Gamma Ray Burst Production and Supernova Signatures in Slowly Rotating Collapsars

We consider accretion onto newborn black holes following the collapse of rotating massive stellar cores, at the threshold where a centrifugally supported disk gives way to nearly radial inflow for low angular momentum. For realistic initial conditions taken from pre-supernova (pre-SN) evolution calculations, the densities and temperatures involved require the use of a detailed equation of state and neutrino cooling processes, as well as a qualitative consideration of the effects of general relativity. Through two-dimensional dynamical calculations we show how the energy release is affected by the rotation rate and the strength of angular momentum transport, giving rise to qualitatively different solutions in limits of high and low angular momentum, each being capable of powering a gamma-ray burst (GRB). We explore the likelihood of producing Fe-group elements in the two regimes and suggest that while large and massive centrifugally supported disks are capable of driving strong outflows with a possible SN-like signature, quasi-radial flows lack such a feature and may produce a GRB without such an accompanying feature, as seen in GRB060505.