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