Hyper-accreting tori of Gamma Ray Bursters

Abstract

We present numerical simulations of axisymmetric magnetised massive tori around rotating black holes taking into account the energy losses due to emission of neutrinos. A realistic equation of state is used which takes into account the energy losses due to dissociation of nuclei. The heating due to neutrino-antineutrino annihilation is not included. We study the cases of optically thick, semi-transparent, and optically thin to neutrino discs. We show that neutrino cooling does not change significantly the structure of accretion flow and the total energy release. The time scale of accretion is set by the torus angular momentum. Due to the lack of magnetic dynamo in our calculations, it is the initial strength of magnetic field and its topology that determine the process of jet formation and its energetics. Extrapolation of our results gives the total energy released in the jet $\sim 10^{52}$ erg. This is sufficient to explain the hypernovae explosions associated with GRB 980425 and GRB 030329.