Anatomy of the AGN in NGC 5548. VIII. XMM-Newton's EPIC detailed view of an unexpected variable multilayer absorber

Journal
Date Issued
2016
Author(s)
•
De Marco, B.
•
•
•
Petrucci, P. -O.
•
Bianchi, S.
•
Kaastra, J. S.
•
Kriss, G. A.
•
Mehdipour, M.
•
Whewell, M.
•
Arav, N.
•
Behar, E.
•
Boissay, R.
•
Branduardi-Raymont, G.
•
Costantini, E.
•
Ebrero, J.
•
Di Gesu, L.
•
Harrison, F. A.
•
Kaspi, S.
•
Matt, G.
•
Paltani, S.
•
Peterson, B. M.
•
Steenbrugge, K. C.
•
Walton, D. J.
DOI
Abstract
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.
Volume
592
Start page
A27
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2016A&A...592A..27C
Rights
open.access
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