GRB/HN from Kerr Black Holes in Binaries

The Collapsar model, in which a massive star (greater than 20 solar masses) fails to produce a SN and forms a BH, provides the main framework for understanding long Gamma-Ray Bursts (GRB) and the accompanying hypernovae (HN). However, single massive-star models that explain the population of pulsars, predict cores that rotate too slowly to produce GRBs/HNe. We present a model of binary evolution that allows the formation of Kerr black holes (BH) where the spin of the BH can be estimated from the pre-collapse orbit, and use the Blandford-Znajek (BZ) mechanism to estimate the available energy for a GRB/HN. A population synthesis study shows that this model can account for both, the long GRB and the subluminous GRB populations.