Ultraviolet Detection of the Tidal Disruption of a Star by a Supermassive Black Hole

A supermassive black hole in the nucleus of a galaxy will be revealed when astar passes close enough to be torn apart by tidal forces and a flare ofradiation is emitted by the stream of stellar debris that plunges into theblack hole. Since common active galactic nuclei have accreting black holes thatcan also produce flares, a convincing demonstration that a stellar tidaldisruption has occurred generally begins with a ``normal'' galaxy that has noevidence of prior nuclear activity. Here we report a luminous UV flare from anelliptical galaxy at z = 0.37 in the Groth field of the GALEX Deep ImagingSurvey that has no evidence of a Seyfert nucleus from optical spectroscopy andX-ray imaging obtained during the flare. Multiwavelength data collected at thetime of the event, and for 2 years following, allow us to constrain, for thefirst time, the spectral energy distribution of a candidate tidal disruptionflare from optical through X-rays. The luminosity and temperature of theradiation and the decay curve of the flare are in excellent agreement withtheoretical predictions for the tidal disruption of a star, and provide thestrongest empirical evidence for a stellar disruption event to date.Comment: To appear in Dec. 10, 2006 issue of ApJ Letter