Dissipative Photosphere Models of Gamma‐Ray Bursts and X‐Ray Flashes

We consider dissipative effects occurring in the optically thick inner partsof the relativistic outflows producing gamma-ray bursts and X-ray flashes,emphasizing specially the Comptonization of the thermal radiation flux that isadvected from the base of the outflow. Such dissipative effects --e.g. frommagnetic reconnection, neutron decay or shocks -- would boost the energydensity of the thermal radiation. The dissipation can lead to pair production,in which case the pairs create an effective photosphere further out than theusual baryonic one. In a slow dissipation scenario, pair creation can besuppressed, and the effects are most important when dissipation occurs belowthe baryonic photosphere. In both cases an increased photospheric luminosity isobtained. We suggest that the spectral peak in gamma ray bursts is essentiallydue to the Comptonized thermal component from the photosphere, where thecomoving optical depth in the outflow falls to unity. Typical peak photonenergies range between those of classical bursts and X-ray flashes. Therelationship between the observed photon peak energy and the luminosity dependson the details of the dissipation, but under plausible assumptions can resemblethe observed correlations.Comment: Ap.J. in press, 14 pages, AAS latex, 3 figure