Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evidence for X-ray Obscuration in Type II Quasar Candidates from the
  Sloan Digital Sky Survey   Recently, Zakamska et al. (2003) selected 291 high-ionization narrow
emission-line AGN in the redshift range 0.3-0.83 from the Sloan Digital Sky
Survey spectroscopic data. The sample includes both Seyfert II galaxies and
their higher luminosity "cousins", Type II quasar candidates. Here we present
the results on the X-ray properties of 17 of these objects for which archival
X-ray data (ROSAT and XMM-Newton) are available. Three sources have been
significantly (>6 sigma) detected, one being the most radio-loud source of the
sample; its X-ray emission, possibly enhanced by jet emission, is consistent
with the absence of absorption. Another source has a ~6 sigma detection in the
ROSAT All-Sky Survey, possibly complex radio structure, and no evidence for
strong X-ray absorption. For the third X-ray detection, the XMM-Newton spectrum
indicates a column density of NH=1.26+0.75/-0.51x10^22 cm^-2; this result,
coupled with the 2-10 keV luminosity of ~4x10^44 cgs, makes this source a
genuine Type II quasar. Using the O[III]5007 line luminosities, we estimated
the intrinsic X-ray power of the AGN and found that >47% of the observed sample
shows indications of X-ray absorption, with column densities >10^22 cm^-2. This
provides further evidence that a considerable fraction are obscured quasars.
Support to our conclusions also comes from the recent analysis of RASS data
performed by Zakamska et al. (2004), who found five additional lower
significance (~2.1-3.6 sigma) X-ray matches.

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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: econ
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The categories of this paper are: cond-mat
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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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: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: atom-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: math