Quasi–thermal comptonization and GRBs

Quasi–thermal Comptonization in internal shocks formed between relativistic shells can account for the high energy emission of gamma–ray bursts (GRB). This is the dominant cooling mechanism if the typical energy of the emitting particles is achieved either through the balance between heating and cooling or as a result of electron–positron (e) pair production. Both processes yield sub/mildly relativistic energies. In this case the synchrotron spectrum is self–absorbed, providing the seed photons for the Comptonization process, whose spectrum is flat [ const] , ending either in an exponential cutoff or a Wien peak.