X-ray spectroscopy of NGC 5548

Abstract

We analyze the high-resolution X-ray spectrum of the Seyfert 1 galaxy NGC 5548, for the full 0.1-10 keV band, using improved calibration results of the Chandra-LETGS instrument. The warm absorber consists of at least three ionization components, namely one with a low, medium and high ionization parameter. The X-ray absorbing material, from an outflowing wind, covers the full range of velocity components found from UV absorption lines. The presence of redshifted emission components for the strongest blue-shifted resonance absorption lines indicate that the absorber is located at a distance larger than the edge of the accretion disk. We derive an upper limit to the edge of the accretion disk of 1 light year. Absorption lines from ions of at least ten chemical elements have been detected, and in general for these elements there are no strong deviations from solar abundances. The narrow emission lines from the O VII and Ne IX forbidden and intercombination lines probably originate from much larger distances to the black hole. We find evidence for weak relativistically broadened oxygen and nitrogen emission lines from the inner parts of the accretion disk, but at a much smaller flux level than those observed in some other active galactic nuclei. In addition, there is a broad, non-relativistic C VI Ly alpha emission line that is consistent with emission lines from the inner part of the optical/UV broad line region.