E. Quasi-Thermal Comptonization

Ghisellini and Celotti [124] suggested that the prompt GRB emission arises in a quasi-thermal Comptonization process. In their model the optical depth within the emitting region (of internal shocks) is of order unity leading to a copious pair production. The system is optically thick to synchrotron emission. The self-absorbed synchrotron emission is the seed for an Inverse Compton emission produced by the pairs. The effective Compton paramter in the new system, , is:

(38)

where T' is the effective temperature of the pair and is the total cross section for scattering. The pairs act as a thermostat controlling the effective temperature within the emitting region to 30-300 kev [399, 400]. The resulting spectrum from this model is a flat spectrum F ⁰ between the h_sa and kT' [124]. The spectrum will evolve rapidly during the burst while the pairs are being created and the effective temperature decreases.