Heidelberg Joint Astronomical Colloquium

Relativistic bulk motion is known to occur in several astrophysical objects. These flows are generally identified via their non-thermal radiation spectra and are often associated with the presence of shocks. One possible source of this radiation is the synchrotron and inverse-Compton radiation produced by a population of shock accelerated electrons. The theory of Fermi acceleration at relativistic shocks is reviewed, and shown to be generally consistent with the observed power-law index of the non-thermal emission spectra. In light of recent simulations, the maximum energy photon energies that can be produced via synchrotron-type processes is revisited. This places stringent limits on synchrotron models of recent FERMI observations of GeV emission from GRBs.