A Huge Drop in X-ray Luminosity of the Non-Active Galaxy RXJ1242.6-1119A, and First Post-Flare Spectrum - Testing the Tidal Disruption Scenario

It has been suggested that an unavoidable consequence of the existence of supermassive black holes, and the best diagnostic of their presence in non-active galaxies, would be occasional tidal disruption of stars captured by the black holes. These events manifest themselves in form of luminous flares powered by accretion of debris from the disrupted star into the black hole. Candidate events among optically non-active galaxies emerged in the past few years. For the first time, we have looked with high spatial and spectral resolution at one of these most extreme variability events ever recorded among galaxies. Here, we report measuring a factor ~200 drop in luminosity of the X-ray source RXJ 1242-1119 with the X-ray observatories Chandra and XMM-Newton, and perform key tests of the favored outburst scenario, tidal disruption of a star by a supermassive black hole. We show that the detected `low-state' emission has properties such that it must still be related to the flare. The power-law shaped post-flare X-ray spectrum indicates a `hardening' compared to outburst. The inferred black hole mass, the amount of liberated energy, and the duration of the event favor an accretion event of the form expected from the (partial or complete) tidal disruption of a star (abstract abbreviated).