Open AccessRelativistic blast waves and synchrotron emission
Author(s) -
Downes T. P.,
Duffy P.,
Komissarov S. S.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05282.x
Subject(s) - physics , blast wave , relativistic speed , fermi acceleration , shock wave , synchrotron , equation of state , relativistic particle , fermi gamma ray space telescope , afterglow , gamma ray burst , particle acceleration , astrophysics , relativistic beaming , shock (circulatory) , acceleration , astrophysical jet , synchrotron radiation , classical mechanics , mechanics , active galactic nucleus , nuclear physics , quantum mechanics , galaxy , electron , medicine
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.