Anatomy of the AGN in NGC 5548

VI. Long-term variability of the warm absorber

¹ XMM-Newton Science Operations Centre, ESAC, Camino Bajo del Castillo s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
e-mail: jebrero@sciops.esa.int
² SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
³ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
⁶ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
⁷ INAF–IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁸ Department of Astronomy, University of Geneva, 16 Ch. d’Ecogia, 1290 Versoix, Switzerland
⁹ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
¹⁰ University Grenoble Alpes, IPAG, 38000 Grenoble, France
¹¹ CNRS, IPAG, 38000 Grenoble, France
¹² Max-Planck-Institut für Extraterretrische Physik, Giessenbachstrasse, 85748 Garching, Germany
¹³ Astronomisches Institut, Ruhr-Universität Bochum, Universitätstrasse 150, 44801 Bochum, Germany
¹⁴ Department of Physics, 192-0397 Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, 192-0397 Tokyo, Japan
¹⁵ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Casilla 1280, Antofagasta, Chile

Received: 23 November 2015
Accepted: 5 January 2016

Abstract

Context. We observed the archetypal Seyfert 1 galaxy NGC 5548 in 2013−2014 in the context of an extensive multiwavelength campaign involving several satellites, which revealed the source to be in an extraordinary state of persistent heavy obscuration.

Aims. We re-analyzed the archival grating spectra obtained by XMM-Newton and Chandra between 1999 and 2007 in order to characterize the classic warm absorber (WA) using consistent models and up-to-date photoionization codes and atomic physics databases and to construct a baseline model that can be used as a template for the physical state of the WA in the 2013 observations.

Methods. We used the latest version of the photoionization code CLOUDY and the SPEX fitting package to model the X-ray grating spectra of the different archival observations of NGC 5548.

Results. We find that the WA in NGC 5548 is composed of six distinct ionization phases outflowing in four kinematic regimes. The components seem to be in the form of a stratified wind with several layers intersected by our line of sight. Assuming that the changes in the WA are solely due to ionization or recombination processes in response to variations in the ionizing flux among the different observations, we are able to estimate lower limits on the density of the absorbing gas, finding that the farthest components are less dense and have a lower ionization. These limits are used to put stringent upper limits on the distance of the WA components from the central ionizing source, with the lowest ionization phases at several pc distances (<50, <20, and <5 pc, respectively), while the intermediately ionized components lie at pc-scale distances from the center (<3.6 and <2.2 pc, respectively). The highest ionization component is located at ~0.6 pc or closer to the AGN central engine. The mass outflow rate summed over all WA components is ~0.3 M_⊙ yr^-1, about six times the nominal accretion rate of the source. The total kinetic luminosity injected into the surrounding medium is a small fraction (~0.03%) of the bolometric luminosity of the source. After adding the contribution of the UV absorbers, this value augments to ~0.2% of the bolometric luminosity, well below the minimum amount of energy required by current feedback models to regulate galaxy evolution.