X-ray narrow line region variability as a geometry probe

The case of NGC 5548

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, University of Southampton, Southampton SO17 1BJ, UK

Received: 9 January 2009
Accepted: 7 July 2009

Abstract

We study the long time scale variability of the gas responsible for the X-ray narrow emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the location and geometry of the emitting gas. Using X-ray spectra taken with the Chandra-LETGS and HETGS instruments and with XMM-Newton RGS and combining them with long-term monitoring observations of the Rossi X-ray Timing Explorer (RXTE), we perform a correlation analysis in order to try to constrain the time scale on which the narrow line emitting gas responds to variations of the continuum flux. With the inclusion of the 2007 Chandra-LETGS observation we have an additional observation at an historically low flux level. We conclude that the NLR in NGC 5548 is in the form of an ionization cone, compact in size, and located between 1 and 15 pc from the central source, depending on the exact geometry of the NLR.