Swift J1644+57: An Ultra-Luminous X-ray Event

TL;DR

This paper proposes that the transient event Sw J1644+57 is an Ultra-Luminous X-ray event (ULX-E), caused by a star being tidally disrupted by a supermassive black hole, exhibiting super-Eddington accretion and luminosity.

Contribution

It introduces the ULX-E model for Sw J1644+57, linking its properties to ULXs and suggesting observational tests for this new classification.

Findings

Sw J1644+57's spectral energy distribution resembles ULXs.

The transient is likely due to a tidal disruption event.

The accretion flow maintains high radiative efficiency at super-Eddington rates.

Abstract

The photon spectral energy distribution of the powerful transient Sw J1644+57 resembles those of the brightest Ultra-Luminous X-ray sources (ULXs). The transient nature of Sw J1644+57 is likely the result of a tidal disruption of a star by a super-massive black hole. The stellar disk generates accretion power at super-Eddington rates and the observational properties of Sw J1644+57 indicate -- in analogy with ULXs -- that the accretion flow maintains a high level of radiative efficiency with a corresponding super-Eddington luminosity. Due to its similarity to ULXs, this powerful transient may be thought of as an Ultra-Luminous X-ray event (ULX-E). Observational tests for this ULX-E model are proposed as well.