Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Intrinsically X-ray Weak Quasar PHL 1811. I. X-ray Observations and
  Spectral Energy Distribution   This is the first of two papers reporting observations and analysis of the
unusually bright (m_b=14.4), luminous (M_B=-25.5), nearby (z=0.192) narrow-line
quasar PHL 1811, focusing on the X-ray properties and the spectral energy
distribution. Two Chandra observations reveal a weak X-ray source with a steep
spectrum. Variability by a factor of 4 between the two observations separated
by 12 days suggest that the X-rays are not scattered emission. The XMM-Newton
spectra are modelled in the 0.3--5 keV band by a steep power law with \Gamma =
2.3\pm 0.1, and the upper limit on intrinsic absorption is 8.7 x 10^{20}
cm^{-2}. The spectral slopes are consistent with power law indices commonly
observed in NLS1s, and it appears that we observe the central engine X-rays
directly. Including two recent Swift ToO snapshots, a factor of ~5 variability
was observed among the five X-ray observations reported here. In contrast, the
UV photometry obtained by the XMM-Newton OM and Swift UVOT, and the HST
spectrum reveal no significant UV variability. The \alpha_{ox} inferred from
the Chandra and contemporaneous HST spectrum is -2.3 \pm 0.1, significantly
steeper than observed from other quasars of the same optical luminosity. The
steep, canonical X-ray spectra, lack of absorption, and significant X-ray
variability lead us to conclude that PHL 1811 is intrinsically X-ray weak. We
also discuss an accretion disk model, and the host galaxy of PHL 1811.

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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: q-bio
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
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The categories of this paper are: stat
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The categories of this paper are: physics
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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: q-fin
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: funct-an