The Close AGN Reference Survey (CARS)

What is causing Mrk 1018’s return to the shadows after 30 years?^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
e-mail: bhuseman@eso.org
² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³ Yale Center for Astronomy and Astrophysics, Yale University, 52 Hillhouse Ave., New Haven, CT 06511, USA
⁴ Max-Planck-Institut für extraterrestische Physik, Giessenbachstr. 1, 85748 Garching, Germany
⁵ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
⁶ LERMA, Observatoire de Paris, College de France, PSL, CNRS, Sorbonne Univ., UPMC, 75014 Paris, France
⁷ Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia
⁸ ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia
⁹ School of Physics & Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, UK
¹⁰ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹¹ Instituto de Astrofísica de Andalucía, Glorieta de las Astronomía s/n, 18008 Granada, Spain
¹² Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Pl., Hilo, Hawaii, 96720, USA

Received: 4 July 2016
Accepted: 16 August 2016

Abstract

We recently discovered that the active galactic nucleus (AGN) of Mrk 1018 has changed optical type again after 30 yr as a type 1 AGN. Here we combine Chandra, NuStar, Swift, Hubble Space Telescope and ground-based observations to explore the cause of this change. The 2–10 keV flux declines by a factor of ~8 between 2010 and 2016. We show with our X-ray observation that this is not caused by varying neutral hydrogen absorption along the line-of-sight up to the Compton-thick level. The optical-UV spectral energy distributions are well fit with a standard geometrically thin optically thick accretion disc model that seems to obey the expected L ~ T⁴ relation. It confirms that a decline in accretion disc luminosity is the primary origin for the type change. We detect a new narrow-line absorber in Lyα blue-shifted by ~700 km s^-1 with respect to the systemic velocity of the galaxy. This new Lyα absorber could be evidence for the onset of an outflow or a companion black hole with associated gas that could be related to the accretion rate change. However, the low column density of the absorber means that it is not the direct cause for Mrk 1018’s changing-look nature.