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Astron. Astrophys. Suppl. Ser. 138, 499-502

Central engines for gamma-ray bursts

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 $\Gamma$ 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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