Magnetic Fields, Accretion, and the Central Engine of Gamma-Ray Bursts

Abstract

I briefly review magnetic effects in accretion physics, and then go on to discuss a possible central engine for gamma-ray bursts. A rotating black hole immersed in a non-axisymmetric magnetic field experiences a torque trying to align spin and field. I suggest that gamma-ray burst hosts may provide conditions where this effect allows rapid extraction of a significant fraction of the hole's rotational energy. I argue that much of the electromagnetic emission is in two narrow beams parallel and antiparallel to the asymptotic field direction. This picture suggests that only a mass 10^-5 Msun is expelled in a relativistic outflow, as required by the fireball picture.

8 pages, Invited talk to appear in the Proceedings of Magnetic Fields in the Universe, Angra dos Reis, Brazil, November 28 - December 3 2004