Astron. Astrophys. Suppl. Ser. 138, 499-502
S.E. Woosley and A.I. MacFadyen
Send offprint request: S.E. Woosley
Astronomy Department, UCSC, Santa Cruz, CA 95064, U.S.A.
Received December 29, 1998; accepted March 10, 1999
What powers a gamma-ray burst (GRB)? We discuss here some properties of several currently favored models based on black hole accretion with emphasis on the collapsar - a rotating massive star whose iron core collapse produces a black hole. Depending on mass, rotation rate, and viewing angle, collapsars can explain a wide gambit of GRBs from faint events like GRB 980425, to bright ones like GRB 971214. Because of accretion disk instabilities, the in the jet may be rapidly time variable. The burst itself is made by a combination of internal shocks in the jet and external shocks with the pre-explosive stellar wind. Beaming for hard gamma-rays is about 1%, but mildly relativistic matter is ejected at larger angles. All collapsars produce Type Ib/c supernovae like SN 1998bw, but the converse is not true. Most Type Ib/c supernovae do not make GRBs.
Key words: black holes -- accretion; gamma-ray bursts
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