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...
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...
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...
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...
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...
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...
The recent discovery of pulsating ultraluminous X-ray sources (ULXs) shows that the apparent luminosity of accreting magnetised neutron stars - X-ray pulsars (XRPs) - can exceed the Eddington luminosity by a factor of 100s. The relation between the actual and apparent luminosity is a key ingredient in theoretical models of ULXs, but it is still under debate. It is expected that extreme...
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...
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...
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...
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)...
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...
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...
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...
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...
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...
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...
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...
To introduce work on the spin of black hole candidate 4u 1543-47. The data used in work is of the outburst during 2021.
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...
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...
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...
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...
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, ...
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...
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...
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...
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...
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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 ...
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...
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 $\rightarrow$...
4U 1820−30 is a persistent ultra-compact X-ray binary (XRB) (orbital period of only 11 mins) harbouring a neutron star (NS) and a highly evolved companion star. Throughout its ∼170–180 d super-orbital accretion cycle, the system evolves between phases of high and low X-ray modes, driving dramatic changes in the accretion disk and the jets. In this recently published work (Marino et al., 2023,...
Accretion flows onto a black hole (BH) has to be transonic and transrelativistic. In such wide range in space and temperature, the flow far away from the BH is subsonic and non relativistic and close to the BH it is hot and relativistic. Such a range cannot be described a fixed adiabatic index, equation of state (EoS). An approximate but an accurate EoS was proposed few years ago by...
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...
