Volume 592, August 2016
|Number of page(s)||18|
|Published online||07 July 2016|
Anatomy of the AGN in NGC 5548
VIII. XMM-Newton’s EPIC detailed view of an unexpected variable multilayer absorber
1 INAF–IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
2 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
3 Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
4 Université Grenoble Alpes, IPAG, 38000 Grenoble, France
5 CNRS, IPAG, 38000 Grenoble, France
6 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
7 Department of Physics and Astronomy, Universiteit Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands
8 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
9 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
10 Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
11 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
12 Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
13 Department of Physics, Technion-Israel Institute of Technology, 32000 Haifa, Israel
14 Department of Astronomy, University of Geneva, 16 Chemin d’Ecogia, 1290 Versoix, Switzerland
15 European Space Astronomy Centre, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
16 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
17 Department of Astronomy, The Ohio State University, 140 W 18th Avenue, Columbus, OH 43210, USA
18 Center for Cosmology & AstroParticle Physics, The Ohio State University, 191 West Woodruff Ave., Columbus, OH 43210, USA
19 Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, 1280 Casilla, Antofagasta, Chile
20 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Received: 9 March 2016
Accepted: 5 April 2016
In 2013, we conducted a large multi-wavelength campaign on the archetypical Seyfert 1 galaxy NGC 5548. Unexpectedly, this usually unobscured source appeared strongly absorbed in the soft X-rays during the entire campaign, and signatures of new and strong outflows were present in the almost simultaneous UV HST/COS data. Here we carry out a comprehensive spectral analysis of all available XMM-Newton observations of NGC 5548 (precisely 14 observations from our campaign plus three from the archive, for a total of ~763 ks) in combination with three simultaneous NuSTAR observations. We obtain a best-fit underlying continuum model composed by i) a weakly varying flat (Γ ~ 1.5–1.7) power-law component; ii) a constant, cold reflection (FeK + continuum) component; iii) a soft excess, possibly owing to thermal Comptonization; and iv) a constant, ionized scattered emission-line dominated component. Our main findings are that, during the 2013 campaign, the first three of these components appear to be partially covered by a heavy and variable obscurer that is located along the line of sight (LOS), which is consistent with a multilayer of cold and mildly ionized gas. We characterize in detail the short timescale (mostly ~ks-to-days) spectral variability of this new obscurer, and find it is mostly due to a combination of column density and covering factor variations, on top of intrinsic power-law (flux and slope) variations. In addition, our best-fit spectrum is left with several (but marginal) absorption features at rest-frame energies ~6.7−6.9 keV and ~8 keV, aswell as a weak broad emission line feature redwards of the 6.4 keV emission line. These could indicate a more complex underlying model, e.g. a P-Cygni-type emission profile if we allow for a large velocity and wide-angle outflow. These findings are consistent with a picture where the obscurer represents the manifestation along the LOS of a multilayer of gas, which is also in multiphase, and which is likely outflowing at high speed, and simultaneously producing heavy obscuration and scattering in the X-rays, as well as broad absorption features in the UV.
Key words: galaxies: active / X-rays: galaxies / galaxies: individual: NGC 5548
© ESO, 2016
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