GAMMA-RAY BURSTS FROM STELLAR MASS ACCRETION DISKS AROUND BLACK-HOLES

A cosmological model for gamma-ray bursts is explored in which the radiation is produced as a broadly beamed pair fireball along the rotation axis of an accreting black hole. The black hole may be a consequence of neutron star merger or neutron star-black hole merger, but for long complex bursts, it is more likely to come from the collapse of a single Wolf-Rayet star endowed with rotation (''failed'' Type Ib supernova). The disk is geometrically thick and typically has a mass inside 100 km of several tenths of a solar mass. In the failed supernova case, the disk is fed for a longer period of time by the collapsing star. At its inner edge the disk is thick to its own neutrino emission and evolves on an viscous time scale of several seconds. In a region roughly 30 km across, interior to the accretion disk and along its axis of rotation, a pair fireball is generated by neutrino annihilation and electron-neutrino scattering which deposit approximately 10(50) ergs s-1. Electron scattering is more important in those cases where the baryonic contamination is high and the time scale for expansion increased. Extensive baryonic mass loss also occurs from the disk, and this may pose problems for production of a hard burst. Gamma-ray burst or not, this sort of event should occur in nature and should have an observable counterpart.