An X-ray and UV flare from the galaxy XMMSL1 J061927.1-655311

¹ XMM SOC, ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain
e-mail: richard.saxton@sciops.esa.int
² Dept. of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
³ Max-Planck Institut für Radioastronomie, Auf dem Huegel 69, 53121 Bonn, Germany
⁴ Centro de Astrobiología Depto. Astrofisica (INTA-CSIC), ESAC campus, Apartado 78, 28691 Villanueva de la Cañada, Spain
⁵ School of Physical Sciences, University of Tasmania, 7001 Hobart TAS, Australia
⁶ Departamento de Astrofsica, Facultad de CC. Fsicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁷ Research School of Astronomy and Astrophysics, Australian National University, 2611 Canberra, ACT, Australia
⁸ CSIRO Astronomy and Space Science, PO Box 76, Epping NSW 1710, Australia

Received: 5 June 2014
Accepted: 22 September 2014

Abstract

Aims. New high variability extragalactic sources may be identified by comparing the flux of sources seen in the XMM-Newton Slew Survey with detections and upper limits from the ROSAT All Sky Survey.

Methods. A detected flaring extragalactic source was monitored with Swift and XMM-Newton to track its temporal and spectral evolution. Optical and radio observations were made to help classify the galaxy, investigate the reaction of circumnuclear material to the X-ray flare, and check for the presence of a jet.

Results. In November 2012, X-ray emission was detected from the galaxy XMMSL1 J061927.1-655311 (a.k.a. 2MASX 06192755-6553079), a factor 140 times higher than an upper limit from 20 years earlier. Both the X-ray and UV flux subsequently fell over the following year by factors of 20 and 4, respectively. Optically, the galaxy appears to be a Seyfert I with broad Balmer lines and weak, narrow, low-ionisation emission lines, at a redshift of 0.0729. The X-ray luminosity peaks at L_X ~ 8 × 10⁴³ erg s^-1 with a typical Sy I-like power-law X-ray spectrum of Γ ~ 2. The flare has either been caused by a tidal disruption event or by an increase in the accretion rate of a persistent active galactic nucleus.