Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The XMM-Newton/2dF survey IV. The X-ray spectral properties of the hard
  sources   We present an analysis of the X-ray spectral properties of 61 hard X-ray
selected (2-8 keV) sources from the bright ($f_{2-8 keV}>10^{-14}$ \funits)
{\it XMM-Newton}/2dF survey. This comprises of 9 {\it XMM-Newton} pointings in
the North Galactic Pole region ($\sim 1.6 \rm deg^2$) and overlaps with the
SDSS, 2QZ and 2dFGRS surveys. Our sources contribute about 50 per cent of the
2-10 keV X-ray background down to the flux limit of $10^{-14}$ cgs. The
hardness ratio distribution of the sample suggests a deficit of heavily
absorbed sources. A spectral fit to the co-added total source spectrum yields a
steep photon index, $\Gamma=1.83^{+0.04}_{-0.05}$. All but 8 sources have
optical counterparts down to the SDSS photometric limit of $r\approx22.5$.
Spectroscopic identifications exist for 34 sources. The vast majority are
associated with Broad-Line (BL) AGN (24 sources) while only 7 present narrow or
no emission lines. Five sources are probably associated with Galactic stars.
Finally, for another 17 probable AGN we present photometric redshifts. The
combined spectrum of the 24 spectroscopically identified BL AGN is steep
($\Gamma=2.02^{+0.04}_{-0.05}$), while that of the 7 AGN, which do not present
broad lines is flatter with $\Gamma=1.64^{+0.11}_{-0.11}$. The spectrum of the
8 optically unidentified sources is flat with $\Gamma\approx 1.1$. Spectral
fits to the individual BL AGN reveal large absorption (rest-frame column
density $\rm>10^{22} cm^{-2}$) in only two cases.
  The individual spectra of the NL AGN present significant evidence for even a
moderate absorption ($\rm 3\times 10^{21} cm^{-2}$) in only one case.

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The categories of this paper are: quant-ph
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The categories of this paper are: q-fin
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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: physics
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: ao-sci