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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
