arXiv subjects

Edison Liang

Publications and source records attributed to Edison Liang.

43 records · Page 3Linked to original sources

arXiv2005

Radiative Effects on Particle Acceleration in Electromagnetic Dominated Outflows

Plasma outflows from gamma-ray bursts (GRB), pulsar winds, relativistic jets, and ultra-intense laser targets radiate high energy photons. However, radiation damping is ignored in conventional PIC simulations. In this letter, we study the radiation damping effect on particle acceleration via Poynting fluxes in two-and-half-dimensional particle-in-cell (PIC) plasma simulation of electron-positron plasmas. Radiation damping force is self-consistently calculated for each particle and reduces the net acceleration force. The emitted radiation is peaked within a few degrees from the direction of Poynting flux and strongly linear-polarized.

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arXiv2003

Repeated Bifurcation of Relativistic Magnetic Pulse and Cosmic Gamma-Ray Bursts

The diverse and complex light curves of gamma-ray bursts (GRBs) remain an outstanding astrophysical mystery. Here we report the results of 2-1/2-dimensional particle-in-cell (PIC) simulations of the relativistic expansion of magnetized electron-positron plasmas. When the simulation is carried to >150 light-crossing time of the initial plasma, the plasma pulse reproduces many of the GRB features. Remarkably, the plasma pulse bifurcates repeatedly, leading to a complex, multi-peak structure at late times, resembling GRB profiles.

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arXiv2003

Parameter study of the diamagnetic relativistic pulse accelerator (DRPA) in slab geometry I: Dependence on initial frequency ratio and slab width

Two-and-a-half-dimensional particle-in-cell plasma simulations are used to study the particle energization in expanding magnetized electron-positron plasmas with slab geometry. When the magnetized relativistic plasma with high temperature (initial electron and positron temperature are $k_{B}T_{e}=k_{B}T_{p}=5MeV$) is expanding into a vacuum, the electromagnetic (EM) pulse with large amplitude is formed and the surface plasma particles are efficiently accelerated in the forward direction owing to the energy conversion from the EM field to the plasma particles. We find that the behavior of the DRPA (Diamagnetic Relativistic Pulse Accelerator) depends strongly on the ratio of the electron plasma frequency to the cyclotron frequency $ω_{pe}/Ω_{e}$ and the initial plasma thickness. In the high $ω_{pe}/Ω_{e}$ case, the EM pulse is rapidly damped and the plasma diffuses uniformly without forming density peaks because the initial thermal energy of the plasma is much larger than the field energy. On the contrary, in the low $ω_{pe}/Ω_{e}$ case, the field energy becomes large enough to energize all the plasma particles, which are confined in the EM pulse and efficiently accelerated to ultrarelativistic energies. We also find that a thicker initial plasma increases the maximum energy of the accelerated particles.

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arXiv2003

Charge separation effects in magnetized electron-ion plasma expansion into a vacuum

Charge separation effects in the expansion of magnetized relativistic electron-ion plasmas into a vacuum are examined using 2-1/2-dimensional particle-in-cell plasma simulations. The electrostatic field at the plasma surface decelerates electrons and accelerates ions. A fraction of the surface electrons are trapped and accelerated by the pondermotive force of the propagating electromagnetic pulse, a mechanism we call the DRPA (diamagnetic relativistic pulse accelerator). This charge separation is enhanced as the initial plasma temperature is decreased. The overall energy gain of the plasma particles through the expansion strongly depends on the initial plasma temperature. Moreover, the electrons become relatively less energized and the ions more energized as the plasma temperature decreases.

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arXiv2003

Search for Relativistic Curvature Effects in Gamma-Ray Burst Pulses

We analyze the time profiles of individual gamma-ray burst (GRB) pulses, that are longer than 2 s, by modelling them with analytical functions that are based empirical descriptions of GRB spectral evolution. These analytical profiles are independent of the emission mechanism and can be used to model both the rise and decay profiles Using this method, we have studied a sample of 77 individual GRB pulses, allowing us to examine the fluence, pulse width, asymmetry, and rise and decay power-law distributions. We find that the rise phase is best modelled with a power law of average index $r = 1.31 \pm 0.11$ and that the average decay phase has an index o.f $d = 2.39 \pm 0.12$. We also find that the ratio between the rise and decay times (the pulse asymmetry) exhibited by the GRB pulse shape has an average value of 0.47 which varies little from pulse to pulse and is independent of pulse duration or intensity. We compare these parameters with those predicted to occur if individual pulse shapes are created purely by relativistic curvature effects in the context of the fireball model, a process that makes specific predictions about the shape of GRB pulses. The decay index distribution obtained from our sample shows that the average GRB pulse fades faster than the value predicted by curvature effects, with only 39% of our sample being consistent with the curvature model. We discuss several refinements of the relativistic curvature scenario that could naturally account for these observed deviations.

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arXiv2003

Particle Energization in an Expanding Magnetized Relativistic Plasma

Using a 2-1/2-dimensional particle-in-cell (PIC) code to simulate the relativistic expansion of a magnetized collisionless plasma into a vacuum, we report a new mechanism in which the magnetic energy is efficiently converted into the directed kinetic energy of a small fraction of surface particles. We study this mechanism for both electron-positron and electron-ion (mi/me=100, me is the electron rest mass) plasmas. For the electron-positron case the pairs can be accelerated to ultra-relativistic energies. For electron-ion plasmas most of the energy gain goes to the ions.

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arXiv1996

Gamma-rays from Galactic Black Hole Candidates with Stochastic Particle Acceleration

We consider stochastic particle acceleration in plasmas around stellar mass black holes to explain the emissions above 1 MeV from Galactic black hole candidates. We show that for certain parameter regimes, electrons can overcome Coulomb losses and be accelerated beyond the thermal distribution to form a new population, whose distribution is broad and usually not a power law; the peak energy of the distribution is determined by the balance between acceleration and cooling, with particles piling up around it. Radiation by inverse Compton scattering off the thermal (from background) and non-thermal (produced by acceleration) particles can in principle explain the hard X-ray to gamma-ray emissions from black hole candidates. We present model fits of Cyg X-1 and GRO J0422 in 50 keV -- 5 MeV region observed with OSSE and COMPTEL.

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