Simulations of gamma-ray burst afterglows with a relativistic kinetic code

Abstract

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p> <span style="font-size: 9.000000pt; font-family: 'Helvetica'">Aims. </span><span style="font-size: 9.000000pt; font-family: 'Times'">This paper introduces a kinetic code that simulates gamma-ray burst (GRB) afterglow emission from the external forward shock and presents examples of some of its applications. One interesting research topic discussed in the paper is the high-energy radiation produced by Compton scattering of the prompt GRB photons against the shock-accelerated electrons. The di</span><span style="font-size: 9.000000pt; font-family: 'rtxr'">ff</span><span style="font-size: 9.000000pt; font-family: 'Times'">erence between the forward shock emission in a wind-type and a constant-density medium is also studied, and the emission due to Maxwellian electron injection is compared to the case with pure power-law electrons. </span></p> <p> <span style="font-size: 9.000000pt; font-family: 'Helvetica'">Methods. </span><span style="font-size: 9.000000pt; font-family: 'Times'">The code calculates the time-evolving photon and electron distributions in the emission region by solving the relativistic ki- netic equations for each particle species. For the first time, the full relativistic equations for synchrotron emission</span><span style="font-size: 9.000000pt; font-family: 'rtxr'">/</span><span style="font-size: 9.000000pt; font-family: 'Times'">absorption, Compton scattering, and pair production</span><span style="font-size: 9.000000pt; font-family: 'rtxr'">/</span><span style="font-size: 9.000000pt; font-family: 'Times'">annihilation were applied to model the forward shock emission. The synchrotron self-absorption ther- malization mechanism, which shapes the low-energy end of the electron distribution, was also included in the electron equation. </span><span style="font-size: 9.000000pt; font-family: 'Helvetica'">Results. </span><span style="font-size: 9.000000pt; font-family: 'Times'">The simulation results indicate that inverse Compton scattering of the prompt GRB photons can produce a luminous </span><span style="font-size: 9.000000pt; font-family: 'txsya'">􏰀</span><span style="font-size: 9.000000pt; font-family: 'Times'">TeV emission component, even when pair production in the emission region is taken into account. This very high-energy radiation may be observable in low-redshift GRBs. The test simulations also show that the low-energy end of a pure power-law distribution of electrons can thermalize owing to synchrotron self-absorption in a wind-type environment, but without an observable impact on the radiation spectrum. Moreover, a flattening in the forward shock X-ray light curve may be expected when the electron injection function is assumed to be purely Maxwellian instead of a power law. The flux during such a flattening is likely to be lower than the </span><span style="font-size: 9.000000pt; font-family: 'Times'; font-style: italic">Swift</span><span style="font-size: 9.000000pt; font-family: 'rtxr'">/</span><span style="font-size: 9.000000pt; font-family: 'Times'">XRT sensitivity in the case of a constant-density external medium, but a wind environment may result in a higher flux during the shallow decay. </span></p> </div> </div> </div> <p> &nbsp;</p>