PARTICLE ACCELERATION AT RELATIVISTIC SHOCKS AND CURRENT SHEETS

Simple kinematic theories of particle acceleration at relativistic shocks lead to the prediction of a highenergy spectral index of 1.1 for the energy ux of synchrotron photons. However, several effects can change this picture. In this paper I discuss this theory briey and mention recent developments concerning shock formation and magnetic eld generation. An additional mechanism must operate at lower energy and current sheets present a possible alternative acceleration site; I summarize some recent work on the relativistic version of these objects.