Black hole Spin in Sw J1644+57 and Sw J2058+05

TL;DR

This paper investigates the black hole spins in two relativistic jet events, Sw J1644+57 and Sw J2058+05, suggesting high spins are crucial for jet launching via the Blandford-Znajek mechanism.

Contribution

It constrains the black hole spin parameters in these events, linking high spin to the occurrence of relativistic jets in tidal disruption events.

Findings

Both black holes have moderate to high spins.

High black hole spin likely facilitates jet launching.

Relativistic jets are rare, possibly due to high spin requirement.

Abstract

Recently a hard X-ray transient event, Sw J1644+57, was discovered by the Swift satellite. It likely marks the onset of a relativistic jet from a supermassive black hole, possibly triggered by a tidal disruption event. Another candidate in the same category, Sw J2058+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 black holes. We attribute jet launching to the Blandford-Znajek mechanism, and use the available data to constrain the black hole spin parameter for the two events. It is found that the two black holes indeed carry a moderate to high spin, suggesting that black hole spin is likely the crucial factor behind the Sw J1644+57 - like events.