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Issue A&A
Volume 488, Number 1, September II 2008
Page(s) 67 - 72
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:200809862
Published online 16 June 2008



A&A 488, 67-72 (2008)
DOI: 10.1051/0004-6361:200809862

The warm absorber in NGC 5548

The lean years
R. G. Detmers1, J. S. Kaastra1, 2, E. Costantini1, I. M. McHardy3, and F. Verbunt2

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 $\ion{O}{vii}$ forbidden emission line flux in 2005, while the Fe K$\alpha$ 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 $\ion{O}{vii}$ 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$\alpha$ line flux does enable a unique explanation to be derived.


Key words: galaxies: active -- techniques: spectroscopic -- galaxies: Seyfert -- X-rays: individuals: NGC 5548



© ESO 2008

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