Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: RXTE monitoring of Centaurus A   We report on the analysis from ~110 ks of X-ray observations of Centaurus A
carried out with the Proportional Counter Array (PCA) and the High Energy X-ray
Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE)
during three monitoring campaigns over the last 4 years (10 ks in 1996, 74 ks
in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well
described by a heavily absorbed power law with photon index 1.8 and a narrow
iron line due to fluorescence of cold matter. The measured column depth
decreased by about 30% between 1996 and 2000, while the detected 2-10 keV
continuum flux remained constant between 1996 and 1998, but increased by 60% in
2000. Since in all three observations the iron line flux did not vary, a
corresponding decrease in equivalent width was noted. No appreciable evidence
for a reflection continuum in the spectrum was detected. We present the
interpretation of the iron line strength through Monte Carlo computations of
various geometries. No significant temporal variability was found in Cen A at
time scales from days to tens of minutes.

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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: cs
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn