The MHD collapsar model for GRBs: an inflow produces an outflow
  We present our recent results from numerical simulations of a magnetized flow in the vicinity of a black hole in the context of the collapsar model for GRBs. The simulations show that after an initial transient, the flow settles into a complex convolution of several distinct, time-dependent flow components including an accretion torus, its corona and outflow, an inflow and an outflow in the polar funnel. We focus on studying the nature and connection between these components, in particular between the inflows and related outflows. We find that rotational and MHD effects launch, accelerate, and sustain the outflows. We also find that an outflow can be formed even when the collapsing envelope has initially a very weak magnetic field and a very small angular momentum. Our main conclusion is that even for a relatively weak initial magnetic field and a slow rotation, a gravitational collapse of a stellar envelope can lead to formation of a very strong and very fast jet. 
Daniel Proga (UNLV)