A Tidal Disruption Flare in Abell 1689 from an Archival X-ray Survey of Galaxy Clusters

Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated stellar debris falls back onto the black hole itself. We examine the first results of an ongoing archival survey of galaxy clusters using Chandra and XMM-selected data, and report a likely tidal disruption flare from SDSS J131122.15-012345.6 in Abell 1689. The flare is observed to vary by a factor of >30 over at least 2 years, to have maximum L_X(0.3-3.0 keV)> 5 x 10^{42} erg s^{-1} and to emit as a blackbody with kT~0.12 keV. From the galaxy population as determined by existing studies of the cluster, we estimate a tidal disruption rate of 1.2 x 10^{-4} galaxy^{-1} year^{-1} if we assume a contribution to the observable rate from galaxies whose range of luminosities corresponds to a central black hole mass (M_bh) between 10^6 and 10^8 M_sun.Comment: 24 pages, including 6 figures and 2 tables Accepted for publication in the Astrophysical Journa

Spectral Models for Low-luminosity Active Galactic Nuclei in LINERs: The Role of Advection-dominated Accretion and Jets

We perform an exploratory study of the physical properties of accretion flows and jets in low-luminosity active galactic nuclei (LLAGNs) by modeling the spectral energy distributions (SEDs) of 12 LLAGNs in low-ionization nuclear emission-line regions (LINERs). These SEDs we constructed from high-resolution radio, X-ray and optical/UV observations of the immediate vicinity of the black hole. We adopt a coupled accretion-jet model comprising an inner advection-dominated accretion flow (ADAF) and an outer standard thin disk. We present best-fit models in which either the ADAF or the jet dominate the X-ray emission. Six sources in our sample display an optical-UV excess with respect to ADAF and jet models; this excess can be explained as emission from the truncated disk with transition radii 30-225 Rs in four of them. In almost all sources the optical emission can also be attributed to unresolved, old stellar clusters with masses ~1E7-1E8 Msun. We find evidence for a correlation between the accretion rate and jet power and an anti-correlation between the radio-loudness and the accretion rate. We confirm previous findings that the radio emission is severely underpredicted by ADAF models and explained by the relativistic jet. We find evidence for a nonlinear relation between the X-ray and bolometric luminosities and a slight IR excess in the average model SED compared to that of quasars. We suggest that the hardness of the X-ray spectrum can be used to identify the X-ray emission mechanism and discuss directions for progress in understanding the origin of the X-rays.Comment: Accepted for publication in MNRAS. 27 pages, 22 figures. arXiv admin note: substantial text overlap with arXiv:1112.464