Evolution of black hole mass and spin in collapsars

Abstract

We investigate the collapsar scenario, in which, according to Woosley (1993) and Paczynski (1998), the long gamma ray bursts (LGRBs) can be explained. The total energetics of explosions observed in the gamma ray band are consistent here with the total binding energy of a pogenitor star. However, the details characteristic for various events, such as their individual duration times, lightcurve profiles, variability, and connection with supernovae of different spectral properties, are still subject of many studies. In our scenario, the evolved progenitor star is collapsing onto a compact core, which forms a spinning black hole. The process of accretion via rotationally supported torus powers the ejection of relativistic jets. Here, the rotational energy of the black hole is presumably transported to the remote jet, which is mediated by magnetic fields. The rotation of pre-supernova star is a key property of the model. In our study, we investigate different types of collapsing stars: magnetized and non-magnetized. We probe the distributions of angular momentum inside the collapsar and the process of spinning up the black hole. Both Kerr parameter, and increasing mass of the black hole, put a constraint for the existence of rotationally supported torus inside the collapsar's envelope.