Letter to the Editor

A candidate tidal disruption event in the Galaxy cluster Abell 3571

¹ Max-Planck-Institute für Extraterrestrische Physik, Postfach 1312, 85741, Garching bei München, Germany e-mail: cap@mpe.mpg.de
² University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
³ SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
⁴ KIPAC, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
⁵ Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA 02139, USA
⁶ California Institute of Technology, 105-24 Robinson, 1200 East California Boulevard, Pasadena, CA 91125, USA
⁷ Dept. of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
⁹ Department of Astronomy and Astrophysics, Pontificia Universidad Catolica de Chile. Casilla 306, Santiago 22, Santiago, Chile

Received: 5 December 2008
Accepted: 18 January 2009

Abstract

Context. Tidal disruption events are possible sources of temporary nuclear activity in galactic nuclei and can be considered as good indicators of the existence of supermassive black holes in the centers of galaxies.

Aims. A new X-ray source has been detected serendipitously with ROSAT in a PSPC pointed observation of the galaxy cluster A3571. Given the strong flux decay of the object in subsequent detections, the tidal disruption scenario is investigated as a possible explanation of the event.

Methods. We followed the evolution of the X-ray transient with ROSAT, XMM-Newton and Chandra for a total period of ~13 years. We also obtained 7-band optical/NIR photometry with GROND at the ESO/MPI 2.2 m telescope.

Results. We report a very large decay of the X-ray flux of the ROSAT source identified with the galaxy LEDA 095953, a member of the cluster Abell 3571. We measured a maximum 0.3-2.4 keV luminosity Log (L_X) = 42.8 erg s^-1. The high state of the source lasted at least 150 ks; afterwards L_X declined as ~t^-2. The spectrum of the brightest epoch is consistent with a black body with temperature 0.12 keV.

Conclusions. The total energy released by this event in 10 yr was estimated to be  > 2  10⁵⁰ erg. We interpret this event as a tidal disruption of a solar type star by the central supermassive black hole (i.e. ~10) of the galaxy.