Exceptional AGN long-timescale X-ray variability: The case of PHL 1092

¹ Centro de Astrobiología (CSIC–INTA), Dep. de Astrofísica; ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid
² Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab., Univeristy Park, PA 16802, USA
³ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
⁴ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
⁵ Department of Astronomy & Physics, Saint Mary’s University, 923 Robie Street, Halifax, NS B3H 3C3, UK
⁶ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

^a e-mail: gminiutti@cab.inta-csic.es

Abstract

PHL 1092 is a z ∼ 0.4 high-luminosity counterpart of the class of Narrow–Line Seyfert 1 galaxies. In 2008, PHL 1092 was found to be in a remarkably low X-ray flux state during an XMM–Newton observation. Its 2 keV flux density had dropped by a factor of ∼ 260 with respect to a previous observation performed 4.5 yr earlier. The UV flux remained almost constant, resulting in a significant steepening of the optical-to-X-ray slope α_ox from − 1.57 to − 2.51, making PHL 1092 one of the most extreme X-ray weak quasars with no observed broad absorption lines (BALs) in the UV. We have monitored the source since 2008 with three further XMM–Newton observations, producing a simultaneous UV and X-ray database spanning almost 10 yr in total in the activity of the source. We present here results from our monitoring campaign.