POLAR-2 is required to improve the measurement accuracy. POLAR-2 will be launched in 2025 to the China Space Station and consists of three detectors: a High-energy polarization Detector, a Low-energy polarization Detector and a Broad-band Spectroscopy Detector, sharing most of their mission time to monitor jointly the sky with overlapped fields of view. The synergies of the three detectors will allow POLAR-2 to significantly improve the accuracy ($\sim$10 times better) of GRB polarimetry, and shed new light on the jet physics of GRBs.

Speaker: Hancheng Li (Department of Astronomy, University of Geneva)

2_Polarimetry of GRB prompt emission with POLAR and POLAR-2 (Dec 14 2023 Shanghai).pdf

2:25 PM The Chinese-French SVOM mission

This presentation will provide an overview of the Chinese-French SVOM mission, scheduled for launch in the first half of 2024, which aims to study gamma-ray bursts and other high-energy phenomena. The specific characteristics of the SVOM instruments will be detailed presented and the potential scientific contributions will be discussed.

Speaker: Dr Liping XIN (National Astronomical Observatories, CAS)

3_SVOM-XinLiping-Shanghai-20231214-v2.pdf

2:45 PM UV Explorers for Cosmic Ecosystems in China

For Cosmic Ecosystems, mapping the circumgalactic medium (CGM) in emission is one of the important scientific goals for astronomers to either use the modern ground-based telescopes or the future space missions. CGMs are multi-phases, key to understand the galaxy ecosystem and its accretion and feedback. In this talk, I will briefly introduce a few scientific projects in our group for the efforts in the warm and hot diffuse emission in nearby universe. In addition, I will introduce and summarize the developments of our proposed space missions for mapping CGMs in Lyman UV emission. One is the small UV explorer CAFE (Census of WHIM, Accretion and Feedback Explorer) and the independent external payload LyRIC (Lyman UV Radiation from ISM and CGM) operating on the Chinese Space Station. In the end, I will highlight the prospects in CGM fields based on the existing and future facilities in China.

Speaker: Li Ji (Purple Mountain Observatory, CAS)

3:05 PM Kilohertz Gravitational Wave Detectors

Gravitational wave (GW) detections have ushered in a new era for astronomy, significantly expanding the horizons of gravitational physics and high-energy astrophysics. Numerous GW events originating from compact binary systems have been successfully detected, among which stands out the renowned binary neutron star event, GW170817. This milestone event represents the inaugural joint detection of both GWs and electromagnetic waves, sparking a paradigm shift in our comprehension of neutron star physics and the genesis of heavy elements. However, the (post)merger phase of this event remains elusive due to existing limitations in detector sensitivity. Presently, Advanced LIGO and Virgo detectors exhibit their peak sensitivity in the vicinity of a hundred Hz, while the merger signals manifest at several kilohertz. In this presentation, we shall offer a review of recent findings in kilohertz GW detectors and deliberate on the future prospects in this field.

Speaker: 海兴 缪

5_presentation_final.pdf

1:40 PM → 3:20 PM Neutron Stars: Thursday

Convener: Yuri Levin (Columbia University)

1:40 PM Pulsar Discoveries by FAST

We started the Galactic Plane Pulsar Snapshot (GPPS) survey since 2020, and now have discovered more than 630 pulsars, including pulsars in more than 60 binaries. We found 4 NS-NS binary systems, and many NS-WD systems including the one with the shortest orbit period (53min) probably evolved from Low-Mass X-ray Binaries. We also find many interesting pulsars such as RRATs, and also detected the full-phase emission from many pulsars. The survey results improve many aspects of pulsar astronomy knowledge.

Speaker: JinLin Han (National Astronomical Observatories of Chinese Academy of Sciences)

1_han jinlin_FAST.pptx

2:05 PM Pulsar magnetospheres and their radiation

In this talk I will review recent progress in understanding the complex multi-scale plasma physics of neutron star magnetospheres through the lens of first-principles particle-in-cell simulations. I will highlight pair production discharges near the stellar surface and radiative magnetic reconnection near and beyond the light cylinder. I will extensively discuss their role in powering the multi-wavelength non-thermal radiation of pulsars, which spans almost 20 decades in photon energy, from enigmatic coherent radio waves to recently detected 20TeV emission in Vela.

Speaker: Prof. Alexander Philippov (University of Maryland)

2_Pulsar_Philippov.pdf

2:30 PM Fast radio bursts from magnetars

Active neutron stars generate kHz magnetospheric waves of two types: Alfvén and magnetosonic. As the waves propagate away from the star, they become strongly nonlinear and dissipative. Alfvén waves trigger magnetic reconnection and ejection of relativistic plasmoids. Magnetosonic waves form monster radiative shocks inside the magnetosphere and then launch ultrarelativistic blast waves propagating far outside the light cylinder. These sudden powerful outflows are accompanied by X-ray bursts and fast radio bursts.

Speaker: Andrei Beloborodov

3.pdf

2:55 PM Alfven wave dynamics in the magnetar magnetosphere

Magnetic energy injected into the magnetar magnetosphere is carried by Alfven waves. The dynamics and interactions of Alfven waves are essential in understanding how magnetic energy can be converted into radiations and building theoretical models for magnetar bursts and fast radio bursts. In this talk, I will discuss the dynamics and interactions of Alfven waves, including conversion to fast waves, nonlinear interactions and turbulent dissipation, charge starvation and wave steepening. Especially, nonlinear interactions of Alfven waves can break the MHD condition and lead to efficient particle acceleration. I will also explore the connections to models of fast radio bursts.

Speaker: Xinyu Li (Tsinghua University)

4_alfven_li xinyu.pdf

3:07 PM Understanding various optical transient phenomena with the magentar engine model

A rapidly rotating and highly magnetized neutron star (i.e., magnetar) may be formed in extreme stellar explosions or binary compact star mergers. In observation, the implement of various high-cadence transient surveys has discovered a considerable number of unusual optical transients in the past decades, which are generally analogy to ordinary supernovae but usually distinct in their luminosity or variability timescales. Two representative phenomena are superluminous supernovae (SLSNe) and fast blue optical transients (FBOTs), which could provide a realistic path for studying the magnetar-driven explosions and the corresponding radiation processes. Specifically, the existence of the mangetar engine can lead to the enhancement of the thermal radiation of the supernova ejecta, the shock breakout driven by the magnetar wind, and the leakage of non-thermal radiation from the magnetar wind nebula. Furthermore, the statistical properties of SLSNe and FBOTs and as well as the gamma-ray burst phenomena even indicate a possible united origin for them, which are very likely to be related to a stellar explosion occurring in an interacting close binary system.

Speaker: Prof. Yun-Wei Yu (Central China Normal University)

5_yuyunwei.pdf

3:20 PM → 3:50 PM Coffee Break

3:50 PM → 5:30 PM Accretion Processes: Thursday

Convener: Prof. Yosuke Mizuno (TDLI / Shanghai Jiao Tong University)

3:50 PM Numerical simulations of super-Eddington accretion flows

Super-Eddington flows around black holes, the most powerful energy-production mechanism in the Universe, is thought to exit in very luminous compact objects as ULXs, NLS1s, GRBs, and so on. Super-Eddington accretion may also be responsible for the rapid growth of supermassive black holes in the early universe. By radiation hydrodynamics/magnetohydrodynamics (RHD/RMHD) simulations, it has been shown that in supercritical accretion flows, a large number of photons are swallowed by the black holes with accreting matter due to photon trapping. The strong radiation pressure force supports the thick disks and drives the powerful outflows. The recent general relativistic RMHD simulations of the super-Eddington flows around Kerr black holes also show the BZ effect effectively works and the precession motion occurs.

Speaker: Ken Ohsuga

1-Ken_Ohsuga_texas.pdf

4:15 PM Simulating Super-Eddington Accretion and Outflow Around Stellar-Mass Black Holes

Super-Eddington accretion happens in various astrophysical systems. For example, it is currently believed that super-Eddington accretion onto neutron stars and stellar-mass black holes power a large fraction of ultra-luminous X-ray sources (ULXs). In this work, we conduct a series of 3D general relativistic radiation magnetohydrodynamics (GRRMHD) simulations of highly magnetized accretion flows around stellar-mass black holes. While similar simulations have been performed previously, a systematic investigation of how various physical parameters affect the properties of the disk and outflow has been lacking. Our results disclose that the gas accretion rate crucially determines the outflow-inflow ratio for such accretion flows, while both the gas accretion rate and the black hole spin control the energy output. Our results shed light on understanding super-Eddington systems such as ULXs. We address several questions, such as how luminous the X-ray sources can be, how beamed their emissions are, what determines the power of their winds and jets, etc.

Speaker: Tom Man Kwan (The University of Hong Kong)

2-TomManKwan_Super-Eddington.pdf

4:27 PM Accretion onto black holes with saturated magnetic pressure: from numerical simulations to an analytical model

Using radiation magnetohydrodynamical simulations of accretion onto stellar mass black holes, we revealed that the magnetic pressure, which can be approximated as due to saturated magnetic fields, is the dominant pressure component that supports the vertical structure of the disk. Also, strong disk winds present especially when the mass accretion rate approaches the critical rate. Based on these, we constructed an analytical model that incorporates both outflows and magnetic pressure. We find that, at high accretion rates, the disk is geometrically and optically thick, resembling the slim disk solution; at low accretion rates, the accretion flow consists of a geometrically thin and optically thick outer disk (similar to the standard disk) and a geometrically thick and optically thin inner disk (similar to the ADAF solution). Thus, with the magnetic pressure and outflow, the standard disk truncates and transitions into a hot accretion flow at small radii.

Speaker: Jiahui Huang (Tsinghua University)

3-JiahuiHuang_texas_symposium.pdf

4:39 PM Accreting Supermassive Black Hole Binaries in the Gravitational Wave driven regime

I will summarize theoretical work on accreting supermassive black hole binaries in the gravitational-wave-driven regime. A particular focus is on theoretical predictions of properties of disks and jets in the relativistic regime and its unique signatures where gravitational waves drive the evolution of the system. I will also discuss prospects of dedicated radio VLBI observations and some of their analysis aspects to detect and track similar systems that should simultaneously constitute promising gravitational wave sources. This calls for a comparison of the state of theoretical work to models of single black holes as studied for the Event Horizon Telescope work. The prospect of bringing theoretical and observational efforts as well single and binary accreting black hole studies closer together makes this an exciting field of research for years to come.

Speaker: Roman Gold (University of Southern Denmark)

4-RomanGold_Accreting_Binaries-Texas_in_Shanghai.pdf

5:04 PM X-ray Reflection from Super-Eddington Accretion Flows

X-ray reflection spectroscopy has proven a powerful technique for probing disk geometry and measuring black hole spin in the sub-Eddington accretion regime. Recent observations show that X-ray reflection can also happen in super-Eddington systems such as tidal disruption events. In this work, we conduct a series of general relativistic ray-tracing simulations to model the reflection signatures including the characteristic Fe K lines from super-Eddington accretion flows around black holes. We adopt a lamppost configuration for the corona and a cone geometry for the funnel which is surrounded by winds, with the wind profile inspired by state-of-the-art simulations of super-Eddington accretion. We also allow the photons to be reflected for multiple times in the narrow funnel. Our results show that the Fe K line profile is sensitive to the wind speed, the funnel open angle, and the height of the corona. Therefore, the Fe K lines can be used to effectively probe the funnel and winds produced in super-Eddington accretion. Also, very interestingly, we show that double-peak emission lines can be produced from super-Eddington accretion flow when viewed top-down, which has a physical origin completely different from that produced in thin-disk systems due to Doppler effects.

Speaker: Zijian Zhang (The University of Hong Kong)

5-ZijianZhang_Shanghai.pdf

5:16 PM X-ray Properties of the BHC MAXI J0637-430 during its 2019-20 Outburst

In 2019–20, the transient Galactic black hole candidate MAXI J0637–430 saw its first outburst. Between November 2019 and May 2020, this outburst was active for almost six months. Using archival data from the NICER, Swift, and NuSTAR satellites, we examine the spectral characteristics of this source during that outburst. We examined the source throughout the course of six epochs where Swift/XRT-NuSTAR and NICER-NuSTAR data were simultaneously available. We examined the spectrum data in the large 0.7-70 keV energy band using phenomenological and physical model fitting methods. Disk blackbody with power-law, disk blackbody with broken power-law, and disk blackbody with power-law and bmc models were first combined. We employed the two-component advective flow (TCAF) model with broken power-law, TCAF with power-law, and bmc models to better comprehend the accretion image, such as how the accretion rates change with the changing size of the apparent Compton cloud. The diskbb+power-law and TCAF models were successful in spectrally fitting the data for the last three epochs with acceptable $\chi^2/DOF$. We required an additional component to fit spectra with acceptable $\chi^2/DOF$ for the first three epochs, though. According to our study, during the first three epochs, while the source was in the high soft state, another component may have been present. The bulk motion Comptonization phenomenon is the best way to explain this additional component in this state. We calculated the average mass of the source to be $8.1^{+1.3}_{-2.7}M_{\odot}$ using the TCAF model fitting.

Speaker: Dr Kaushik Chatterjee (South-Western Institute for Astronomy Research, Yunnan University)

6-KaushikChatterjee_Talk.pdf

3:50 PM → 5:30 PM Cosmic Explosions...: Thursday

Convener: Bing Zhang (University of Nevada, Las Vegas)

3:50 PM New Understandings of Gamma-ray Burst Origins & Mechanisms

In this presentation, I will delve into our recent research on Gamma-ray Bursts (GRBs) that deviate from standard classifications or progenitor models. These GRBs encompass a unique event originating from a magnetar giant flare, a distinct short-duration GRB not arising from a compact star merger, and a genuinely long-duration GRB resulting from a compact binary star merger. The discovery of these exceptional phenomena indicates that our current understanding of GRBs is incomplete, warranting further investigation into these extraordinary events to gain a comprehensive understanding of the diverse mechanisms behind GRBs.

Speaker: Binbin Zhang (Nanjing University)

BinbinZhang.pdf

4:15 PM Off-Axis Gamma-Ray Bursts and Electromagnetic Counterparts

We first discuss an off-axis jet model for the short gamma-ray burst (sGRB) 170817A associated with the gravitational wave event GW170817. We show that the origin of the off-axis emission arises from an off-center region of the jet, neither the jet core around the primary axis nor the line of sight at the viewing angle. This off-center location is generally created by the product of the rapidly declining (with angle) jet energy and the increasing beaming term, and can solve spectral puzzles. Then we apply the model to very-high-energy emission from an off-axis GRB. We show that different energy photons (MeV and TeV photons in particular) arrive from different emission zones for off-axis observers even if the emission radius is the same. This off-axis zone-shift effect does not justify the usual one-zone approximation and also produces a time-delay of VHE photons comparable to the GRB duration, which is crucial for future VHE observations, such as by the Cherenkov Telescope Array. If time allows, we will also touch upon cocoon emission from sGRBs and emphasize the difference from that from collapsars.

Speaker: Kunihito Ioka (Yukawa Institute for Theoretical Physics, Kyoto University)

2_ioka.pdf

4:40 PM Quasi-periodic eruptions from stars in mildly eccentric orbits

We propose that quasi-periodic eruptions (QPEs) in galactic nuclei are produced by a low-mass main-sequence star in a mildly eccentric (e ~ 0.5) orbit. We argue that the QPE emission is powered by circularization shocks, but not directly by black hole accretion. The stellar orbits needed to explain QPEs can be efficiently created by the Hills breakup of tight stellar binaries.

Speaker: Wenbin Lu (UC Berkeley)

3_LU_slides.pdf

5:05 PM The velocity distribution of outflows driven by choked jets in stellar envelopes

Many stripped envelope supernovae (SNe) present a signature of high-velocity material responsible for broad absorption lines in the observed spectrum. These include SNe that are associated with long gamma-ray bursts (LGRBs) and low-luminosity GRBs (llGRBs), and SNe that are not associated with GRBs. Recently it was suggested that this high-velocity material originates from a cocoon that is driven by a relativistic jet. In LGRBs, this jet breaks out successfully from the stellar envelope, while in llGRBs and SNe that are not associated with GRBs the jet is choked. Here we use numerical simulations to explore the velocity distribution of an outflow that is driven by a choked jet, and its dependence on the jet and progenitor properties. We find that in all cases where the jet is not choked too deep within the star, the outflow carries a roughly constant amount of energy per logarithmic scale of proper velocity over a wide range of velocities, which depends mostly on the cocoon volume at the time of its breakout. This is a universal property of jets driven outflows, which does not exist in outflows of spherically symmetric explosions or when the jets are choked very deep within the star. We therefore conclude that jets that are choked (not too deep) provide a natural explanation to the fast material seen in the early spectra of stripped envelope SNe that are not associated with LGRBs, and that properties of this material could reveal information on the otherwise hidden jets.

Speaker: Matteo Pais (Hebrew University of Jerusalem)

pais_presentation.pdf

5:15 PM A Unified Progenitor Picture of SLSNe, lGRBs, SNe Ic-BL, and FBOTs

Extreme stripped-envelope supernovae (SESNe), including Type Ic superluminous supernovae (SLSNe-I), broad-line Type Ic SNe (SNe Ic-BL), and fast blue optical transients (FBOTs), are widely believed to harbor a newborn fast-spinning highly-magnetized neutron star (``magnetar''), which can lose its rotational energy via spin-down processes to accelerate and heat the ejecta. The progenitor(s) of these magnetar-driven SESNe, and the origin of considerable angular momentum (AM) in the cores of massive stars to finally produce such fast-spinning magnetars upon core-collapse are still under debate. Popular proposed scenarios in the literature cannot simultaneously explain their event rate density, SN and magnetar parameters, and the observed metallicity. In this talk, we perform a detailed binary evolution simulation that demonstrates that tidal spin-up helium stars with efficient AM transport mechanism in close binaries can form fast-spinning magnetars at the end of stars' life to naturally reproduce the universal energy-mass correlation of these magnetar-driven SESNe. Our models are consistent with the event rate densities, host environments, ejecta masses, and energetics of these different kinds of magnetar-driven SESNe, supporting that the isolated common-envelope formation channel could be a major common origin of magnetar-driven SESNe. The remnant compact binary systems of magnetar-driven SESNe are progenitors of some gravitational-wave transients and galactic systems.

Speaker: Jinping Zhu (Monash University)

5_ZHU jinping.pdf

3:50 PM → 5:30 PM Dark Matter: Thursday

Convener: Jianglai Liu (Shanghai Jiao Tong University)

3:50 PM Searching for Dark Photon Dark Matter with Laser Interferometers and Quantum Sensors

Traditionally, Dark Matter (DM) searches are dominantly focused on GeV – TeV mass window. However, though these experiments have reached unprecedented detection sensitivities, the successes only resulted in a push for stronger limits on parameters. This forces people to keep their minds open to other DM candidates, especially in the different mass regimes. If a DM particle is an ultralight gauge boson, i.e., dark photon, DM should be considered as a background field. With certain assumptions on its coupling to Standard Model particles, this DM background field could either exert forces on test masses in gravitational wave detectors, resulting in displacements with a characteristic frequency set by the gauge boson mass, or source electromagnetic fields within a metal shield which can be probed by state-of-the-art quantum sensors, such as SERF. In this talk, I will discuss a novel strategy to hunt for such DM. I will also give more details about DM background simulation, the properties of the DPDM signal, and the cross-correlation analysis method using LIGO data. The analysis method can be migrated to the one using SERF magnetometer arrays.

We performed the first proof-of-concept U(1)B or U(1)(B-L) DPDM search using LIGO O1 data and improved the constraint using the latest LIGO O3 data. Also, we performed the robust kinetically mixed DPDM lab search at a low-frequency regime using data taken from SERF magnetometer arrays. Large unexplored parameter space can be probed based on this method.

Speaker: Fengwei Yang (University of Florida)

DPDM.pdf

4:10 PM The smallest dark structures

Dark matter halos host galaxies, but cold dark matter is expected to cluster on much smaller scales as well. Small-scale dark matter structures would host no visible matter but can still leave hints about the nature of dark matter. If the dark matter is a thermal relic, the smallest structures are rho ~ r^-1.5 density cusps that arose at the onset of structure formation in the universe. For WIMP models, these cusps may be Earth-mass, and their great abundance and high internal density lead them to dominate the annihilation rate at the present time. Gravitational signatures of small-scale dark structures are more difficult to access, but gravitational detection is possible for minihalos arising in scenarios with amplified small-scale density perturbations.

Speaker: M. Sten Delos (Carnegie Observatories)

2delos.pdf

4:30 PM Dynamics of confinement, slingshot, and primordial black holes as dark matter

Confinement is realised in QCD as well as in several beyond the standard model scenarios. Therefore, it is natural to expect that confining phase transitions took place in the early Universe. In this talk I will show that the unique dynamics of confinement can lead to several phenomenological by-products such as dark matter in the form of primordial black holes and a peculiar gravitational wave spectrum.

Speaker: Michael Zantedeschi (TDLI)

Slingshot TexasInShanghai_final.pdf

4:45 PM Multi-messenger probes on dark matter surrounding a black hole

The environment around the black hole can provide us a promising playground to study the dark matter properties because of the large dark matter density from accretion.
I will explore the multi-messenger probes on the dark matter in the vicinity of black holes. More concretely, I will discuss (1) the gravitational wave signals from a black hole binary whose dynamics is affected by the dark matter (2) the multi-wavelength signals covering the radio, optical and gamma rays arising from the dark matter annihilation.

Speaker: kenji kadota

4kadota1.pdf

5:00 PM Probing Ultralight Dark Matter with Gravitational-Wave Detectors in Space

Ultralight bosonic fields (ULBFs) are predicted by various theories beyond the standard model of particle physics and are viable candidates of cold dark matter. There have been increasing interests to search for the ULBFs in physical and astronomical experiments. In this paper, we investigate the sensitivity of several planned space-based gravitational-wave interferometers to ultralight scalar and vector fields. Using time-delay interferometry (TDI) to suppress the overwhelming laser frequency noise, we derive the averaged transfer functions of different TDI combinations to scalar and vector fields, and estimate the impacts of bosonic field's velocities. We obtain the sensitivity curves for LISA, Taiji and TianQin, and explore their projected constraints on the couplings between ULBFs and standard model particles, illustrating with the ULBFs as dark matter.

Speaker: Yong Tang (University of Chinese Academy of Sciences)

5 Texas_Yong_Tang.pdf

5:15 PM Ultra-high frequency gravitational waves from inflaton decay

Since the models of inflation compatible with CMB data require non-renormalizable inflaton potentials, it is natural to have extra couplings between inflaton and gravitons. The suppression scale of such operators can well be lower than the Planck scale. Due to these couplings, inflaton can produce high frequency gravitons during reheating due to both decay and bremsstrahlung process. In my talk, I will present results of computation of the gravitational wave signal strength coming from these processes, as well as graviton contribution to the number of relativistic degrees of freedom. Remarkably, in the case of low reheating temperature, even Planck-suppressed operators lead to potentially measurable contribution to the dark radiation.

Speaker: Anna Tokareva (Hangzhou Institute for Advanced Study)

Tokareva presentation.pdf

3:50 PM → 5:30 PM Gravitational Lensing: Thursday

Convener: Jun Zhang (Shanghai Jiao Tong University)

3:50 PM Extrasolar planets with gravitaitonal microlensing

I will first review the current status of extrasolar planet discoveries with graviational microlensing, and then discuss the future aspects with space missions such as the Earth 2.0 satellite.

Speaker: Prof. Shude Mao (Tsinghua University)

1_smao_good.pdf

4:15 PM Highly Magnified Extragalactic Stars

Thanks to extreme gravitational lensing magnification factors realized near the lensing caustics cast by galaxy cluster lenses, the most massive and short-lived stars in the Universe can be individually observed at cosmological distances. In this talk, I will demystify the phenomenology of these highly magnified stars, in particular the effect of intracluster microlensing. Additionally, I will explain how observing those can advance our knowledge of massive stars, and how this phenomenon can be exploited as an exquisite probe of dark matter mini-structures on sub-galactic scales. I will summarize recent observational progress in this area of study, and provide a future outlook.

Speaker: Prof. Liang Dai (University of California, Berkeley)

2_texas_highly_magnified_stars.pdf

4:40 PM Strongly Lensed Transient Sources

The past decades have witnessed a lot of progress in gravitational lensing with two main targets: stars and galaxies (with active galactic nuclei). The success is partially attributed to the continuous luminescence of these sources making the detection and monitoring relatively easy. With the running of ongoing and upcoming large facilities/surveys in various electromagnetic and gravitational-wave bands, the era of time-domain surveys would guarantee constant detection of strongly lensed explosive transient events, for example, supernovae in all types, gamma ray bursts with afterglows in all bands, fast radio bursts, and even gravitational waves. Lensed transients
have many advantages over the traditional targets in studying the Universe, and magnification effect helps to understand the transients themselves at high redshifts. In this talk, on base of the recent achievements in literature, I summarize the methods of searching for different kinds of lensed transient signals, the latest
results on detection and their applications in fundamental physics, astrophysics, and cosmology. At the same time, I give supplementary comments as well as prospects of this emerging research direction that may help readers who are interested in entering this field.

Speaker: Kai Liao (Wu)

3_Lensed_Transients_Liao_Shangshai.pptx

5:05 PM PEXO: A Global Modeling Framework for Nanosecond Timing, Microarcsecond Astrometry, and μm/s Radial Velocities

Motivated by detecting Earth twins in extreme precise radial velocity data, PEXO is a package aiming for extremely high-precision modeling of the motion of single stars or stars in a system. PEXO is general enough to account for binary motion and stellar reflex motions induced by dark companions and is precise enough to treat various relativistic effects both in the solar system and in the target system. We also model the post-Newtonian barycentric motion for future tests of general relativity in binaries. We benchmark PEXO with the pulsar timing package TEMPO2 and find that PEXO produces numerically similar results with timing precision of about 1 nanosecond, space-based astrometry to a precision of 1 μas, and radial velocity of 1 μm/s and improves on TEMPO2 for decade-long timing data of nearby targets, due to its consideration of third-order terms of Roemer delay. PEXO is able to avoid the bias introduced by decoupling the target system and the solar system and to account for the atmospheric effects that set a practical limit for ground-based radial velocities close to 1 cm/s. Considering the various caveats in barycentric correction and ancillary data required to realize cm/s modeling, we recommend the preservation of original observational data.

Speaker: Fabo Feng (TDLI)

4_texas_symposium2023.pptx

Friday, December 15

8:40 AM → 10:20 AM Astroparticle: Friday

Convener: Hao Zhou (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

8:40 AM LHAASO observations of the BOAT GRB 221009A

In this talk, I will report the observations of the TeV emission from the brightest-of-all-time GRB 221009A by the Large High Altitude Air Shower Observatory (LHAASO). I will also present our understanding of the TeV and multi-wavelength afterglow emission of this unusual GRB.

Speaker: Xiang-Yu Wang

1_TEXAS-wang.pptx

9:05 AM Extreme particle acceleration at AGN jet termination shocks

Extragalactic plasma jets are some of the few astrophysical environments able to confine ultra-high-energy cosmic rays, but whether they are capable of accelerating these particles is unknown. In this work, we revisit particle acceleration at relativistic magnetized shocks beyond the local uniform field approximation, by considering the global transverse structure of the jet. Using large two-dimensional particle-in-cell simulations of a relativistic electron-ion plasma jet, we show that the termination shock forming at the interface with the ambient medium accelerates particles up to the confinement limit. The radial structure of the jet magnetic field leads to a relativistic velocity shear that excites a von Kármán vortex street in the downstream medium trailing behind an over-pressured bubble filled with cosmic rays. Particles are efficiently accelerated at each crossing of the shear flow boundary layers. These findings support the idea that extragalactic plasma jets may be capable of producing ultra-high-energy cosmic rays. This extreme particle acceleration mechanism may also apply to microquasar jets.

Speaker: Gwenael Giacinti (TDLI & SJTU)

2_Giacinti_Texas_2023.pdf

9:17 AM A parameter study of the hadronic synchrotron mirror model on 3C279

Speaker: Laenita De Jonge

3_Texas_2023_LDJ.pdf

9:29 AM H.E.S.S. observations of composite Seyfert–starburst galaxies

Context. Composite galaxies, containing both a starburst and Seyfert component, may produce very-high-energy (VHE; > 100 GeV) γ-ray emission at vastly different spatial scales ranging from several Schwarzschild radii of a supermassive black hole (SMBH) to a dozen kiloparsecs. Some cosmic-ray sources, including cores of active galaxies, heads of kiloparsec-scale jets, and galactic superwinds, additional to core-collapse supernova remnants were suggested to explain multi-wavelength and/or muti-messenger data collected on composite galaxies. For a variety of scenarios VHE γ-ray observations are expected to provide stringent constraints on cosmic-ray populations in these systems.
Aims. The closest composite Seyfert–starburst galaxies, NGC 1068, the Circinus galaxy, and NGC 4945, are investigated for being γ-ray emitters with the High Energy Stereoscopic System (H.E.S.S.). Most of the H.E.S.S. NGC 1068 observations were taken prior to the observations by the Major Atmospheric Gamma Imaging Cherenkov telescopes in order to provide coverage of NGC 1068 observations in time and tighten the previously reported H.E.S.S. flux upper limit by factor of 10. The H.E.S.S. observations of the Circinus galaxy and NGC 4945 were taken with the purpose to provide the first constraints on their VHE γ-ray signals.
Methods. Data obtained in dedicated H.E.S.S. observations have been analyzed to search for VHE γ-ray counterparts to the detected Fermi-LAT GeV γ-ray signals and for potential spectral sub-components substantially emitting in the VHE range.
Results. No signals have been found in these H.E.S.S. data. Upper limits on the VHE γ-ray fluxes are derived and are compared to models, involving starburst activities in NGC 1068 and NGC 4945, kiloparsec-scale bubbles in NGC 1068 and the Circinus galaxy, possible multiple components in NGC 4945 previously suggested from Fermi-LAT data, propagation of VHE γ rays for a SMBH surrounded by gas or photons in NGC 1068, and at last hypothetical sources of ultra-high-energy cosmic rays in NGC 4945.
Conclusions. The H.E.S.S. observations of the nearby composite Seyfert-starburst galaxies probe a broad range of energetic astrophysical phenomena. The non-detection of NGC 1068, the Circinus galaxy, and NGC 4945 in the H.E.S.S. data has implications on the cosmic-ray populations existing under different physical conditions.

Speaker: Andrew Chen (University of the Witwatersrand)

4_Chen_Texas_Symposium_2023_shortened2.pdf

9:41 AM Constraining the Sources of UHECRs

UHECRs are composed of intermediate-mass nuclei and have a composition evolution with energy that is roughly consistent with a Peters Cycle, such that the mean rigidity is less than 5 EV, even at relatively high energy. Deflections in the Galactic magnetic field are in general large, and identifying sources by angular correlations has been impossible so far. Nonetheless, a number of indirect constraints can help narrow the range of candidate UHECR accelerators, as I will discuss.

Speaker: Glennys Farrar (New York University)

5_Texas121523_Farrar.pdf

10:06 AM Arguments in Favor of Cluster Accretion Shocks as the Source of Ultra-High-Energy Cosmic Rays

The origin of ultra-high-energy cosmic rays remains unknown owing to the lack of definitive observational evidence and the lack of a source class without major theoretical objections. The primary challenge for cluster accretion shocks—formed by accretion of gas beyond the virial radius of galaxy clusters—is the purported lack of sufficient magnetic field strength to scatter cosmic rays at the highest energies. However, we argue that the many advantages of our revised cluster-shock model, including the abundance and power of the shocks, the lowest ambient photon background of any source, the growing cosmic ray luminosity with time, and an explanation for the transition from a light to heavy composition, warrant further investigation for this source class. We speculate on ways the upstream cosmic rays may incite magnetic fields of sufficient strength, and we highlight the observational tests of this model.

Speaker: Dr Paul Simeon (Stanford University)

8:40 AM → 10:20 AM Cosmology with large-scale structure: Friday

Convener: Yu Yu (Shanghai Jiao Tong University)

8:40 AM Neutrino (and other particle) physics with large-scale structure

The standard hot big bang predicts a background of relic neutrinos analogous to the CMB. At an average of ~300 neutrinos per cubic centimetre, these neutrinos are a formidable presence that can influence the evolution of the universe in many different ways. In this talk, I will discuss what one could learn about the neutrino sector from large-scale structure, as well as some recent works on the modelling of massive neutrinos.

Speaker: Yvonne Wong (University of New South Wales)

1-yyyw.pdf

9:00 AM Understanding the cosmic acceleration with massive galaxy surveys

The cosmic acceleration, first probed by observations of SNIa in 1998, is one of the most significant discoveries in modern sciences. In the past 25 years, extensive studies have been performed to unveil the physical origin of this surprising phenomenon, including studies on dark energy and modified gravity. In this talk, I will report the latest progress in this field, and focus on cosmological implications of large galaxy surveys including eBOSS, DESI and PFS.

Speaker: Prof. Gongbo Zhao (NAOC)

2-Texas2023_GBZHAO.pdf

9:20 AM Forward Model the Universe in the Era of Deep Learning

Rapid advances in deep learning have brought not only myriad powerful neural network models, but also breakthroughs that benefit established scientific research. In particular, automatic differentiation (AD) tools and computational accelerators like GPUs have facilitated forward modeling of the Universe with differentiable simulations. I will talk about our recent progress on developing computation and memory efficient simulation based modeling at the field level, with accuracy highly optimized by combining differentiable physical models, trainable neural networks (with physical inductive biases including symmetry and dimensional analysis), and symbolic regression.

Speaker: Yin Li

Copy of pmwd.pdf

9:40 AM Non-linear flows for the neutrino masses

Recently, I developed a non-linear multi-flow perturbation theory for massive neutrinos and other free-streaming particles, called Flows For The Masses. It bins their initial Fermi-Dirac distribution into discrete momenta, with neutrinos of each initial momentum treated as a separate fluid obeying the continuity and Euler equations of motion. I describe its non-linear corrections, based upon a generalization of the Time-Renormalization Group perturbation theory, and their acceleration by over two orders of magnitude using Fast Fourier Transform techniques. Then, I discuss ongoing work to emulate the massive neutrino power spectrum in cosmologies with rapidly-varying dark energy, and I propose further applications to N-body simulations.

Speaker: Amol Upadhye (Yunnan University)

4-upadhye_texasInShanghai_2023-12-15.pdf

9:50 AM Alleviating H0-tension in T-dual Friedmann cosmologies

With increasing significance, the H0-tension between the Local Distance Ladder and Planck ΛCDM-analysis of the CMB points to a new principle of cosmological spacetime. Distinct from conventional extrapolations of general relativity in the Solar system, cosmological spacetime contains heat as a relic of the Big Bang based on Planck scale structures in black hole spacetimes. A path integral formulation produces a system of equations that satisfy T-duality in the Friedmann scale factor - a new symmetry in the Hubble expansion H(z) \simeq (1+(6/5)OmegaM0[(1+z)^5-1])^{1/2}/(1+z). It satisfies H0 \simeq 73 km/s/Mpc, q0 \simeq -1, OmegaM0 \simeq 0.25 relevant to tensions in (H0,q0,S8). [Based on van Putten, 2021, Phys. Lett. B, 823, 13637; 2020, MNRAS 491, L6.]

Speaker: maurice van putten (INAF-OAS, Sejong University)

5-vanPuttenH0.pdf

10:00 AM The Scale Invariant Vacuum Paradigm: Main Results and the Current BBNS Progress

The talk will present a summery of the main results within the Scale Invariant Vacuum (SIV) paradigm as related to the Weyl Integrable Geometry (WIG) as an extension to the standard Einstein General Relativity (EGR). After a short sketch of the mathematical framework, the main results until 2023 [1] will be highlighted in relation to: the inflation within the SIV [2], the growth of the density fluctuations [3], the application of the SIV to scale-invariant dynamics of galaxies, MOND, dark matter, and the dwarf spheroidals [4], as well as MOND as a peculiar case of the SIV theory [5], along with the most recent results on the BBNS light-elements’ abundances within the SIV [6].
Keywords: cosmology: theory, dark matter, dark energy, inflation, BBNS; galaxies: formation, rotation; Weyl integrable geometry; Dirac co-calculus.
[1] Gueorguiev, V. G., and Maeder, A., The Scale Invariant Vacuum Paradigm: Main Results and Current Progress. Universe 2022, 8(4), 213; DOI: 10.3390/universe8040213; arXiv: 2202.08412 [gr-qc].
[2] Maeder, A. and Gueorguiev, V. G., Scale invariance, horizons, and inflation. MNRAS 504, 4005 (2021). arXiv: 2104.09314 [gr-qc].
[3] Maeder, A. and Gueorguiev, V., G., The growth of the density fluctuations in the scale-invariant vacuum theory, Phys. Dark Univ. 25, 100315 (2019). arXiv: 1811.03495 [astro-ph.CO].
[4] Maeder, A. and Gueorguiev, V.G. Scale-invariant dynamics of galaxies, MOND, dark matter, and the dwarf spheroidals, MNRAS 492, 2698 (2019). arXiv: 2001.04978 [gr-qc].
[5] Maeder, A. MOND as a peculiar case of the SIV theory, MNRAS 520, 1447 (2023); arXiv: 2302.06206 [gr-qc]; [6] V. G. Gueorguiev and A. Maeder, Big-Bang Nucleosynthesis within the Scale Invariant Vacuum Paradigm, arXiv: 2307.04269 [nucl-th].

Speaker: Dr Vesselin Gueorguiev (Institute for Advanced Physical Studies, Sofia, Bulgaria and The Ronin Institute for Independent Scholars, NJ, USA)

10:10 AM Galaxy clustering at small scale and measurement of structure growth

The spatial distribution of galaxies contains a significant amount of information of the underlying cosmology. However, fully extracting this information can be challenging, especially at small scale due to the non-linearity of the dark matter dynamics, as well as the complicated physics of galaxy formation and evolution. I will introduce the emulator approach in the modeling of galaxy large scale structure and focus on non-linear scale using high resolution N-body simulations. I will also introduce the latest result from the application to the data of massive galaxies from BOSS and eBOSS survey. The analysis reports a tight constraint on the linear growth rate with some tension with other experiments. I will show follow-up works and extensions from both observational side and modeling side.

Speaker: Zhongxu Zhai

7-ZhongxuZhai_TexasInShanghai.pdf

8:40 AM → 10:20 AM GW Astrophysics: Friday

8:40 AM Probing the Origin of Black Hole Binary Mergers with Gravitational Wave Modulations

A major outstanding challenge is how to observationally infer the formation of black hole mergers using gravitational waves alone. I will discuss and show how several likely formation channels will give rise to modulations of the gravitational wave signal, which can be modeled and looked for with current (LIGO/Virgo) and future (3G) ground-based observatories. Modulations of the gravitational wave signal might be the only way to distinguish the growing list of suggested formation pathways apart with gravitational waves alone. Modeling and looking for such modulations, i.e. deviations from 2-body isolated vacuum inspirals, will start to play a key-role in the coming years when sensitivity increases.

Speaker: Prof. Johan Samsing (NBI)

9:00 AM Future facilities for electromagnetic observations of dual and binary SMBHs

I will review upcoming survey facilities for electromagnetic observations of dual (~kpc) and binary (~sub-pc) SMBHs. I will highlight the combined power of Rubin, Euclid, and Roman in exploring the unexplored parameter space that is particularly important for multi-messenger astronomy.

Speaker: Xin Liu (University of Illinois at Urbana-Champaign)

（2）Liu_TexasSymposium.pdf

9:20 AM Gravitational Lensing of Gravitational Wave Events and Their Applications

Gravitational lensing of gravitational waves is one kind of important phenomena that the current and future gravitational wave experiments are going to discover. The gravitational lensing of gravitational waves is expected to provide a unique probe to not only the nature of gravitational waves but also the nature of dark matter and cosmology. In this talk, we will briefly summarize the theoretical prediction on the detection of lensed gravitational wave events by various gravitational wave detectors and the detectability of lensed host galaxies/electromagnetic counterparts for some of them. We will also discuss the prospects on constraining the dark matter nature and the Hubble constant via the diffractive lensing and strong lensing of compact binary merger events.

Speaker: Prof. Youjun Lu (CAS)

9:40 AM Shape eccentricity and the moment of inertia for rotating neutron stars

I will talk about a tight universal relation between the shape eccentricity and the moment of inertia for rotating neutron stars that we discovered recently.

Speaker: Lijing Shao (Peking University)

（4）20231215_shao_shanghai.pdf

10:00 AM GW Results from the European Pulsar Timing Array

Pulsar Timing Arrays (PTAs) search for nHz gravitational waves by timing the radio signals from a network of stable millisecond pulsars and looking for a spatially correlated common signal in the data set. We expect to find a gravitational wave background (GWB) first, followed by possible individual sources. PTAs have reported the finding of evidence for such a GWB signal in various data sets, namely NANOGrav, Australian PPTA, EPTA+InPTA and CPTA. They coordinate their work together in the IPTA.

The European Pulsar Timing Array has released the second data set DR2 with 25 millisecond pulsars. I will focus on the recent results that the EPTA+InPTA collaborations have published simultaneously in the a coordinated process with NANOGrav, PPTA and CPTA. The EPTA reports a nominal amplitude of 2.5e-15 for a common red signal, which is consistent with the other PTA results. We find a significance of >3 sigmas for the characteristic spatial correlations required for a GWB. This follows a general positive trend across different PTAs with evidences between 2 and 4.6 sigmas in favour of the gravitational wave origin of the common signal. This putative signal can be tested against both cosmological and astrophysical sources for a GWB and be used to put constraints for various theories. The EPTA has also searched for a single resolvable GW source in the DR2. Although, some hints were found, no conclusive detection has been made.

Speaker: Siyuan Chen (KIAA, PKU)

（5）Texas_epta_chen.pdf

10:10 AM Testing fundamental physics with PTA and astrometry measurements of stochastic gravitational wave background

The detection of gravitational waves from the LIGO/Virgo collaboration provides an excellent probe for the fundamental physics of gravity, and the recent pulsar timing arrays (PTA) detections of stochastic gravitational wave background (SGWB) open a new window due to their different frequency sensitivity (nHz band). We explore the possibility of testing gravity using PTA signals by studying the impact of modified gravity on the angular correlation of the overlap reduction function (in GR it is approximated by the Hellings-Downs curve). We find a distinct signature, a shift in the minimal angle of the angular distribution, and demonstrate that this shift is quantitatively sensitive to any change in the phase velocity.
On the other hand, astrometry also holds the potential to detect SGWB by precisely measuring the stellar positions. We explore the feasibility of using astrometry for the identification of parity-violating signals which is not possible in PTA measurements. This is achieved by defining and quantifying a non-vanishing EB correlation function within astrometric correlation functions, and investigating how one might estimate the detectability of such signals.
(The talk is mainly based on https://arxiv.org/abs/2308.16183 and https://arxiv.org/abs/2309.16666)

Speaker: Meng-Xiang Lin (University of Pennsylvania)

（6）Lin_MX_Texas_2023.12.15.pptx

8:40 AM → 10:20 AM Neutron Stars: Friday

Convener: Shuai Zha (Yunnan Observatories, Chinese Academy of Sciences)

8:40 AM Superfluid dynamics in neutron star crusts

I will discuss 3-dimensional simulations of pinning and unpinning of individual vortices and speculate on what happens to them during a glitch. I will also discuss a very simple evolutionary models for pinned vorticity in spinning-down neutron stars, and show that vortex loops and "rivers" inside them arise quite naturally in such models.

Speaker: Yuri Levin (Columbia University)

1.pdf

9:05 AM Quark degrees of freedom in neutron stars

Recent neutron star observations coupled with the theoretical understanding emerging of the role that quark degrees of freedom play in supporting neutron stars are providing a consistent picture of neutron star interiors. An important key is the finding by the NICER telescope that massive neutron stars have considerably larger radius than nuclear degrees of freedom alone can explain. I will illustrate this picture with a discussion of modern quark-hadron crossover equations of state.

Speaker: Gordon Baym (University of Illinois)

Baym-nstars shanghai.pdf

9:25 AM Neutron Stars as Laboratories for Nuclear and Particle Physics.

I will discuss efforts to interpret recent multi-messenger observations of neutron stars using advances in theory and modeling. These studies have provided new insights into the sound speed in dense matter and low-temperature properties, such as its specific heat and transport phenomena. Neutron stars can also be excellent sites to look for dark matter. I will briefly discuss harnessing neutron star observations to constrain or discover dark matter candidates with sub-GeV masses. I will comment on how next-generation gravitational wave observatories such as Cosmic Explorer and Einstein Telescope can revolutionize the field and outline their discovery potential.

Speaker: Sanjay Reddy (University of Washington)

3.pptx

9:50 AM Spindown of Pulsars Interacting with Companion Winds

The spindown of isolated pulsars, both aligned and oblique, has been extensively studied over the past few decades. However, in some binary systems, the interaction of pulsar magnetosphere and the wind from the companion can alter the rate of pulsar spindown. In this study, we use the particle-in-cell method to measure the spindown of pulsars surrounded by relativistic winds from companion stars, where the stand-off distance between the magnetosphere and the shocked wind is well inside the light cylinder of the pulsar. Our results show that the spindown of the aligned component is enhanced due to the confinement of the magnetosphere by the wind, while the oblique component is suppressed due to the mismatch between the pulsar wind stripe wavelength and the waveguide formed by the cavity in the companion wind. This difference from the well-known spindown formula affects the estimate of the surface magnetic field strength in observed pulsar systems. We apply our findings to the double pulsar system PSR J0737–3039, where a normal 2-second pulsar PSR J0737–3039B is thought to be surrounded by a wind produced by its millisecond companion PSR J0737–3039A, with a shock stand-off distance estimated to be 1/3 of its light cylinder. We provide updated estimates of magnetic field strength of PSR J0737–3039B, and discuss the implications for its high energy emission and radio eclipse mapping.

Speaker: Yici Zhong (The University of Tokyo)

YiciZhong.pdf

10:02 AM Probing hadron-quark phase transition in inspiralling neutron stars

The discovery of GW170817 has significantly advanced our understanding of the high-density equation of state. In this poster, I will showcase our recent studies that involve constraining the hadron-quark phase transition using both the existing GW170817 data and future GW observations. The discussion will encompass the constraints derived not only from quasi-equilibrium tides, but also from dynamic tides.

Speaker: Zhiqiang Miao (TDLI)

5.pptx

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 12:30 PM Accretion Processes: Friday

Convener: Roman Gold (University of Southern Denmark)

10:50 AM Variability of Active Galactic Nuclei

The restless central engine of accreting supermassive black holes (AGNs) produces ubiquitous variability across broad ranges of wavelengths and timescales. Variability allows the study of the innermost structures around the SMBH that cannot be spatially resolved directly. Recent studies on AGN variability have revealed interesting patterns in the light curves of AGNs, providing critical insights on the physics of accretion processes. I will review these recent progresses and applications of AGN variability to the general field of SMBHs.

Speaker: Yue Shen

11:15 AM Wind from black hole accretion disk in AGNs

Winds from black hole accretion system are very common phenomena. Two promising mechanisms driving winds are magnetic driven and radiation line force driven. I will introduce the numerical simulations of magnetic driven wind from black hole accretion disk. I will also introduce the numerical simulations of winds driven by the combination of radiation line force and magnetic force. These results can be used to understand the wind phenomena from AGNs.

Speaker: Defu Bu (Shanghai Astronomical Observatory)

2-DefuBu_Accretion_Processes.pdf

11:27 AM Investigation into the excess infrared emission detected from the west hot spot of the radio galaxy Pictor A: a possible evidence of the turbulence acceleration.

From the west hot spot of the radio galaxy Pictor A, excess infrared emission above the radio-to-optical synchrotron emission was detected in the range of 1-100 THz range with the Herschel and WISE observatories. In order to find out the nature of the infrared excess, submillimeter photometry was performed with the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array at the frequency of 405 GHz. A submillimeter source was detected at the position of the west hot spot, while no significant emission was revealed from diffuse structures associated to the hot spot.This indicates that the excess infrared emission originates in the west hot spot itself rather then contamination from the diffuse structure. Because the derived submillimeter flux of the west hot spot, a 405 GHz flux density of 80.7 +- 3.1 mJy, agrees with the extrapolation from the synchrotron radio spectrum, the excess infrared emission is suggested to exhibit no major contribution at 405 GHz.

By ascribing the excess infrared emission to the substructures resolved with the Very Long Baseline Array within the hot spot, the spectrum of the excess was simply modeled with a broken power-law model subjected to a high-frequency cut off, which is widely adopted for studies of particle acceleration under a continuous energy injection condition. The low-frequency spectral index of the excess emission (alpha = 0.06 +- 0.35) is found to be exceptionally harder than the prediction from the diffusive shock acceleration (alpha > 0.5). As a result, an attractive scenario is proposed that the excess infrared emission is generated through the post-shock turbulence acceleration (so-called the Fermi-II acceleration) operated in the substructures.

Speaker: Naoki Isobe (ISAS/JAXA)

3-NaokiIsobe_PicA_WestHS_Texas32_20231215.pdf

11:39 AM A surprising excess of radio emission in extremely stable quasars: a unique clue to jet launching?

Quasars are generally divided into jetted radio-loud (RL) and non-jetted radio-quiet (RQ) ones, but why only roughly 10% quasars are radio loud has been puzzling for many decades. Other than jet-induced-phenomena, black hole mass, or Eddington ratio, prominent difference between jetted and non-jetted quasars has scarcely been detected. Here we show that a unique distinction between them and the mystery of jet launching could be disclosed by a surprising excess of radio emission in extremely stable quasars (ESQs, i.e., type 1 quasars with extremely weak variability in UV/optical over 10 years). Specifically, we find that > 25% of the ESQs are detected by FIRST/VLASS radio survey, while only $\sim$ 6-8% of its control sample, matched in redshift, luminosity, and Eddington ratio, are radio detected. The excess of radio detection of ESQs has a significance of 4.4 $\sigma$ (99.9995%), and dominantly occurs at intermediate radio loudness with $\sim$ 10 - 60. The radio detection fraction of ESQs also tends to increase in the ESQ samples selected with more stringent thresholds. Our results reverse the common view that RL quasars are likely more variable in UV/optical due to jet contamination. New clue/challenge posed by our findings imminently demands extensive follow-up observations to probe the nature of jets in ESQs, and theoretical studies on the link between jet launching and ESQs. Moreover, the discovery makes ESQs, a population which has never been explored, unique targets in the blooming era of time domain astronomy, like their opposite counterparts of quasars exhibiting extreme variability or changing-look feature.

Speaker: Zhen-Yi Cai (University of Science and Technology of China)

11:51 AM Standing shocks in accretion flows around black holes and associated observational signatures

Low angular momentum flows around black holes are likely to form standing shocks during the accretion processes. The shocks possibly encounter instabilities leading to various observational signatures associated with inflows and outflows. In our work, we address a range of issues like flaring in under-luminous Sgr A* with supermassive black hole and outflow properties in super-accretors like SS 433 and ultraluminous X-ray sources with stellar-mass black holes.

References:

1. T. Okuda , C.B. Singh, R. Aktar, 2023, MNRAS, 522, 1814.

2. T. Okuda , C.B. Singh C.B., R. Aktar, 2022, MNRAS, 514, 5074.

3. C.B. Singh, T. Okuda, R. Aktar, 2021, RAA, 21, 134.

4. T. Okuda, C.B. Singh, 2021, MNRAS, 503, 586.

Speaker: Chandra Bahadur Singh (Yunnan University)

5-ChandraSingh_texas_Dec2023.pdf

12:03 PM Helical and nonhelical large-scale dynamos in thin accretion discs

The dynamics of accreting and outgoing flows around compact objects depends crucially on the strengths and configurations of the magnetic fields therein, especially of the large-scale fields that remain coherent beyond turbulence scales. Possible origins of these large-scale magnetic fields include flux advection and disc dynamo actions. However, most numerical simulations have to adopt an initially strong large-scale field rather than allow them to be self-consistently advected or amplified, due to limited computational resources. The situation can be partially cured by using sub-grid models where dynamo actions only reachable at high resolutions are mimicked by artificial terms in low-resolution simulations. In this work, we couple thin-disc models with local shearing-box simulation results to facilitate more realistic sub-grid dynamo implementations. For helical dynamos, detailed spatial profiles of dynamo drivers inferred from local simulations are used, and the nonlinear quenching and saturation is constrained by magnetic helicity evolution. In the inner disc region, saturated fields have dipole configurations and can reach $\beta\simeq 0.1$ to $100$, with correlation lengths $\simeq h$ in the vertical direction and $\simeq 10h$ in the radial direction, where $h$ is the disc scale height. The dynamo cycle period is $\simeq 40$ orbital time scale, compatible with previous global simulations. Additionally, we explore two dynamo mechanisms which do not require a net kinetic helicity and have only been studied in shearing-box setups. We show that such dynamos are possible in thin accretion discs, but produce field configurations that are incompatible with previous results. We discuss implications for future general-relativistic magnetohydrodynamics simulations.

Speaker: Hongzhe Zhou (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

6-hongzhe_zhou_texas.pdf

12:15 PM High-soft to low-hard state transition in black hole X-ray binaries

To understand the decaying phase of outbursts in BH-XRBs, we performed very long GRMHD simulations of a geometrically thin accretion disk around a Kerr BH with slowly rotating matter injected from outside. Due to the interaction between the thin disk and injected matter, the accretion flow near the BH goes through different phases. The sequence of phases is: soft state $\rightarrow$ soft-intermediate state $\rightarrow$ hard-intermediate state $\rightarrow$ hard state $\rightarrow$ quiescent state. The talk will discuss the process of transition in detail. We also observed low-frequency QPOs ($\sim 10$Hz) and high-frequency QPOs ($\sim 200$Hz) throughout the evolution.

Speaker: Indu Kalpa Dihingia (TDLI-SJTU)

7-Indu_TexasSymposium.pdf

10:50 AM → 12:30 PM Gravitational Lensing: Friday

Convener: Pengjie Zhang (Shanghai Jiao-Tong University)

10:50 AM SuperBIT balloon-borne telescope

SuperBIT telescope was carried to the top of the Earth's atmosphere in April/May 2023, by a helium balloon the size of a sports stadium. For 40 days and 45 nights it circumnavigated the Southern hemisphere 5.5 times. Using image stabilisation, it achieved diffraction-limited UV and optical imaging. We mapped the weak gravitational lensing signal of merging galaxy clusters like the Bullet Cluster, to track the dynamics of dark matter during astronomically large collider experiments. Cosmological simulations suggest that these mergers will be the best place to measure any cross-section for interaction between dark matter particles (and not with ordinary matter), caused by forces predicted by extensions to the particle physics standard model but restricted to the dark sector.

Speaker: Richard Massey (Durham University, UK)

1_Richard_Massey_Shanghai_SuperBIT_upload.pdf

11:15 AM Weak lensing cosmology beyond two-point shear correlations

With the fast development of high-precision large photometric surveys, weak lensing (WL) effects have become one of the major probes in cosmology. While the two-point shear correlations are the most extensively employed analyses, other statistics beyond that are desired because of the non-Gaussian nature of cosmic structures. In this presentation, I will discuss the cosmological application of WL peak statistics, particularly the high peak statistics, which are closely related to nonlinear massive halos. Besides the commonly adopted peak height statistics, a new analysis based on the peak steepness will also be presented, and the relevant systematics will be discussed. In addition, I will also discuss the potential of combining WL shear and magnification effects to calibrate the shear multiplicative bias using data alone.

Speaker: Prof. Zuhui Fan (Yunnan University)

Texas2023_SJTU_ZFan.pdf

11:40 AM Seeking Lensing Effects from Counting Galaxies

Weak gravitational lensing induces flux dependent fluctuations in the observed galaxy number density distribution. This cosmic magnification (magnification bias) effect in principle enables lensing reconstruction alternative and independent to cosmic shear and CMB lensing. However, the intrinsic galaxy clustering overwhelms the lensing signal, and hindered its application. We developed various novel methods to extract the lensing magnification signal with different assumptions and under various circumstances. The statistical significance and the potential systematics are quantified using simulations heading at Stage IV survey conditions. The predicted S/N for magnification-shear cross correlation can achieve 200 for LSST-like survey. Finally, we present a weak lensing convergence map reconstructed from the clustering of DECaLS galaxies of the DESI imaging surveys. The detection of the magnification-shear cross correlation over 1/5 sky area reaches 𝑆/𝑁=10.

Speaker: Yu Yu (Shanghai Jiao Tong University)

Texas-YUYU.pdf

11:55 AM Towards precision cosmology ---- systematics removal with Stage III data

Precision cosmology is a very important target for the coming Stage IV weak lensing studies. It is also hard to achieve due to multiple systematical errors. In this talk, we present systematics mitigation performed in 2 published papers and some ongoing works. More specifically, we present intrinsic alignment mitigation with KiDS data, and shear bias removal as well as redshift error measurements with DECaLS data and Obiwan image simulation. With the experience of the calibrations with current Stage III data, we forecast the requirements for CSST systematics control, which will guide our calibration process in the future.

Speaker: Ji Yao (Shanghai Astronomical Observatory)

4_Yao lensing sys.pdf

12:10 PM Quasi-2D Weak Lensing Cosmological Constraints Using the PDF-SYM method

Cosmic shear statistics, such as the two-point correlation function (2PCF), can be evaluated with the PDF-SYM method instead of the traditional weighted-sum approach. It makes use of the full PDF information of the shear estimators, and does not require weightings on the shear estimators, which can in principle introduce additional systematic biases. This work presents our constraints on $S_8$ and $\Omega_m$ from the shear-shear correlations using the PDF-SYM method. The data we use is from the z-band images of the Dark Energy Camera Legacy Survey (DECaLS), which covers about 10000 deg$^2$ with more than 100 million galaxies. The shear catalog is produced by the FQ method, and well tested on the real data itself with the field-distortion effect. Our main approach is called quasi-2D as we do use the photo-$z$ information of each individual galaxy, but without dividing the galaxies into redshift bins. We mainly use galaxy pairs within the redshift interval between 0.2 and 1.3, and the angular range from $4.7$ to $180$ arcmin. Our analysis yields $S_8=0.762 \pm 0.026$ and $\Omega_m=0.234 \pm 0.075$, with the baryon effects and the intrinsic alignments included. The results are robust against redshift uncertainties. We check the consistency of our results by deriving the cosmological constaints from auto-correlations of $\gamma_1$ and $\gamma_2$ separately, and find that they are consistent with each other, but the constraints from the $\gamma_1$ component is much weaker than that from $\gamma_2$. It implies a much worse data quality of $\gamma_1$, which is likely due to additional shear uncertainties caused by CCD electronics (according to the survey strategy of DECaLS). We also perform a pure 2D analysis, which gives $S_8=0.81^{+0.03}_{-0.04}$ and $\Omega_m=0.25^{+0.06}_{-0.05}$. Our findings demonstrate the potential of the PDF-SYM method for precision cosmology.

Speaker: Zhenjie Liu (Shanghai Jiao Tong University)

5_quasi-2D-Zhenjie-v2.pdf

10:50 AM → 12:30 PM Plasma Astrophysics: Friday

Convener: Brian Reville (MPIK)

10:50 AM Magnetogenesis in a collisionless plasma: from Weibel instability to turbulent dynamo

Astronomical observations suggest pervasive micro-gauss magnetic fields in our Galaxy and in the intracluster medium (ICM) of galaxy clusters. It is widely believed that such dynamically important magnetic fields are produced by plasma dynamos acting upon some "seed"' magnetic fields. However, a complete understanding of this process in a weakly collisional plasma is still lacking. We report a first-principles numerical and theoretical study of plasma dynamo in a fully kinetic framework. By applying an external mechanical force to an initially unmagnetized plasma, we develop a self-consistent treatment of the generation of "seed" magnetic fields, the formation of turbulence, and the inductive amplification of fields by fluctuation turbulent dynamo. The driven large-scale motions in an unmagnetized, weakly collisional plasma are subject to strong phase mixing, which in turn leads to the development of thermal pressure anisotropy. The Weibel instability is then triggered and produces filamentary, micro-scale "seed" magnetic fields. The plasma is thereby magnetized, enabling the stretching and folding of the fields by the plasma motions and the development of pressure-anisotropy instabilities. The scattering of particles off these microscale magnetic fluctuations provides an effective viscosity, impacting the field morphology and turbulence. During this process, the seed fields are further amplified by the fluctuation dynamo until they attain equipartition with the turbulent flow. This work has important implications for magnetogenesis in dilute astrophysical systems by demonstrating that equipartition magnetic fields can be generated from an initially unmagnetized plasma through large-scale turbulent flows.

Speaker: Muni Zhou (Institute for Advanced Study)

Fri1_Texas2023_nomovie.pdf

11:15 AM MHD-PIC Simulations of the Cosmic-ray Gyro-resonant Instabilities

Cosmic-ray (CR) gyro-resonant instabilities represent the key physical mechanism behind CR feedback at macroscopic (e.g., galactic) scales, whose microphysics involves gyro-resonance between the low-energy (GeV) CRs and background MHD waves. Using the MHD-particle-in-cell (MHD-PIC) method, we design a streaming box and an expanding box frameworks to study two flavors of the instabilities, the CR streaming instability and the CR pressure anisotropy instability. Our 1D simulations achieve the steady-state balance between wave growth and damping, as well as between driving CR streaming/anisotropy and isotropization via wave scattering. It allows us to measure the CR transport coefficients from first principles as a function of background environment, which can be eventually incorporated into subgrid prescriptions for studies of CR feedback. These simulations are being generalized to 2D, revealing the importance of oblique waves in CR transport.

Speaker: Xuening Bai (Tsinghua University)

Fri2_CR_Bai.pdf

11:40 AM Ultrafast variability in AGN jets: intermittency and lighthouse effect

Gamma-ray flares from Active Galactic Nuclei (AGN) show substantial variability on ultrafast timescales (i.e. shorter than the light crossing time of the AGN's supermassive black hole). I will show that ultrafast variability is a byproduct of the turbulent dissipation of the jet Poynting flux. Due to the intermittency of the turbulent cascade, the dissipation is concentrated in a set of reconnecting current sheets. Electrons energised by reconnection have a strong pitch angle anisotropy, i.e. their velocity is nearly aligned with the guide magnetic field. Then each current sheet produces a narrow radiation beam, which dominates the emission from the whole jet when it is directed towards the observer. The ultrafast variability is set by the light crossing time of a single current sheet, which is much shorter than the light crossing time of the whole emission region. The predictions of this model are: (i) The bolometric luminosity of ultrafast AGN flares is dominated by the inverse Compton (IC) emission, as the lower energy synchrotron emission is suppressed due to the pitch angle anisotropy. (ii) If the observed luminosity includes a non-flaring component, the variations of the synchrotron luminosity have a small amplitude. (iii) The synchrotron and IC emission are less variable at lower frequencies, as the cooling time of the radiating particles exceeds the light crossing time of the current sheet. Simultaneous multiwavelength observations of ultrafast AGN flares can test these predictions.

Speaker: Emanuele Sobacchi (Istituto Nazionale di Astrofisica)

11:52 AM Magnetic Field Amplification Driven by a Relativistic Shock-Clump Interaction in Collisionless Plasma Systems

Investigations of magnetic field amplification mechanisms at astrophysical shocks are important for understanding of acceleration mechanism of cosmic rays and radiation mechanisms in high-energy astrophysical phenomena. So far, magnetohydrodynamic (MHD) simulations and laboratory experiments have investigated magnetic field amplification in a non-relativistic or mildly relativistic shock propagating through inhomogeneous media. According to their studies, turbulence driven by the interaction between the shock and density fluctuation amplifies the ambient magnetic field in the post-shock region. The turbulent dynamo is thought to be a promising mechanism of magnetic field amplification. However, in collisionless systems, the shocked density fluctuations could easily decay due to particle diffusion because the coulomb mean-free path is much longer than the system size. We investigate - for the first time- the relativistic collisionless shock-clump interaction by means of particle-in-cell (PIC) simulations. We also perform relativistic MHD simulations for the same condition and compared the results between PIC and MHD. In both the PIC and MHD simulations, the shocked clump rapidly decelerates due to relativistic effects. We can derive the deceleration of the shocked clump in an analytic formula. Moreover, in the PIC simulation, particles in the shocked clump escape along the magnetic field line. As a result, the vorticity in the PIC simulations is lower than that in the MHD simulations. Owing to the particle escape and the rapid deceleration, we found that the turbulent dynamo by the shock-clump interaction is not efficient for relativistic collisionless shocks [Tomita et al. 2022].

Speaker: Sara Tomita (Tohoku university)

Fri4_texas2023tomita.pdf

12:04 PM One-dimensional force-free numerical simulations of Alfven waves around a spinning black hole

We performed one-dimensional force-free magnetodynamic numerical simulations of the propagation of Alfven waves along magnetic field lines around a spinning black hole hole to investigate the dynamic process of wave propagation and energy transport with Alfven waves. We considered axisymmetric and stationary magnetosphere and perturbed the background magnetosphere to obtain the linear wave equation for the Alfven wave mode. As shown by the previous study \citep{koide22} with the BTZ coordinates, the Alf\'{e}n wave induces the fast wave. Considering the additional fast magnetosonic wave induced by the Alfven wave, the energy conservation is confirmed.

Speaker: Shinji Koide (Kumamoto University)

12:16 PM Acceleration of plasma ions driven by high-energy lepton flows via the Weibel instability

The interaction of high energy lepton flows with background electron-proton plasma has been investigated with particle-in-cell simulation, focusing on the acceleration processes of background protons due to development of electromagnetic turbulence. Such interaction may be found when plasma jets propagate in the interstellar medium. When an electron-positron beam is injected into the background plasma, the Weibel instability is excited, which soon leads to the development of plasma turbulence. The turbulent electric and magnetic fields accelerate plasma particles via Fermi II type acceleration, where power-law energy spectra are found both for electrons and protons. The accelerated protons provide a dissipative mechanism for the formation of collisionless electrostatic shock waves at later time. Some pre-accelerated protons are further accelerated when passing through the shock wave front. Dependence of proton acceleration on the beam-plasma density ratio and beam energy is investigated. For homogeneous plasma, both acceleration mechanisms are found to be significant; In the case of inhomogeneous plasma, the proton acceleration in the turbulent fields is dominant. The final proton energy increases with the kinetic energy and density of the lepton flow.

Speaker: Zhengming Sheng (Shanghai Jiao Tong University)

Fri5_Sheng-Texas Symposium.pdf

12:30 PM → 1:30 PM Lunch provided

1:30 PM → 2:45 PM Summary

Convener: Prof. Dong Lai (TDLI)

1:30 PM Reports on mini-symposia by conveners

Friday summary.pdf

TXinAZ2025.pdf

1:50 PM Relativistic Astrophysics: Progress, Promise and Prospects

Speaker: Prof. Roger Blandford

231215shanghai.pdf

2:45 PM → 3:45 PM Poster

2:45 PM A multi-zone view on the multi-wavelength emission of blazars

In this work, a time-dependent modeling is developed to study the emission properties of blazars in the low state. Motivated by various observations, we speculate and assume that numerous discrete radiation zones throughout the jet of a blazar contribute to the broadband emission. We model the temporal evolution of the electron spectrum in each emission zone taking into account the injection, cooling and escape of relativistic electrons. By doing so, we are able to calculate the multi-wavelength emission of each radiation zone. The observed emission of a blazar is then the superposition of the emission from all discrete radiation zones. We revisit the multi-wavelength spectral energy distributions, light curves and polarisation under the model, and discuss its potential to reproduce the flat radio spectra, the core-shift phenomena, the minute-scale gamma-ray variability, and the large polarisation-angle swings, which are difficult to explain under the conventional one-zone models simultaneously.

Speaker: Hongbin Tan (Nanjing University)

2:46 PM Star Formation Activity and Cosmic Rays Acceleration in Starburst Galaxies

Starburst Galaxies (SBs) have higher star formation rate and supernova (SN) explosion rate. Therefore, SBs are promising cosmic-rays (CRs) accelerator. Such CRs produced in the birth and death of stars are expected to produce gamma-ray emission. The identification of supernova remnant and the observation of galactic-scale outflow indicate that SN-triggered activities play an important role in CR acceleration in SBs.

Speaker: Ziwei Ou (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

2:47 PM Matching Neutrino-Dark Matter Scattering Limits from Boosted Dark Matter and Neutrino Echo using Supernovae Neutrino Flux

In recent years, there have been limits placed on neutrino-dark matter scattering using the neutrino echo effect and using boosted dark matter detection respectively. In this work, we aim to combine the analysis on both parts by using galactic supernovae neutrino fluxes covering an extended energy range, which shows effects from both phenomena, thereby matching the parameter spaces from the two types of analysis which have been independent from each other previously. This gives us a better understanding of where current limits stand for neutrino-DM scattering, preparing for the next generation astroparticle DM detectors.

Speaker: Miaochen Jin (Harvard University)

2:48 PM Mirage Sources and Large Offsets: Interconnected Phenomena in Asymmetric Diffusion and projection effects

we show that a large asymmetric halo may be mis-identified as multiple mirage sources, and asymmetric diffusion could lead to a very large offset between the injection site and the identified halo. We add background noise into the region of interest and use statistical method as is used by experimentalists to identify the sources. We utilize the concept of asymmetric diffusion to elucidate several observed sources that were previously challenging to interpret. Our model offers intuitive explanations for these observations and has the potential to aid identification of a broad range of sources.

Speaker: Yiwei Bao

2:49 PM A Camera-based Optical Calibration System for Water-based Neutrino Telescopes

The angular resolution and energy threshold of a water-based neutrino telescope are significantly influenced by the level of absorption and scattering experienced by Cherenkov photons in the medium. Unlike glacial ice, the dynamic water environment can lead to changing optical properties within the large detector volume. Therefore, the use of a real-time calibration system among the detector array is necessary. This paper introduces a novel calibration system based on CMOS cameras and steady LED light sources. Its efficient image processing algorithms enable real-time optical measurements. The system is highly suitable for implementation in the future TRIDENT detector. The successful demonstration of this camera system at a depth of 3420m by the T-REX experiment in 2021 further validates its effectiveness.

Speaker: Wei Tian

2:50 PM Shower Reconstruction in TRIDENT

TRopIcal DEep-sea Neutrino Telescope (TRIDENT) is a next-generation neutrino observatory to be located in the South China Sea. With its large instrumented volume, unique position near the equator and use of advanced hybrid digital optical modules (hDOMs), TRIDENT aims to discover multiple astrophysical neutrino sources and probe all-flavor neutrino physics. In contrast to track-like events, shower-like neutrino events have a low rate of background atmospheric muon events. Neutrino telescopes with degree-level angular resolution for shower-type neutrino events would boost source-searching sensitivity and probe neutrino oscillation across astronomical baselines. In this contribution, we present TRIDENT's angular resolution in the reconstruction of shower-like neutrino events from 10 TeV to 1 PeV.

Speaker: Iwan Morton-Blake (Tsung-Dao Lee Institute / Shanghai Jiao Tong University)

2:51 PM Dark Matter Direct Detection with XENONnT: the Latest Result

The XENON project is a multi-stage research program that aims to identify the true nature of dark matter using two-phase liquid xenon time projection chambers of increasing size and sensitivity. The current phase, XENONnT, is operating at the deep underground Laboratori Nazionali del Gran Sasso(LNGS) in Italy. The first science run was performed from May to December 2021. In this talk, I will present the first search for weakly interacting massive particles (WIMPs) using a 1.1 tonne-year exposure of XENONnT data. This exposure featured unprecedentedly low levels of electronegative impurities, and 85Kr and 222Rn background rates. After a blind analysis of the data, no significant excess is observed. Compared to previous XENON results with a comparable exposure, this search improves the sensitivity to WIMPs by a factor of 1.7.

Speaker: Kexin Liu

2:52 PM Variations of Small-scale Cosmic Ray Anisotropies with Time and Energy

The arrival directions of TeV cosmic rays on the sky display an anisotropy at the 0.1 percent level. This anisotropy contains a dipole and higher order multipoles. Small-scale anisotropies should contain important information about the properties of the turbulent magnetic fields in the interstellar medium. These anisotropies have been predicted to vary on a time-scale of a decade at TeV energies. To date, no time variation has been detected. Whether experiments can detect such time variations or not depends on their energy resolutions (△𝐸/𝐸). Finite energy resolutions can result in substantial changes of the anisotropy at small scales. Compared to previous works on this topic, we consider here the effect of the energy resolution on the detectability of time variations. We find that the amplitude of the difference between two instants in time will be smaller than in calculations where the energy resolution is not taken into account. We also study in detail the energy dependence of the small-scale anisotropies. We find that the amplitudes of the observed small-scale anisotropy structures are larger with a better energy resolution.

Speaker: Wenyi Bian (上海交通大学李政道研究所)

2:53 PM Dark Matter Annihilation via Breit-Wigner Enhancement with Heavier Mediator

We propose a new scenario that both the dark matter freeze-out in the early Universe and its possible annihilation for indirect detection around a supermassive black hole are enhanced by a Breit-Wigner resonance. With the mediator mass larger than the total initial dark matter mass, this annihilation is almost forbidden at late times. Thus, the stringent cosmic microwave background and indirect detection constraints do not apply. However, a supermassive black hole can accelerate the dark matter particles to reactivate this resonant annihilation whose subsequent decay to photons leaves a unique signal. The running Fermi-LAT and the future COSI satellites can test this scenario.

Speaker: Yu Cheng

Texas_YuCheng.pdf

2:55 PM Detectability of very-high-energy counterpart of gravitational waves

The joint detection of GW170817 and a short gamma-ray burst (GRB) has provided the first direct evidence that binary neutron star (BNS) merger produces GRB. Recently and unprecedentedly, very-high-energy (~0.1--10 TeV) afterglow emission were reported from a few GRBs (e.g. MAGIC, H.E.S.S. and LHAASO observations), suggesting the prospects of multi-messenger detection of gravitational-wave counterparts with the next-generation gamma-ray detectors. We study GW-TeV joint detectability of BNS merger using a population model prescribing the distribution of common parameters (e.g. energetics, viewing angle) in both gravitational-wave and very-high-energy afterglow emission. We report the expected distributions of observables (distances, orientations, energetics and ambient densities) for detectable events and the joint GW-TeV detection rate for the CTA and LHAASO projects.

Speaker: Haoxiang Lin

2:56 PM Extending JUNO’s Astrophysical Reach with a Low-Energy Multi-Messenger Trigger System

The Jiangmen Underground Neutrino Observatory (JUNO) will be a 20kton liquid scintillator detector, currently under construction in southern China. JUNO will be instrumented with close to 18,000 20-inch photomultiplier tubes (PMTs), possessing the highest photocathode coverage of any kiloton-scale liquid scintillator or Cherenkov detector to date. With its first-rate size, PMT coverage and low-background levels, JUNO will have highly competitive sensitivity to extra-terrestrial MeV-scale neutrinos. To maximise its astrophysical potential, a dedicated multi-messenger (MM) trigger has been developed. The new system will allow for an unprecedented minimum energy threshold of O(10keV), monitoring an extensive energy band of all-flavour neutrinos. The MM trigger will rapidly remove PMT dark noise, filter 14C background events and search in real-time for transient neutrino signals. Upon the detection of an astrophysical neutrino burst, JUNO can communicate with global multi-messenger facilities on a millisecond time scale, allowing for rapid follow-up measurement campaigns across the various detectors.

Speaker: Iwan Morton-Blake (Tsung-Dao Lee Institute / Shanghai Jiao Tong University)

2:57 PM Recent Discoveries of TeV Halos

TeV halos have drawn extensive attention since the first discovery from the HAWC observatory. These huge gamma-ray structures around pulsars provide important information about the particle acceleration and propagation in pulsar-powered systems, and probe the characteristics of the ambient interstellar environments. With HAWC, LHAASO, and other ground-based and space-borne gamma-ray instruments, more TeV halos, more generally, pulsar halos, are discovered and studied at different energies. In this contribution, I will summarize the discoveries of the first TeV halos and discuss the future prospects.

Speaker: Hao Zhou (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

2:58 PM Fast Radio Bursts in the Fireball Paradigm

Fast radio bursts (FRBs) are the brightest radio transients in the universe. Since their unexpected discovery in the 21st century, their extreme nature has become one of the biggest mysteries in astrophysics. FRBs also serve as unique probes of the universe, opening up a new field of FRB cosmology. In 2020, Galactic FRBs were detected originating from magnetar bursts, pinning down one of the origins of FRBs. In this talk, I will explore the mechanisms for transferring energy from the surface of a neutron star to the emission site of FRBs in the fireball paradigm. A fireball expands along magnetic field lines, converting thermal energy to kinetic energy and X-ray bursts. Additionally, the fireball interacts with Alfven waves launched from the surface through parametric instability. I will discuss the implications of these processes for FRBs.

Speaker: Kunihito Ioka (Yukawa Institute for Theoretical Physics, Kyoto University)

3:18 PM The unusually high activity of supermassive black holes is as-sociated with their close binarity

The data of the last 60 years on the programs of long-term multi-frequency monitoring of active galactic nuclei 3C 273 are analyzed. A model is proposed for finding the parameters of close binary systems from supermassive black holes.
It has been established that 3C 273 can be a very massive binary system at the stage of evolution close to merging. Based on the obtained parameters, the characteristics of the gravitational radiation of this system, their lifetime before the merger, as well as the possible observation of 3C 273 using gravitational wave detectors considered.

This work was funded by the RSF, project number 23-22-10032.

Speaker: Alexandr Volvach (CRAO)

3:19 PM A broken universal relation for neutron stars in a scalar-Gauss-Bonnet gravitational theory

Modifying general relativity (GR) with a scalar field is a promising attempt to address issues of dark matter and dark energy in astrophysics and cosmology. It can also generate solutions different from those in GR for compact stars. We study the solutions for neutron stars when gravity is modified by a scalar field coupled with the Gauss-Bonnet invariant, causing the remarkable phenomenon of spontaneous scalarization. In this talk, I will first show the spherical solutions for neutron stars in this theory. Then I will present results on tidal deformability and moment of inertia of the scalarized neutron stars. By investigating tidal deformability and moment of inertia under various equations of state (EOSs) for neutron stars, we find that the relation between tidal deformability and moment of inertia for the scalarized neutron stars is not EOS independent. This is the first time that a broken universal relation for neutron stars is found to our knowledge.

Speaker: Rui Xu (Tsinghua University)

3:20 PM Searching Gravitational-Wave Bursts with Space-Borne Detectors

The millihertz gravitational wave band is expected to be opened by space-borne detectors like TianQin. Various mechanisms can produce short outbursts of gravitational waves, whose actual waveform can be hard to model. In order to identify such gravitational wave bursts and not to misclassify them as noise transients, we proposed a proof-of-principle energy excess method, that utilized the signal-insensitive channel to veto noise transients. We perform a test on simulated data, and for bursts with a signal-to-noise ratio of 20, even with the contamination of noise transient, our methods can reach a detection efficiency of 97.4% under a false alarm rate of once per year. However, more frequent occurrences of noise transients would lower the detection efficiency.

Speaker: Zheng Wu (SUN YAT-SEN UNIVERSITY)

3:21 PM Stability of Compact Stellar Anisotropic Objects in Modified Theory of Gravity

The main objective of this paper is to examine the viability and stability of anisotropic compact stellar objects adopting the Karmarkar condition in energy-momentum squared gravity. For this purpose, we take a static spherical metric in the inner and Schwarzschild spacetime in the outer region of the stars. The values of unknown parameters are found by the observational values of mass and radius of the considered compact stars. We consider a particular model of this theory to investigate the behavior of energy density, pressure components, anisotropy, equation of state parameters and energy bounds in the inner region of the proposed stellar objects. The equilibrium state of the stellar models is examined via the Tolman-Oppenheimer-Volkoff equation and their stability is analyzed by causality condition, Herrera cracking approach and adiabatic index. We find that Karmarkar solutions in this modified theory are physically viable and stable for anisotropic stellar objects.

Speaker: Muhammad Sharif

3:25 PM An Explanation for Overrepresentation of Tidal Disruption Events in Post-starburst Galaxies

Tidal disruption events (TDEs) provide a valuable probe in studying the dynamics of stars in the nuclear environments of galaxies. Recent observations show that TDEs are strongly overrepresented in post-starburst or "green valley" galaxies, although the underlying physical mechanism remains unclear. Considering the possible interaction between stars and active galactic nucleus (AGN) disk, the TDE rates can be greatly changed compared to those in quiescent galactic nuclei. We revisit TDE rates by incorporating an evolving AGN disk within the framework of the "loss cone" theory. We numerically evolve the Fokker-Planck equations by considering the star-disk interactions, in-situ star formation in the unstable region of the outer AGN disk and the1 evolution of accretion process for supermassive black holes (SMBHs). We find that the TDE rates are enhanced by about two orders of magnitude shortly after the AGN transitions into a non-active stage. During this phase, the accumulated stars are rapidly scattered into the loss cone due to the disappearance of the inner standard thin disk. Our results provide an explanation for the overrepresentation of TDEs in post-starburst galaxies.

Speaker: mengye wang

3:25 PM The magnetohydrodynamic-particle-in-cell module in ATHENA ++

We present a new magnetohydrodynamic-particle-in-cell (MHD-PIC) code integrated into the \texttt{Athena++} framework.
It treats energetic particles as in conventional PIC codes while the rest of thermal plasmas are treated as background fluid described by MHD, thus primarily targeting at multi-scale astrophysical problems involving the kinetic physics of the cosmic-rays (CRs).
The code is optimized toward efficient vectorization in interpolation and particle deposits, with excellent parallel scaling.
The code is also compatible with curvi-linear coordinates, static/adaptive mesh refinement, with dynamic load balancing to further enhance multi-scale simulations. In addition, we have implemented a compressing/expanding box framework which allows adiabatic driving of CR pressure anisotropy, as well as the $\delta f$ method that can dramatically reduce Poisson noise in problems where distribution function $f$ is only expected to slightly deviate from the background.
The code performance is demonstrated over a series of benchmark test problems including particle acceleration in non-relativistic parallel shocks. In particular, we measure the CR scattering rate at the saturated state in the balance between the CR gyro-resonance instabilities and ion-neutral damping, from the first princeple, to calibrate the CR feedback effeciency in galaxy evolutions.

Speaker: Xiaochen Sun (Princeton University)

3:42 PM Gravitational waves from magnetar glitches and anti-glitches

In this talk, I will introduce a simple toy model that can simultaneously explain magnetar glitches and anti-glitches. It is based on the idea of mass ejection from the magnetar and how, as a result of the ejecta being trapped by the magnetic field, a time-varying mass quadrupole moment is established leading ultimately to gravitational wave emission. I will use astrophysical arguments to argue that the continuous gravitational waves emitted will be transient (~ few days) in nature and I will comment on whether it will be detectable with future decihertz detectors, like DECIGO and the Big Bang Observer.

Speaker: Garvin Yim (Kavli Institute for Astronomy and Astrophysics, Peking University)

3:43 PM Physical Aspects of Cosmic Parameters in Modified Theory of Gravity

For illustration of the cosmic accelerated expansion of the universe, we will consider the modified Friedmann equations of some torsion-based theory of gravity. In this way, the cosmological parameters such as equation of state, phase-plane, squared speed of sound etc are being developed and examined graphically. For more insights of parameters, power-law forms of scale factor and parameterized forms of Hubble parameter are utilized.

Speaker: Shamaila Rani (Institute for Theoretical Physics and Cosmology, Zhejiang University of Technology, Hangzhou 310023, China)

3:44 PM 21cm signal sensitivity to dark matter decay

The redshifted 21cm signal from the Cosmic Dawn is expected to provide unprecedented insights into early Universe astrophysics and cosmology. In this talk, I will explore how dark matter can heat the intergalactic medium before the first galaxies, leaving a distinctive imprint in the 21cm power spectrum. Using a dedicated Fisher matrix forecast on the sensitivity of the Hydrogen Epoch of Reionization Array (HERA) telescope to dark matter decays, I will show that HERA has the potential to improve current cosmological constraints on the dark matter decay lifetime by up to three orders of magnitude.

Speaker: Yuxiang Qin

3:44 PM Adaptive cancellation of mains power interference in continuous gravitational wave searches with a hidden Markov model

Continuous gravitational wave searches with terrestrial, long-baseline interferometers are hampered by long-lived, narrowband features in the power spectral density of the detector noise, known as lines. Candidate GW signals which overlap spectrally with known lines are typically vetoed. Here we demonstrate a line subtraction method based on adaptive noise cancellation, using a recursive least squares algorithm, a common approach in electrical engineering applications such as audio and biomedical signal processing. We validate the line subtraction method by combining it with a hidden Markov model, a standard continuous wave search tool, to detect a synthetic continuous wave signal with an unknown and randomly wandering frequency which overlaps with the strong mains power line at $60 \, {\rm Hz}$ in the Laser Interferometer Gravitational Wave Observatory. The performance of the line subtraction method with respect to the characteristics of the 60 Hz line and the control parameters of the recursive least squares algorithm is quantified in terms of receiver operating characteristic curves.

Speaker: Dr Tom Kimpson (University of Melbourne)

3:44 PM An Enigmatic PeVatron in an Area around HII Region G35.6−0.5

It is difficult to identify hadronic PeVatrons (the PeV particle accelerator) from the ultra-high-energy (UHE, $E$ > 100 TeV) gamma-ray sources, which is however crucial in revealing the origin of cosmic rays. As an endeavor in this regard, we focus in this work on the UHE gamma-ray source 1LHAASO J1857+0203u, which may be associated with supernova remnant (SNR) G35.6−0.4 and H II region G35.6−0.5. We analyze the LHAASO WCDA and KM2A data, and report the point-like nature with a significance of 10.1$\sigma$ above 100 TeV. While in the energy range of 1−30 TeV, it shows an extension of $r_{39}=0.18^\circ$. The spectra measured by WCDA and KM2A can be smoothly connected, with power-law spectral indexes of $\sim$2.5 and $\sim$3.2, respectively. Given the low mass of the environmental molecular clouds, it is unlikely that the TeV gamma-ray emissions arise from the clouds illuminated by the protons escaped from SNR G35.6−0.4. In the scenario that HII region G35.6−0.5 can accelerate particles to the UHE band, the observed GeV-TeV gamma-ray emission could be well explained by a hadronic model with a power-law spectral index of $\sim$2.0 and a cutoff energy of $\sim$260 TeV. However, a pulsar-wind-nebula origin cannot be ruled out.

Speaker: Ms Wenjuan Zhong (Nanjing University)

3:44 PM An Investigation of state changes of PSR J2021+4026 and Vela pulsar

We report on long-term evolution of gamma-ray flux and spin-down rate of the two bright gamma-ray pulsars,PSR J2021+4026 and Vela (PSR B0833-45). PSR J2021+4026 shows repeated state changes in gamma-ray flux and spin-down rate. We report two new state changes, one from a low gamma-ray flux to a high flux that occurred around MJD 58910 and another one from high to low flux that occurred around MJD 59510. We find that the flux changes associted with these two new state changes are smaller than those determined in the previous events, and the waiting time ofthe new state change from the high gamma-ray flux to low gamma-ray flux is significantly shorter than previous events.The waiting timescale of the quasi-periodic state changes is similar to the waiting timescale of the glitch events of the Vela pulsar, suggesting that the state change of PSR J2021+4026 may be related to a glitch. For the Vela pulsar, the flux of the radio pulses briefly decreased around the 2016 glitch, suggesting that the glitch may have affected the structure of the magnetosphere. Nevertheless, we could not find any significant change of the gamma-ray emission properties using 15 years of Fermi-LAT data. Our results provide additional insights into the relationship between glitches and changes to the gamma-ray emission in pulsars.

Speakers: Huihui Wang (中山大学), Mr Jumpei Takata (Huazhong university of Science and Technology), Mr Thomas Tam (Sun Yat-sen University)

3:44 PM An overview of the instrument, observations and preliminary results of CONCERTO

Using the integrated emission from unresolved sources, line intensity mapping (LIM) provides a new observational window to measure the large-scale structure in the Universe from present times to the high redshift epoch of reionisation. CONCERTO (CarbON CII line in post-rEionisation and ReionisaTiOn epoch) is a low-resolution spectrometer based on the Lumped Element Kinetic Inductance Detectors (LEKID) technology, aimed at carrying out unprecedented research in star formation histories and large-scale structure via line intensity mapping of the [CII] line and galaxies clusters physics via tSZ effect. CONCERTO operates at 130 - 310 GHz and has unique capabilities in fast dual-band spectral mapping at tens arcsecond resolution and 18 arcminutes instantaneous field-of-view. The CONCERTO was installed at the 12-meters APEX telescope in Chile and the scientific observation started in July 2021. We have developed a data-processing pipeline to go from raw data to continuum and spectroscopic data cubes, including data reading and raw-data calibrating, bad KIDs masking, flat-field normalization, opacity correction, correlated noise subtraction and map projection. In this talk, I will present an overview of the instrument, observations and preliminary results of CONCERTO.

Speaker: Wenkai Hu

3:44 PM Angular power spectrum of the TeV cosmic ray anisotropy

Propagating individual cosmic rays in synthetic three-dimensional Kolmogorov turbulence, we calculate their anisotropy at the location of an observer. These are the first calculations of the cosmic ray anisotropy down to TeV energies for values of the turbulence coherence length that are realistic for the interstellar medium. We calculate the power spectrum 𝐶𝑙, of the cosmic ray anisotropy for different observer locations, and compare with observations. We also decompose the anisotropy onto spherical harmonics, and show that an important distinction should be made between higher order multipoles that are aligned with the local direction of the magnetic field at the observer’s location, and those that are not.

Speaker: Wenyi Bian (上海交通大学李政道研究所)

3:44 PM Cascade Radiations of $e^\pm$ from $\gamma\gamma$-annihilation process as an extra component of the Early Optical/X-Ray Afterglows of Gamma-Ray Bursts

Chromatic break and/or plateau observed in the early optical and X-ray afterglow light curves challenge the conventional external shock models of gamma-ray bursts (GRBs). Detection of TeV gamma-ray afterglows indicates strong gamma-ray production within the afterglow jets.
We investigate the cascade radiations of the $e^\pm$ production via the $\gamma\gamma$ interaction in the jets. Our numerical calculations show that the cascade synchrotron emission can make a significant contribution to the early optical/X-ray afterglows. The combination of the primary and cascade emission fluxes can shape a chromatic break and/or plateau in the early optical/X-ray light curves, depending on the jet properties. Applying our model to GRBs 050801 and 080310, we found that their optical plateaus and the late X-ray/optical light curves can be explained with our model in reasonable parameter values. We suggest that such a chromatic optical plateau could be a signature of strong $e^\pm$ production in GRB afterglow jets. The TeV gamma-ray flux of such kind GRBs should be significantly reduced, hence tends to be detectable for those GRBs that have a single power-law decaying optical afterglow light curve.

Speaker: Xiaoli Huang (Guizhou Normal University)

3:44 PM Coherent Cherenkov Radiation by Bunches in Fast Radio Bursts

Fast radio bursts (FRBs) are extragalactic radio transients with extremely high brightness temperature, which strongly suggests the presence of coherent emission mechanisms. In this study, we introduce a novel radiation mechanism for FRBs involving coherent Cherenkov radiation (ChR) emitted by bunched particles that may originate within the magnetosphere of a magnetar. We assume that some relativistic particles are emitted from the polar cap of a magnetar and move along magnetic field lines through a charge-separated magnetic plasma, emitting coherent ChR along their trajectory. The crucial condition for ChR to occur is that the refractive index of the plasma medium, denoted as $n_r$, must satisfy the condition $n_r^2 > 1$. We conduct comprehensive calculations to determine various characteristics of ChR, including its characteristic frequency, emission power, required parallel electric field, and coherence factor. Notably, our proposed bunched coherent ChR mechanism has the remarkable advantage of generating a narrower-band spectrum. Furthermore, a frequency downward drifting pattern, and $\sim100\%$ linearly polarized emission can be predicted within the framework of this emission mechanism.

Speaker: 泽南 刘 (南京大学)

3:44 PM Constraining the acceleration of moving binary black holes with gravitational wave

Binary black holes (BBHs) are among the most important sources of gravitational waves (GWs). Recent studies suggest that BBHs may form and merge in the vicinity of supermassive black holes (SMBHs), leading to overestimated black hole masses due to gravitational and Doppler redshift. A distinctive characteristic of these GW sources is their acceleration around the SMBH, allowing for their identification through the constraint of this acceleration using GW signals. In this study, GW sources that deviate from the predictions of general relativity in the inspiral-merger-ringdown (IMR) consistency test are considered as potential candidates for acceleration. We construct the accelerated waveform by accounting for relativistic effects, including Doppler shift, aberration, and magnification resulting from the gravitational lensing effect of the SMBH. Through our analysis of detectability, we find that the additional effects beyond Doppler shift can be observed with next-generation ground-based interferometers. Accounting for these effects enhances the probability of detecting the accelerating sources.

Speaker: Xinmiao Zhao (Peking University)

3:44 PM Constraining the Propagation Speed of Gravitational Waves with White Dwarf Binaries

Ultra-compact white dwarf binaries are strong sources of gravitational radiation, and the galactic white dwarf binaries are major sources for the space-based laser interferometer gravitational wave observatory LISA. Some of these binary systems will also be visible through electromagnetic observations, making them multi-messenger astronomy sources. By comparing the phase differences between gravitational and electromagnetic waves, one can place upper bounds on the speed of gravitational waves. In this project, we proposed to simulate white dwarf populations in the Milky way using population synthesis code COSMIC, to statistically assess the potential of multi-messenger sources to constrain the speed of gravitational waves using LISA and electromagnetic observations.

Speaker: Yiqing Guo (Northwestern University)

3:44 PM Constraining the SSC Model of GRB 221009A via Spectral Energy Distribution

GRB 221009A is an exceptionally bright and relatively nearby event, displaying a substantial abundance of very high energy (VHE) photons as observed by the two LHAASO instruments: WCDA and KM2A. The prevailing model attributes the origin of these VHE photons to synchrotron self-Compton (SSC) radiation arising from external shocks within the afterglow of the burst. Nevertheless, when gamma photons traverse the vast cosmic distances to reach Earth, their flux becomes attenuated owing to the absorption by the extragalactic background light (EBL), particularly at energies surpassing the TeV scale. In this context, the axion-like particle (ALP) theory emerges as a potential explanation to resolve this problem. In this study, in conjunction with the ALP theory, we aim to employ SSC Model in the early stages of afterglow to explain the spectral energy distribution observed by the WCDA and KM2A instruments. We impose the constraints on the parameters of the SSC radiation model, thereby enhancing our understanding of the physics of GRB 221009A.

Speaker: He-Wen Yang (Sun Yat-sen University)

3:44 PM Cosmic ray flux at the knee, and diffuse gamma-ray emission at Very High Energies

The origin of the knee in the cosmic ray (CR) spectrum is still unknown after 65 years of studies. Here, within the framework of anisotropic CR diffusion models, we show that the knee is a time-dependent feature, and that the flux in this region contains major contributions from one or a few nearby recent CR sources. We calculate the propagation of CRs in the Jansson-Farrar galactic magnetic field model, after injecting them at discrete sources in the disc of the Galaxy. Anisotropic diffusion plays a key role in reconciling the large diffusion coefficient required for CR escape from the Galaxy with the measured value of the Galactic magnetic field. The main difference with the isotropic diffusion case is a significant reduction of the number of sources that contribute to the CR flux in any given location in the Galaxy. As a result, few sources dominate the local flux at the knee. We then calculate the resulting diffuse gamma-ray emission at Very High Energies, and compare our results to the data of gamma-ray observatories.

Speaker: Gwenael Giacinti (TDLI & SJTU)

3:44 PM Could the TeV emission of starburst galaxies originate from pulsar wind nebulae?

While the GeV $\gamma$-rays emission of starburst galaxies (SBG) is commonly thought to arise from hadronic interactions between accelerated cosmic rays and interstellar gas, the origin of the TeV $\gamma$-ray emission is more uncertain. One possibility is that a population of pulsar wind nebulae (PWNe) in these galaxies could be responsible for the TeV $\gamma$-ray emission. In this work, we first synthesize a PWNe population in the Milky Way, and assessed their contribution to the $\gamma$-ray emission of the Galaxy, using a time-dependent model to calculate the evolution of the PWN population. Such synthetic PWN population can reproduce the flux distribution of identified PWNe in the Milky Way given a distribution of the initial state of the pulsar population. We then apply it to starburst galaxies and quantitatively calculate the spectral energy distribution of all PWNe in the SBG NGC 253 and M82. We propose that TeV $\gamma$-ray emission in starburst galaxies can be dominated by PWNe for a wide range of parameter space. The energetic argument requires that $\eta_e \times v_{\rm SN} > 0.01 {\rm yr}^{-1}$, where $\eta_e$ is the fraction the spin-down energy going to electrons and $v_{\rm SN}$ is the supernova rate. By requiring the synchrotron emission flux of all PWNe in the galaxy not exceeding the hard X-ray measurement of NGC 253, we constrain the initial magnetic field strength of PWNe to be $< 400 \mu$G. Future observations at higher energies with LHAASO or next-generation neutrino observatory IceCube-Gen2 will help us to understand better the origin of the TeV $\gamma$-rays emission in SBGs.

Speaker: Xiao-Bin Chen (Nanjing University)

3:44 PM Data gaps inpainting for space-based gravitational-wave detectors

Data gaps in space-borne gravitational wave detectors, arising from factors such as micrometeorite collisions or hardware malfunctions, pose a significant challenge in gravitational wave data processing. The milli-Hertz observation frequency range and possible day-scale occurance rate for the gap makes the appropriate estimating of the noise property, and correspondingly the following data analysis challenging. To mitigate the impact of data gaps in gravitational wave data, we develop an inpainting algorithm to fill in the data gap. This allows preserves data continuity without adding additional information of matched-filtering and likelihood. We demonstrate the efficacy of this algorithm with a simulated TianQin observation data for massive black hole mergers, showing that the inpainting allows correct analysis of the massive black hole properties as if the gap almost does not exist.

Speaker: Lu Wang (TianQin Research Center for Gravitational Physics Sun Yat-sen University (Zhuhai Campus))

3:44 PM Detection and characterization of gravitational waves of stellar-mass binary black holes for LISA

Future space-based laser interferometric detectors will be able to observe gravitational waves (GWs) generated during the inspiral phase of stellar-mass binary black holes (SmBBHs), which contain a wealth of important physical information concerning astrophysical formation channels and fundamental physics constraints. However, the detection and characterization of GWs from these SmBBHs remains one of the major challenges in data analysis. In this work, we construct a data analysis pipeline using the semi-coherence method and Particle Swarm Optimization (PSO), while accelerating the analysis using the frequency domain response of the detector and parallel computation based on the Graphics Processing Unit (GPU). As a result, we can perform global searches for the GW signals of SmBBH and estimate the parameters in a reasonable time for the simulated data for the Laser Interferometer Space Antenna (LISA). We test the performance of our pipeline on simulated data sets containing realistic noise and demonstrate that, for GW signals with signal-to-noise ratios (SNRs) in the range of 15 to 20, LISA can accurately determine most of the parameters, including the orbital eccentricity. In this talk, we will present the fundamentals of our pipeline, its implementation and robustness, and provide new insights into the future of space-based GW detection and parameter estimation.

Speaker: Yao Fu (Huazhong University of Science and Technology)

3:44 PM Detection and parameter estimation of ringdown signals using a pulsar timing array

Gravitational wave (GW) searches using a pulsar timing array (PTA) are typically limited to the GW frequency $\le 4 \times 10^{-7}$ Hz, due to the average observational cadence of 2 weeks for a single pulsar. By taking advantage of asynchronous observations of multiple pulsars, PTA has the potential to detect GW signals with frequencies higher than the Nyquist frequency of a single pulsar. An example of such a signal is the GWs from the ringdown phase of merging supermassive binary black holes (SMBHBs). In this work, we propose a likelihood-based method for detecting ringdown signals using a PTA. We consider only a single mode, i.e., the $(2,2)$ mode, to demonstrate our method. The ringdown waveform is modeled as an exponentially decaying sinusoidal signal, and its parameters are divided into extrinsic parameters and intrinsic parameters. The former ones are determined analytically, and the latter ones are determined numerically using particle swarm optimization (PSO). We show that for the optimal signal-to-noise ratio (SNR) $\rho = 10$ scenario, which corresponds, for example, to a SMBHB with chirp mass $M_c=10^{10} M_\odot$ at a distance $D = 300$ Mpc, it has a detection probability of 99% if the threshold is set to be the highest detection statistic value obtained with the $\rho = 0$. For the same SNR, the parameter estimation errors are: $\sigma_\alpha \approx 4.8607^\circ$, $\sigma_\delta \approx 4.2476^\circ$ for sky localization, $\sigma_\omega \approx 7.3198$ rad/yr for angular frequency, $\sigma_\tau \approx 0.009838$ yr for ringdown timescale, and $\sigma_{t_0} \approx 9.54$ hr for the signal start time.

Speaker: Xuan Tao (Huazhong University of Science and Technology)

poster_shanghai.pdf

3:44 PM Development of a lake array proposal for SWGO

The Southern Wide-field Gamma-ray Observatory (SWGO) is a proposed next-generation gamma-ray survey experiment that will cover the southern sky with high sensitivity and a wide field of view. It will be built in South America to complement HAWC and LHAASO in the Northern Hemisphere. We designed a lake array proposal for SWGO to record particles from extensive air showers initiated by high energy gamma-rays. The proposed lake array would consist of two types of detectors: surface detectors and muon detectors. Surface detectors will be placed on the lake for the detection of electromagnetic particles. They are small tanks filled with water and equipped with a photomultiplier tube (PMT) at the bottom. Muon detectors will be deployed underwater, where lake water will be a natural filter to absorb electromagnetic components while allowing the measurement of muon particles. A lake array is being proposed for SWGO motivated by some potential advantages over ground-based arrays, such as lower cost, fewer constraints on the detector shape, and electromagnetic component rejection for muon detectors, which create more possibilities to optimize detectors and the array. A number of technological solutions are being proposed for the implementation of SWGO, including both lake- and ground-based arrays, and a final decision on the adopted technology is expected for 2024, with the conclusion of the project's R&D phase.

Speaker: Hao Zhou (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

3:44 PM Dynamical energy dissipation of relativistic magnetic jets

Relativistic outflows or jets with more than 99% of the light speed emerge in pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei. Such relativistic jets are thought to be launched through magnetic processes, which implies magnetically dominated outflows. However, a multi-wavelength spectrum suggests that jets must be kinetically dominated at the gamma-ray emission region. This means the magnetic energy should dissipate into the thermal energy while propagation. Although the traditional shock dissipation mechanism so-called internal shock is thought to be inefficient for magnetically dominated ejecta, a kinetically dominated matter between ejecta may play an important role in magnetic energy dissipation by shock waves.

We demonstrate the efficient internal shock dissipation through the multiple interactions between magnetically dominated relativistic ejecta with kinetically dominated winds by performing our spherically symmetrical 1-Dimensional Special Relativistic Magneto-HydroDynamic (1D SRMHD) simulation code with adaptive mesh refinement. Our numerical results show that almost 10% of the magnetic energy in the ejecta can be converted into the thermal energy of the relativistic and low-magnetized outflows via shocks in the rarefaction waves or the winds. Such hot and less magnetized outflows are relevant for observed non-thermal emissions in blazars or gamma-ray bursts.

Speaker: Yo Kusafuka (ICRR, The University of Tokyo)

poster_kusafuka.pdf

3:44 PM Dynamical tidal Love numbers of Kerr-like compact objects

We develop a framework to compute the tidal response of a Kerr-like compact object in terms of its reflectivity, compactness, and spin, both in the static and the frequency-dependent case. Here we focus on the low-frequency regime, which can be solved fully analytically. We highlight some remarkable novel features, in particular: i) Even in the zero-frequency limit, the tidal Love numbers (TLNs) depend on the linear-in-frequency dependence of the object's reflectivity in a nontrivial way. ii) Intriguingly, the static limit of the frequency-dependent TLNs is discontinuous, therefore the static TLNs differ from the static limit of the (phenomenologically more interesting) frequency-dependent TLNs. This shows that earlier findings regarding the static TLNs of ultracompact objects correspond to a measure-zero region in the parameter space, though the logarithmic behavior of the TLNs in the black hole limit is retained. iii) In the non-rotating case, the TLNs generically vanish in the zero-frequency limit (just like for a black hole), except when the reflectivity is R=1+O(Mω), in which case they vanish with a model-dependent scaling, which is generically logarithmic, in the black-hole limit. The TLNs initially grow with frequency, for any nonzero reflectivity, and then display oscillations and resonances tied up with the quasi-normal modes of the object. iv) For rotating compact objects, the TLNs decrease when the reflectivity decreases or the rotation parameter increases. Our results lay the theoretical groundwork to develop model-independent tests of the nature of compact objects using tidal effects in gravitational-wave signals.

Speaker: Sumanta Chakraborty (Indian Association for the Cultivation of Science)

3:44 PM Effects of spin-orbit coupling on gravitational waveforms from a triaxial non-aligned neutron star in a binary system

Spinning neutron stars (NSs) can emit continuous gravitational waves (GWs) that carry a wealth of information about the compact object. If such a signal is detected, it will provide us with new insight into the physical properties of matter under extreme conditions. According to binary population synthesis simulations, future space-based GW detectors, such as LISA and TianQin, can potentially detect some double NSs in tight binaries with orbital periods shorter than 10 minutes. The possibility of a successful directed search for continuous GWs from the spinning NS in such a binary system identified by LISA/TianQin will be significantly increased with the proposed next-generation ground-based GW observatories, such as Cosmic Explorer and Einstein Telescope. Searching for continuous GWs from such a tight binary system requires highly accurate waveform templates that account for the interaction of the NS with its companion. In this spirit, we derive analytic approximations that describe the GWs emitted by a triaxial non-aligned NS in a binary system in which the effects of spin-orbit coupling have been incorporated. The difference with the widely used waveform for the isolated NS is estimated and the parameter estimation accuracy of an example signal using Cosmic Explorer is calculated. For a typical tight double NS system with a 6 min orbital period, the angular frequency correction of the spinning NS in this binary due to spin precession is $\sim 10^{-6}~{\rm Hz}$, which is in the same order of magnitude as the angular frequency of orbital precession. The fitting factor between the waveforms with and without spin precession will drop to less than 0.97 after a few days ($\sim 10^5~{\rm s}$). We find that spin-orbit coupling has the potential to improve the accuracy of parameter estimation, especially for the binary inclination angle and spin precession cone opening angle, by up to 3 orders of magnitude.

Speaker: Wen-Fan Feng

FengWF_Texas_Poster.pdf

3:44 PM Enhanced detectability of gravitationally lensed gravitational waves by spinless black holes with aLIGO

We investigate the detectability of GWs that have been lensed by a spinless stellar-mass BH. By numerically solving the full relativistic linear wave equation in the spacetime of a Schwarzschild BH, we find that the strong gravity can create unique signals in the lensed waveform, particularly during the merger and ringdown stages. The differences in terms of fitting factor between the lensed waveform and best-fitted unlensed GR template with spin-precessing and higher-order multipoles are greater than $5\%$ for the lens BH mass within $70 M_\odot \lt M_\mathrm{lens} \lt 133 M_\odot$ under aLIGO's sensitivity. This is up to 5 times more detectable than previous analyses based on the weak field approximation. Based on Bayesian inference, the lensing feature can be distinguished with a signal-to-noise ratio of 12~19, which is attainable for aLIGO.

Speaker: Chengjiang Yin (Nanjing University)

3:44 PM Flares from stars crossing active galactic nuclei disks on low-inclination orbits

The origin of the recently discovered new class of transients, X-ray quasi-periodic eruptions (QPEs), remains a puzzle. Due to their periodicity and association with tidal disruption events and active galactic nuclei (AGN), it is natural to relate these eruptions to stars or compact objects in tight orbits around supermassive black holes. In our work, we predict the properties of emission from bow shocks produced by stars crossing AGN disks and compare them to the observed properties of QPEs. We find that when a star's orbit is retrograde and has a low inclination with respect to the AGN disk and the star is massive, the breakout emission from the bow shock can explain the observed duration and X-ray luminosity of QPEs. This model can further explain various observed features of QPEs, such as their complex luminosity evolution, the modulation of the luminosity and the period, the evolution of the hardness ratio, and the preference of the central SMBHs to have low masses. I will further discuss the formation scenario of tight stellar orbits and advantages of our model against others.

Speaker: Hiromichi Tagawa (Shanghai Astronomical Observatory)

3:44 PM Forbidden Dark Matter Combusted Around Supermassive Black Hole

The forbidden dark matter cannot annihilate into heavier partner or SM particles by definition at the late stage of the cosmological evolution. We