2001/02/28 by T. P. Downes, P. Duffy, S. S. Komissarov +1
Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #Pulsars and Gravitational Waves Research #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2002.05282.x
published as MNRAS Vol 322 (2002), 144 · 12 pages, 10 figures, accepted for publication in MNRAS. Expanded discussion in section 5, more tests of the code, and other minor changes
arxiv created 2002/01/22 · openalex publication_date 2002/05/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Relativistic shocks can accelerate particles by the first-order Fermi mechanism; the particles then emit synchrotron emission in the post-shock gas. This process is of particular interest in the models used for the afterglow of gamma-ray bursts. In this paper we use recent results in the theory of particle acceleration at highly relativistic shocks to model the synchrotron emission in an evolving, inhomogeneous and highly relativistic flow. We have developed a numerical code that integrates the relativistic Euler equations for fluid dynamics with a general equation of state, together with a simple transport equation for the accelerated particles. We present tests of this code and, in addition, we use it to study the gamma-ray burst afterglow predicted by the fireball model, along with the hydrodynamics of a spherically-symmetric relativistic blast wave. We find that, while broadly speaking the behaviour of the emission is similar to that already predicted with semi-analytic approaches, the detailed behaviour is somewhat different. The ‘breaks’ in the synchrotron spectrum behave differently with time, and the spectrum above the final break is harder than had previously been expected. These effects are due to the incorporation of the geometry of the (spherical) blast wave, along with relativistic beaming and adiabatic cooling of the energetic particles leading to a mix, in the observed spectrum, between recently injected ‘uncooled’ particles and the older ‘cooled’ population in different parts of the evolving, inhomogeneous flow.