An ExploratoryChandraSurvey of a Well‐defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars

Abstract

We present 4–7 ks Chandra observations of 35 broad absorption line (BAL) quasars from the Large Bright Quasar Survey, the largest sample of sensitive, 0.5–8.0 keV X-ray observations of this class of quasars to date. The limitedrangesinbothredshift(z ¼ 1:42 2:90)andultravioletluminosity(afactorof � 12)ofthesamplealsomake itrelativelyuniform.Of 35 targets,27 aredetected fora detectionfractionof 77%, and we confirmprevious studies that find BAL quasars to be generally X-ray-weak. Five of the eight nondetections are known low-ionization BAL quasars, confirming reports of extreme X-ray weakness in this subset (� 10% of optically selected BAL quasars). ThoseBALquasarswiththehardestX-rayspectraarealsotheX-rayweakest,consistentwiththeinterpretationthat intrinsic absorption is the primary cause of X-ray weakness in this class of quasars as a whole. Furthermore, the observed trend is not consistent with simple neutral absorption, supporting findings from spectroscopic observations of individual targets that BAL quasars typically exhibit complex X-ray absorption (e.g., partially covering orionizedabsorbers).AssumingnormalquasarX-raycontinuaandusingthehard-band(observed-frame2–8keV) X-ray flux to ‘‘correct’’ for the effects of intrinsic absorption at softer energies increases the relative X-ray to optical flux ratios to much closer to the range for normal quasars, further indicating that typically neither are highionizationBALquasarsintrinsicallyX-ray-weak,nordotheysufferfromCompton-thickabsorption.Ingeneral,we find no evidence for correlations between X-ray weakness and ultraviolet absorption-line properties, with the exception of a likely correlation between the maximum outflow velocity of C iv absorption and the magnitude of X-ray weakness. We discuss the implications of our results for disk-wind models of BAL outflows in quasars. Subject headingg galaxies: active — quasars: absorption lines — quasars: general — X-rays: galaxies