Exploratory Study of the X‐Ray Properties of Quasars with Intrinsic Narrow Absorption Lines

Abstract

We have used archival Chandra and XMM-Newton observations of quasars hosting intrinsic narrow UV absorption lines (intrinsic NALs) to carry out an exploratory survey of their X-ray properties. Our sample consists of three intrinsic NAL quasars and one mini-BAL quasar, plus four quasars without intrinsic absorption lines for comparison. These were drawn in a systematic manner from an optical/UV-selected sample. The X-ray properties of intrinsic NAL quasars are indistinguishable from those of normal quasars. We do not find any excess absorption in quasars with intrinsic NALs, with upper limits of -->NH few × 1022 cm −2. We compare the X-ray and UV properties of our sample quasars by plotting the equivalent width and blueshift velocity of the intrinsic NALs and the X-ray spectral index against the optical-to-X-ray slope, -->αox. When BAL quasars and other AGNs with intrinsic NALs are included, the plots suggest that intrinsic NAL quasars form an extension of the BAL sequences and tend to bridge the gap between BAL and normal quasars. Observations of larger samples of intrinsic NAL quasars are needed to verify these conclusions. We also test two competing scenarios for the location of the NAL gas in an accretion disk wind. Our results strongly support a location of the NAL gas at high latitudes above the disk, closer to the disk axis than the dense BAL wind. We detect excess X-ray absorption only in Q0014+8118, which does not host intrinsic NALs. The absorbing medium very likely corresponds to an intervening system at -->z = 1.1, which also produces strong absorption lines in the rest-frame UV spectrum of this quasar. In an appendix we discuss the connection between UV and X-ray attenuation and its effect on -->αox.