The warm absorber in NGC 5548 : the lean years

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 K 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 K line flux does enable a unique explanation to be derived.