Possible X-Ray Quasi-periodic Eruptions in a Tidal Disruption Event Candidate

Abstract

X-ray quasi-periodic eruptions (QPEs) are a recently discovered phenomenon associated with supermassive black holes at the centers of galaxies. They are high-amplitude soft X-ray flares that recur on timescales of hours, but what causes these flares remains uncertain. In the two years since their original discovery, four known QPE-hosting galaxies have been found, with varying properties and levels of activity. We have conducted a blind algorithm-assisted search of the XMM-Newton Source Catalog and found a fifth QPE candidate, XMMSL1 J024916.6-041244. This is a star-forming galaxy hosting a relatively low-mass nuclear black hole, and has previously been identified as a tidal disruption event candidate. An XMM-Newton pointed observation of the source in 2006 exhibited nearly two QPE-like flares in soft X-rays, and unlike in other QPE sources, there are hints of corresponding dips in the UV light curves. Afterwards, a series of Swift observations observed the rapid dimming of the source; thereafter, in 2021 August, we triggered a second XMM-Newton observation, which revealed that the source is detected, but the QPEs are no longer present. Here we report on (I) the strategy we used to systematically search through XMM-Newton archival data; (II) the properties of J0249 and its QPE flares; and (III) the relative behaviors and properties of the QPE sample to date, now five members large.