The Definitive X-ray Light Curve of Swift J164449.3+573451

TL;DR

This paper presents the comprehensive X-ray light curve of Swift J164449.3+573451, a unique transient event likely caused by a relativistic jet from a tidal disruption of a star by a black hole, with detailed decay analysis and implications.

Contribution

It provides the definitive X-ray light curve of Swift J164449.3+573451 and interprets its decay and shutdown as evidence of jet activity related to tidal disruption events.

Findings

X-ray flux decayed as approximately t^{-1.5} over 17 months.

A rapid shutdown of the jet occurred within 24 hours.

The event is consistent with a tidal disruption of a star by a black hole.

Abstract

On March 28, 2011, the Swift Burst Alert Telescope triggered on an object that had no analog in over six years of Swift operations. Follow-up observations by the Swift X-ray Telescope (XRT) found a new, bright X-ray source covering 3 orders of magnitude in flux over the first few days, that was much more persistent (and variable) than gamma-ray burst afterglows. Ground-based spectroscopy found a redshift of 0.35, implying extremely high luminosity, with integrated isotropic-equivalent energy output in the X-ray band alone exceeding $10^{53}$ ergs in the first two weeks after discovery. Strong evidence for a collimated outflow or beamed emission was found. The observational properties of this object are unlike anything ever before observed. We interpret these unique properties as the result of emission from a relativistic jet produced in the aftermath of the tidal disruption of a main sequence star by a massive black hole (BH) in the center of the host galaxy. The source decayed slowly as the stellar remnants were accreted onto the BH, before abruptly shutting off. Here we present the definitive XRT team light curve for Swift J164449.3+573451 and discuss its implications. We show that the unabsorbed flux decayed roughly as a $t^{-1.5}$ power law up to August 17, 2012. The steep turnoff of an order of magnitude in 24 hours seems to be consistent with the shutdown of the jet as the accretion disk transitioned from a thick disk to a thin disk. Swift continues to monitor this source in case the jet reactivates.