Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observational signatures of X-ray irradiated accretion disks   Reflection of X-rays from cool material around a black hole is one of the few
observational diagnostics of the accretion flow geometry. Models of this
reflected spectrum generally assume that the accretion disk can be
characterized by material in a single ionization state. However, several
authors have recently stressed the importance of the classic ionization
instability for X-ray irradiated gas in hydrostatic balance. This instability
leads to a discontinuous transition in the vertical structure of the disk,
resulting in a hot ionized skin above much cooler material. If the Compton
temperature of the skin is high then even iron is completely ionized, and the
skin does not produce any spectral features. These new models, where the
ionization structure of the disk is calculated self-consistently, require an
excessive amount of computing power and so are difficult to use in directly
fitting observed X-ray spectra. Instead, we invert the problem by simulating
X-ray spectra produced by the new reflection models, and then fit these with
the old, single zone reflection models, to assess the extent to which the
derived accretion geometry depends on the reflection model used. We find that
the single zone ionization models can severely underestimate the covering
fraction of the ``cold'' material as seen from the X-ray source if the optical
depth in the ionized skin is of order unity, and that this can produce an
apparent correlation between the covering fraction and the X-ray spectral index
similar in nature to that reported by Zdziarski, Lubinski and Smith (1999).

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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: q-alg
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-th
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The categories of this paper are: solv-int
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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: gr-qc
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: quant-ph