Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Variable Warm Absorber in Circinus X-1   We observed Circinus X-1 twice during a newly reached low-flux phase near
zero orbital phase using the High-Energy Transmission Grating Spectrometer
(HETGS) onboard Chandra. In both observations the source did not show the P
Cygni lines we observed during the high-flux phases of the source in 2000 and
2001. During pre-zero phase the source did not exhibit significant variability
and exhibited an emission-line spectrum rich in H- and He-like lines from high
Z elements such as Si, S, Ar, and Ca. We analyzed all high resolution X-ray
spectra by fitting photoionization and absorption models from the most recent
version of the XSTAR code. The pre-zero phase spectrum could be fully modeled
with a very hot photoionized plasma with an ionization parameter of log xi =
3.0. Post-zero phase episodes feature absorbers with variable high columns,
ionization parameter, and luminosity. While cold absorption remains at levels
quite similar to the one observed in previous years, the new observations show
unprecedented levels of variable warm absorption. The line emissivities also
indicate that the observed low source luminosity is inconsistent with a static
hot accretion disk corona (ADC), an effect that seems common to other near
edge-on ADC sources as well. We conclude that unless there exists some means of
coronal heating other than X-rays, the true source luminosity is likely much
higher and we observe obscuration in analogy to the extragalactic Seyfert II
sources. We discuss possible consequences and relate cold, luke-warm, warm, and
hot absorbers to dynamic accretion scenarios.

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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: math
34
The categories of this paper are: chem-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin