title: Magnetohydrodynamic simulations of the collapsar model for early and late evolution of gamma-ray bursts.
abstract: I present results from magnetohydrodynamic (MHD) simulations of a gaseous envelope collapsing onto a black hole (BH). These results support the notion that the collapsar model is one of the most promising scenarios to explain the huge release of energy in a matter of seconds associated with gamma-ray bursts (GRBs). Additionally, the MHD simulations show that at late times, when the mass supply rate is expected to decrease, the region in the vicinity of the BH can play an important role in determining the rate of accretion, its time behaviour and ultimately the energy output. In particular, the magnetic flux accumulated around the BH can repeatedly stop and then restart the energy release. As proposed by Proga & Zhang, the episode or episodes of reoccurrence of accretion processes can correspond to X-ray flares discovered recently in a number of GRBs.
authors.affiliation: Physics Department, University of Nevada, Las Vegas, NV 89154, USA. dproga@physics.unlv.edu
authors.forename: Daniel
authors.initials: D
authors.lastname: Proga