A tidal disruption-like X-ray flare from the quiescent galaxy SDSS J120136.02+300305.5⋆
1 XMM SOC, ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain
2 Dept. of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
3 Technische Universität München, Fakultät für Physik, James-Franck-Strasse 1/I, 85748 Garching, Germany
4 Excellence Cluster Universe, TUM, Boltzmannstrasse 2, 85748 Garching, Germany
5 Max Planck Institut für Plasmaphysik, Boltzmannstrasse 2, 85748 Garching, Germany
6 National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, 100012 Beijing, PR China
7 National Research Council, Herzberg Institute of Astrophysics, DRAO, Box 248, Penticton BC, V2A 6J9, Canada
8 Dept of Physics and Astronomy, University of Calgary, 2500 University Dr. NW., Calgary, AB T2N 1N4, Canada
9 Centro de Astrobiología Depto. Astrofisica (INTA-CSIC), ESAC campus, Apartado 78, 28691 Villanueva de la Cañada, Spain
10 Calar Alto Observatory, Centro Astronómico Hispano Alemán, Almería, Spain
Received: 31 October 2011
Accepted: 25 February 2012
Aims. The study of tidal disruption flares from galactic nuclei has historically been hampered by a lack of high quality spectral observations taken around the peak of the outburst. Here we introduce the first results from a program designed to identify tidal disruption events at their peak by making near-real-time comparisons of the flux seen in XMM-Newton slew sources with that seen in ROSAT.
Methods. Flaring extragalactic sources, which do not appear to be AGN, are monitored with Swift and XMM-Newton to track their temporal and spectral evolution. Timely optical observations are made to monitor the reaction of circumnuclear material to the X-ray flare.
Results. SDSS J120136.02+300305.5 was detected in an XMM-Newton slew from June 2010 with a flux 56 times higher than an upper limit from ROSAT, corresponding to LX ~ 3 × 1044 erg s-1. It has the optical spectrum of a quiescent galaxy (z = 0.146). Overall the X-ray flux has evolved consistently with the canonical t−5/3 model, expected for returning stellar debris, fading by a factor ~300 over 300 days. In detail the source is very variable and became invisible to Swift between 27 and 48 days after discovery, perhaps due to self-absorption. The X-ray spectrum is soft but is not the expected tail of optically thick thermal emission. It may be fit with a Bremsstrahlung or double-power-law model and is seen to soften with time and declining flux. Optical spectra taken 12 days and 11 months after discovery indicate a deficit of material in the broad line and coronal line regions of this galaxy, while a deep radio non-detection implies that a jet was not launched during this event.
Key words: X-rays: galaxies / galaxies: individual: SDSS J120136.02+300305.5
Partly based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC) and observations made with the WHT operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
© ESO, 2012