The X‐Ray Warm Absorber in NGC 3516

Abstract

The Seyfert 1 galaxy, NGC 3516 has been the subject of many absorption line studies at both ultraviolet and X-ray wavelengths. In the UV, strong, broad, variable associated metal line absorption with velocity width ~2000 km s-1 is thought to originate in gas with NH gsim 1019 cm-2 lying between 0.01 and 9 pc from the central active nucleus. The Ginga X-ray data are consistent with several possibilities: a warm absorber and a cold absorber combined either with partial covering or an unusually strong reflection spectrum. We present ROSAT observations of NGC 3516 which show a strong detection of a warm absorber dominated by a blend of O VII/O VIII edges at ~0.8 keV with NH ~ 7 × 1021 cm-2 and U:8-12. We argue that NGC 3516 contains an outflowing "XUV" absorber showing the presence of X-ray absorption edges which are consistent with the presence of broad absorption lines in the old IUE spectra and their disappearance in the new UV observations. Our dynamical model suggests that the O VII absorption edge will continue to weaken compared to the O VIII edge, an easily testable prediction with future missions like AXAF. Eventually the source would be transparent to the X-rays unless a new absorption system is produced.