Particle acceleration at relativistic shocks

The process of Diffusive Shock Acceleration near (ultra-)relativistic shocks is considered. It is shown that relativistic kinematics limits the energy gain at the shock to Delta epsilon similar to epsilon per crossing cycle. Like its non-relativistic counterpart, the mechanism is robust in the sense that it produces a power-law spectrum of accelerated particles with a slope s = -d ln N(epsilon)/d ln epsilon approximate to 2.2 - 2.3 under a wide number of circumstances.