Astron. Astrophys. Suppl. Ser. 138, 527-528

Quasi-thermal comptonization and GRBs

G. Ghisellini¹ and A. Celotti²

1 - Osservatorio Astronomico di Brera, via Bianchi 46, I-23807 Merate, Italy
e-mail: gabriele@merate.mi.astro.it
2 - S.I.S.S.A., via Beirut 2-4, I-34014, Italy
e-mail: celotti@sissa.it

Received December 18, 1998; accepted January 26, 1999

Abstract:

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$^{\pm}$) 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 [$F(\nu)\sim$const], ending either in an exponential cutoff or a Wien peak.

Key words: gamma rays: bursts -- radiation mechanisms: non-thermal, thermal -- X-rays: general