The giant X-ray outbursts from nearby, non-active galaxies: tidal disruption flares ?

One efficient method to probe the direct vicinity of SMBHs in nearby galaxies is to make use of the detection of flares from tidally disrupted stars (e.g., Lidskii & Ozernoi 1979, Rees 1988). The first few excellent candidates for the occurrence of this process in non-active galaxies have emerged recently. Here, we present a review of these observations, compare with variability in AGN, and discuss theoretical implications. We concentrate on the cases of NGC 5905 and RXJ1242-1119, and report results from a systematic search for further X-ray flares from a sample of >100 nearby galaxies.Comment: 6 pages incl. 2 figures, needs agnsymp.cls; to appear in `ASCA/ROSAT Workshop on AGN and the X-ray Background' (Tokyo, Nov. 1-3, 1999), T. Takahashi and H. Inoue (eds). Typo in equation (1) corrected. Preprint and related papers also available at http://www.xray.mpe.mpg.de/~skomossa

X-rays from the environment of supermassive black holes in active galaxies

X-rays are a powerful probe of the physical conditions in the nuclei of active galaxies. We review the X-ray properties of radio-quiet AGN, LINERs and ultraluminous IR galaxies based on observations carried out with the X-ray satellite ROSAT. We then summarize the observations of giant X-ray flares from non-active galaxies, interpreted as stellar tidal disruptions by supermassive black holes.Comment: invited review, IX. Marcel Grossmann Meeting on General Relativity, Gravitation and Relativistic Field Theories (Rome, July 2000), session: `Astrophysics of Neutron Stars and Black Holes: Observations'; to appear in the online proceedings at http://www.icra.it/MG/mg9/mg9.htm, a 2-page condensate will be published in World Scientific; long and short version are also available at http://www.xray.mpe.mpg.de/~skomossa