Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dramatic X-ray Spectral Variability of the Broad Absorption Line Quasar
  PG2112+059   With a 1999 ASCA observation, PG2112+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 PG2112+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
K alpha region has appeared. Concurrent 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
CIV 1549 BAL since 1992; however, the OVI BAL structure is consistent with a
1995 observation. We also present evidence for Ly beta--OVI 1037.62 and Ly
alpha--NV 1242.80 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 PG2112+059 suggests that X-ray
spectral variability studies of BAL quasars have great potential for probing
the physics of quasar winds.

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The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-ex
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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-th
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The categories of this paper are: supr-con
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The categories of this paper are: comp-gas
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The categories of this paper are: math
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The categories of this paper are: alg-geom
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The categories of this paper are: stat