4 Dissipative Photosphere Models of Gamma - ray Bursts and X - ray Flashes

We consider dissipative effects occurring in the optically thick inner parts of the rela-tivistic outflows producing gamma-ray bursts and X-ray flashes, emphasizing specially the Comptonization of the thermal radiation flux that is advected from the base of the outflow. Such dissipative effects –e.g. from magnetic reconnection, neutron decay or shocks – would boost the energy density of the thermal radiation. The dissipation probably leads to pair production; the pairs create an effective photosphere further out than the usual baryonic one. We suggest that the spectral peak in gamma ray bursts is essentially due to the Comp-tonized thermal component from the photosphere where the optical depth in the outflow falls to unity. Typical peak photon energies range between those of classical bursts and X-ray flashes. The relationship between the observed photon peak energy and the luminosity depends on the details of the dissipation, but under plausible assumptions can resemble the observed correlations.