Gamma-Ray Bursts from Stellar Collapse to a Black Hole?

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Session 55 -- SN 1993J; High Energy Astrophysics
Oral presentation, Wednesday, 10:30-12:00, Dwinelle 145 Room

[55.05] Gamma-Ray Bursts from Stellar Collapse to a Black Hole?

S. E. Woosley (UCO/Lick Obs., Astronomy Board, UCSC)

The mystery of the origin of gamma-ray bursts seems deeper with each passing year, but observational evidence has become compelling that sources at cosmological distances may be required and that these sources are characterized by relativistic collimated motion, i.e., jets. In many cases the evolution of a massive star may end not in the production of a supernova but a black hole. Such occurrences should be common in stars of exceptionally high mass (helium cores bigger than 10 solar masses) and low metallicity and may also occur in stars that have lost their hydrogen envelopes. Any reasonable assumption regarding angular momentum then leads to a massive accretion disk that flows, on a viscous time scale, into a black hole that very rapidly approaches the Kerr limit. The dissipation of 10$^{54}$ erg of rotational and gravitational energy within the geometry of a thick torus is very likely to lead to jets, possibly by the Blandford-Znajek mechanism (MNRAS, 179, 433, 1977) or whatever functions to power active galactic nuclei. The total energy requirement for the burst is about 10$^{49}$ erg, or less than 0.01\% of the total energy dissipation, most of which goes into neutrinos and mass motion. The emission produced by the jet will be beamed and the number of actual GRB's as great as 10$^6$ per year, possible in a stellar collapse model but not by merging neutron stars. Part of the temporal structure of the event could be due to the passage of the beam across the earth, as in pulsars. The greatest challenge to this sort of model is producing a relatively clean jet only mildly contaminated by baryonic matter.

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