The X‐Ray Warm Absorber in NGC 3516

The Seyfert 1 galaxy, NGC3516 has been the subject of many absorption linestudies at both ultraviolet and X-ray wavelengths. In the UV, strong, broad,variable associated metal line absorption with velocity width $\sim 2000$ \kms\is thought to originate in gas with nh larger than about $10^{19}$ cm$^{-2}$lying between 0.01 and 9 pc from the central active nucleus. The Ginga X-raydata are consistent with several possibilities: a warm absorber and a coldabsorber combined either with partial covering or an unusually strongreflection spectrum. We present ROSAT observations of NGC3516 which show astrong detection of a warm absorber dominated by a blend of OVII/OVIII edges at$\sim$ 0.8 keV with nh $\sim 7\times 10^{21}$ cm$^{-2}$ and U: 8--12. We arguethat NGC3516 contains an outflowing `XUV' absorber showing the presence ofX-ray absorption edges, that are consistent with the presence of broadabsorption lines in the old IUE spectra and their disappearance in the new UVobservations. Our dynamical model suggests that the OVII absorption edge willcontinue to weaken compared to the OVIII edge, an easily testable predictionwith future missions like AXAF. Eventually the source would be transparent tothe X-rays unless a new absorption system is produced.Comment: 24 pages with 5 figures. To appear in the Ap.J. Requires AAS macro