Hyper- and suspended-accretion states of rotating black holes and the durations of gamma-ray bursts

We analyze the temporal evolution of accretion onto rotating black holes subject to large-scale magnetic torques. Wind torques alone drive a disk toward collapse in a finite time similar to E-ff(k)/E-B, where t(ff) is the initial free-fall time and E-k/E-B is the ratio of kinetic energy to poloidal magnetic energy. Additional spin-up torques from a rapidly rotating black hole can arrest the disk's inflow. We associate short/long gamma-ray bursts with hyperaccretion/suspended-accretion onto slowly/rapidly spinning black holes. This model predicts afterglow emission from short bursts and may be tested by HETE-2.