General Relativistic MHD Simulations of the Gravitational Collapse of a Rotating Star with Magnetic Field as a Model of Gamma-Ray Bursts

We have performed 2.5-dimensional general relativistic MHD simulations of the gravitational collapse of a rotating massive star with magnetic field as a model of gamma ray bursts (GRBs). This simulation showed the generation of jet-like-outflow from the gravitational collapse. We found the jet is accelerated by the gradient force of gas pressure and the centrifugal force and is collimated by the pinching force of toroidal magnetic field and the effect of geometry of magnetic field.