An X-ray Survey for Tidal Disruption Flares in Rich Clusters of Galaxies

We present the results of an archival survey to search for tidal disruption flares and thereby constrain the rate at which they occur. Tidal disruption flares are extremely rare, and new examples are needed to constrain the physics of their phenomenology, as well as models of galactic formation and evolution. By examining X-ray observations of 10 galaxy clusters which have been observed multiple times via Chandra and XMM-Newton over the course of 13 years, we have identified two luminous, supersoft X-ray flares in the direction of Abell 1689 and Abell 1795. We argue that these flares are best described as arising from the disruption and subsequent accretion of stellar material by massive black holes in the centers of galaxies in those clusters. These flares represent 10% of all known tidal flare candidates. Among the tidal flare candidates presented to date, the flare in Abell 1795 has some of the best X-ray photon statistics and one of the best-sampled light curves. The Abell 1795 flare may indicate a central black hole that is an order of magnitude more massive than would be expected for its host galaxy, WINGS J134849.88+263557.5 (WINGS J1348). WINGS J1348 may also be the least massive galaxy to host a massive central black hole. One possible explanation for this unusual scenario is a past encounter with another galaxy that stripped some fraction of the stellar matter of WINGS J1348. Extreme ultraviolet data associated with the flare may make the WINGS J1348 flare the only known tidal flare to have been observed in the extreme ultraviolet near its peak. We also calculate the rate of tidal disruption from detailed analysis of Abell 1689. We present a preliminary revision of this rate based on the full dataset of 2 tidal flares and 10 clusters. In addition, we review the numerous paradigm-changing theoretical and observational developments in the study of tidal flares from recent years, and for the first time compare black hole masses as derived from various tidal flare signatures to black hole masses expected from host galaxy bulge luminosities.