Black hole spin in SwJ1644+57 and SwJ2058+05

Abstract

Recently, a hard X-ray transient event, SwJ1644+57, was discovered by the Swift satellite. It likely marks the onset of a relativistic jet from a supermassive black hole (BH), possibly triggered by a tidal disruption event (TDE). Another candidate in the same category, SwJ2058+05, was also reported. The low event rate suggests that only a small fraction of TDEs launch relativistic jets. A common speculation is that these rare events are related to rapidly spinning BHs. We attribute jet launching to the Blandford-Znajek mechanism and use the available data to constrain the BH spin parameter for the two events. It is found that the two BHs indeed carry a moderate to high spin, suggesting that BH spin is likely the crucial factor behind the SwJ1644+57-like events. © 2011. The American Astronomical Society. All rights reserved.