The Long-Term X-Ray Variability of Broad Absorption Line Quasars

TL;DR

This study investigates the long-term X-ray variability of eleven BAL quasars over 3-30 years, revealing significant variability in some sources and providing insights into the stability of the shielding gas involved in BAL wind launching.

Contribution

It presents the first comprehensive long-term X-ray variability analysis of BAL quasars, including new Chandra observations and spectral variability insights.

Findings

Significant X-ray variability detected in three quasars.

Maximum flux variability factors up to 9.9 observed.

No evidence of common strong changes in shielding gas over time.

Abstract

We analyze the long-term (rest-frame 3-30 yr) X-Ray variability of eleven broad absorption line (BAL) quasars, mainly to constrain the variation properties of the X-Ray absorbing shielding gas that is thought to play a critical role in BAL wind launching. Our BAL quasar sample has coverage with multiple X-ray observatories including Chandra, XMM-Newton, BeppoSAX, ASCA, ROSAT, and Einstein; 3-11 observations are available for each source. For seven of the eleven sources we have obtained and analyzed new Chandra observations suitable for searching for any strong X-ray variability. We find highly significant X-Ray variability in three sources (PG 1001+054, PG 1004+130, and PG 2112+059). The maximum observed amplitude of the 2-8 keV variability is a factor of $3.8\pm 1.3$, $1.5\pm 0.2$, and $9.9\pm 2.3$ for PG 1001+054, PG 1004+130, and PG 2112+059, respectively, and these sources show detectable variability on rest-frame timescales down to 5.8, 1.4, and 0.5 yr. For PG 1004+130 and PG 2112+059 we also find significant X-Ray spectral variability associated with the flux variability. Considering our sample as a whole, we do not find that BAL quasars exhibit exceptional long-term X-Ray variability when compared to the quasar population in general. We do not find evidence for common strong changes in the shielding gas owing to physical rearrangement or accretion-disk rotation, although some changes are found; this has implications for modeling observed ultraviolet BAL variability. Finally, we report for the first time an X-Ray detection of the highly polarized and well-studied BAL quasar IRAS 14026+4341 in its new Chandra observation.