Direct probe of the inner accretion flow around the supermassive black hole in NGC 2617

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: m.giustini@sron.nl
² XMM-Newton Science Operations Centre, ESA/ESAC, Apartado 78, 28692 Villanueva de la Cañada, Madrid, Spain
³ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁴ Astronomical Institute, Academy of Sciences, Bocní II 1401, 14100 Prague, Czech Republic
⁵ University of Oxford, Department of Physics, Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁶ Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154, USA
⁷ ISDC, University of Geneva, Chemin d’Écogia 16, 1290 Versoix, Switzerland
⁸ Catedrática CONACYT – Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis E. Erro 1, Tonantzintla, Puebla, CP 72840, México
⁹ Centro de Astrobiología (CSIC-INTA), Dep. de Astrofísica; ESAC, PO Box 78, Villanueva de la Cañada, 28692 Madrid, Spain
¹⁰ Department of Earth and Space Science, Morehead State University, 235 Martindale Dr., Morehead, KY 40351, USA
¹¹ Astronomy Department, Ohio State University, Columbus, OH 43210, USA
¹² Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101, USA
¹³ Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejèrcito 441, Santiago, Chile
¹⁴ Millennium Institute of Astrophysics, Santiago, Chile

Received: 11 April 2016
Accepted: 31 July 2016

Abstract

Aims. NGC 2617 is a nearby (z ~ 0.01) active galaxy that recently switched from being a Seyfert 1.8 to be a Seyfert 1.0. At the same time, it underwent a strong increase of X-ray flux by one order of magnitude with respect to archival measurements. We characterise the X-ray spectral and timing properties of NGC 2617 with the aim of studying the physics of a changing-look active galactic nucleus (AGN).

Methods. We performed a comprehensive timing and spectral analysis of two XMM-Newton pointed observations spaced by one month, complemented by archival quasi-simultaneous INTEGRAL observations.

Results. We found that, to the first order, NGC 2617 looks like a type 1 AGN in the X-ray band and, with the addition of a modest reflection component, its continuum can be modelled well either with a power law plus a phenomenological blackbody, a partially covered power law, or a double Comptonisation model. Independent of the continuum adopted, in all three cases a column density of a few 10²³ cm^-2 of neutral gas covering 20–40% of the continuum source is required by the data. Most interestingly, absorption structures due to highly ionised iron have been detected in both observations with a redshift of about 0.1c with respect to the systemic redshift of the host galaxy.

Conclusions. The redshifted absorber can be ascribed to a failed wind/aborted jets component, to gravitational redshift effects, and/or to matter directly falling towards the central supermassive black hole. In either case, we are probing the innermost accretion flow around the central supermassive black hole of NGC 2617 and might be even watching matter in a direct inflow towards the black hole itself.