Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-raying the Ultraluminous Infrared Starburst Galaxy and Broad
  Absorption Line QSO, Markarian 231, with Chandra   With 40 ks of Chandra ACIS-S3 exposure, new information on both the starburst
and QSO components of the X-ray emission of Markarian 231, an ultraluminous
infrared galaxy and Broad Absorption Line QSO, has been obtained. The bulk of
the X-ray luminosity is emitted from an unresolved nuclear point source, and
the spectrum is remarkably hard with the majority of the flux emitted above 2
keV. Most notably, significant nuclear variability (a decrease of ~45% in
approximately 6 hours) at energies above 2 keV indicates that Chandra has
probed within light hours of the central black hole. Though we concur with
Maloney & Reynolds that the direct continuum is not observed, this variability
coupled with the 188 eV upper limit on the equivalent width of the FeKalpha
emission line argues against the reflection-dominated model put forth by these
authors based on their ASCA data. Instead, we favor a model in which a small,
Compton-thick absorber blocks the direct X-rays, and only indirect, scattered
X-rays from multiple lines of sight can reach the observer. Extended soft,
thermal emission encompasses the optical extent of the galaxy and exhibits
resolved structure. An off-nuclear X-ray source with a 0.35-8.0 keV luminosity
of L_X=7x10^{39} erg s^{-1}, consistent with the ultraluminous X-ray sources in
other nearby starbursts, is detected. We also present an unpublished FOS
spectrum from the HST archive showing the broad C IV absorption.

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The categories of this paper are: math-ph
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: hep-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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The categories of this paper are: cs
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The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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The categories of this paper are: chem-ph
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The categories of this paper are: eess