Discovery of a tidal disruption event candidate from the 2XMM catalog
1 CNRS, IRAP, 9 avenue du Colonel Roche, BP. 44346 31028 Toulouse Cedex 4, France
2 Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
3 Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA
4 Gemini Observatory/AURA, Southern Operations Center, Casilla 603, La Serena, Chile
5 Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
6 Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, NSW 2006, Australia
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Stars approaching a supermassive black hole (SMBH) can be tidally disrupted and subsequently accreted, providing a unique way to find and study inactive SMBHs. We report on our discovery of a new tidal disruption event candidate, 2XMMi J184725.1-631724, with unprecedented ultrasoft X-ray spectra near the flare peak. It lies toward the center of an inactive galaxy at z = 0.0353. It was detected serendipitously in two XMM-Newton observations separated by 211 days, with the flux increasing by a factor of ∼9. The source was not detected in X-rays by ROSAT in 1992, indicating a long-term variability factor of >64; neither by Swift in 2011, implying a flux decay factor of >12 since the last XMM-Newton observation. The XMM-Newton X-ray spectra are dominated by a strong cool thermal disk (>80%, tens of eV) with the luminosity appearing to follow the L ∝ T4 relation, often seen in the thermal state of the BH X-ray binaries. Both XMM-Newton observations show large variability on timescales of hours. This can be explained as due to fast variations in the mass accretion rate, maybe caused by the shocks during the tidal disruption of the star.
© Owned by the authors, published by EDP Sciences, 2012
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