Energy and Radiation Spectrum of Electrons in Ultra-relativistic Shocks of GRB Afterglows

Abstract

We consider particle acceleration near ultra relativistic shocks (shock p 1) and the distribution of accelerated particles in the shock downstream. We suggest that the electron energy spectrum will settle mp into an "universal" power law with index p 2.2 above an "injection break" at e = i m shock, and e will be flatter at lower energies. The synchrotron radiation spectrum arising from these electrons is computed for a decelerating relativistic fireball. We show that this model can account well for the observed spectra and lightcurves of Gamma Ray Burst Afterglows.