Thermalization of the pair plasma and the consequences for Gamma-Ray Bursts

We consider initial conditions in the sources of Gamma-Ray Bursts. We show that hot and dense pair plasma, created in the source, relaxes to thermal equilibrium configuration with zero chemical potentials well before it starts to expand driven by the radiative pressure. The relaxation process follows the sequence: pairs, protons, photons, thus the first particles reaching the same temperature are electrons and positrons, while photons join the thermal math latest. We also show that light nuclear elements cannot be synthesized in the fireball.