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

摘要

We analyze the temporal evolution of accretion onto rotating black holessubject to large-scale magnetic torques. Wind torques alone drive a disktowards collapse in a finite time $\sim t_{ff} E_k/E_B$, where $t_{ff}$ is theinitial free-fall time and $E_k/E_B$ is the ratio of kinetic-to-poloidalmagnetic energy. Additional spin-up torques from a rapidly rotating black holecan arrest the disk's inflow. We associate short/long gamma-ray bursts withhyperaccretion/suspended-accretion onto slowly/rapidly spinning black holes.This model predicts afterglow emission from short bursts, and may be tested byHETE-II.