Evolution of tidal disruption candidates discovered by XMM-Newton

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany e-mail: pili@mpe.mpg.de
² Dept. of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
³ ESA/ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, España
⁴ Instituto de Astrofísica de Canarias, La Laguna 38200, Tenerife, Spain
⁵ Center for Astrophysics, University of Science and Technology of China, Hefei, Anhui, 230026, PR China
⁶ Dept. of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK

Received: 1 May 2008
Accepted: 22 July 2008

Abstract

Context. It has been demonstrated that active galactic nuclei are powered by gas accretion onto supermassive black holes located at their centres. The paradigm that the nuclei of inactive galaxies are also occupied by black holes was predicted long ago by theory. In the past decade, this conjecture was confirmed by the discovery of giant-amplitude, non-recurrent X-ray flares from such inactive galaxies and explained in terms of outburst radiation from stars tidally disrupted by a dormant supermassive black hole at the nuclei of those galaxies.

Aims. Due to the scarcity of detected tidal disruption events, the confirmation and follow-up of each new candidate is needed to strengthen the theory through observational data, as well as to shed new light on the characteristics of this type of events.

Methods. Two tidal disruption candidates have been detected with XMM-Newton during slew observations. Optical and X-ray follow-up, post-outburst observations were performed on these highly variable objects in order to further study their classification and temporal evolution.

Results. We show that the detected low-state X-ray emission for these two candidates has properties such that it must still be related to the flare. The X-ray luminosity of the objects decreases according to theoretical predictions for tidal disruption events. At present, optical spectra of the sources do not present any evident signature of the disruption event. In addition, the tidal disruption rate as derived from the XMM-Newton slew survey has been computed and agrees with previous studies.