Dramatic X‐Ray Spectral Variability of the Broad Absorption Line Quasar PG 2112+059

Abstract

With a 1999 ASCA observation, PG 2112+059 became notable as the first broad absorption line (BAL) quasar found to exhibit a typical radio-quiet quasar X-ray continuum underlying a large amount of intrinsic absorption. We present a recent Chandra ACIS-S3 observation of PG 2112+059 that demonstrates remarkable spectral and luminosity variability since that time. In addition to a decrease in the continuum normalization by a factor of ~3.5, the absorption column density has apparently increased substantially, and a strong feature in the Fe Kα region has appeared. Concurrent Hubble Space Telescope (HST) STIS data compared with archival HST data from earlier epochs show evidence for variability of the continuum (up to a factor of ~1.7 in the ultraviolet), and in some absorption features of the C IV λ1549 BAL since 1992; however, the O VI BAL structure is consistent with a 1995 observation. We also present evidence for Lyβ-O VI λ1037.62 and Lyα-N V λ1242.80 line-locked absorption systems, supporting the assumption that ultraviolet line pressure is driving the BAL outflow. Whereas ultraviolet BALs typically exhibit only modest equivalent width variability over timescales of years, the dramatic X-ray variability of PG 2112+059 suggests that X-ray spectral variability studies of BAL quasars have great potential for probing the physics of quasar winds.