The warm absorber in NGC 5548

The lean years

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: r.g.detmers@sron.nl
² Astronomical Institute, University of Utrecht, Postbus 80000, 3508 TA Utrecht, The Netherlands
³ School of Physics and Astronomy, The University, Southampton SO17 1BJ, UK

Received: 27 March 2008
Accepted: 16 April 2008

Abstract

We study the variability of the warm absorber and the gas responsible for the emission lines in the Seyfert 1 galaxy NGC 5548 to constrain the location and physical properties of these components. Using X-ray spectra acquired using the Chandra-LETGS in 2002 and 2005, we study the variability of the ionic column densities and line intensities. We measure a lower  forbidden emission line flux in 2005, while the Fe Kα line flux remains constant. The warm absorber is less ionized in 2005, which enbles its location to be constrained to within 7 pc of the central source. Using both the observed variability and the limit on the FWHM of the  f line, we constrain the location of the narrow line region to a distance of 1 pc from the central source. The apparent lack of variability in the Fe Kα line flux does enable a unique explanation to be derived.