Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The fundamental cyclotron line in 4U 1538-52   We present pulse phase averaged spectra of the high mass X-ray binary pulsar
4U 1538-52/QV Nor. Observations of this persistent accreting pulsar were made
with the Rossi X-ray Timing Explorer (RXTE). We study the variability of
cyclotron resonant scattering feature (CRSF or simply cyclotron line) in the
high energy spectra of this binary system. We show that the parameters of the
CRSF are correlated. The first one is, as suggested by theory, between the
width and the energy of the cyclotron line. The second one is between the
relative width and the optical depth of the cyclotron line. We discuss these
results with studies of other X-ray pulsars and their implications on the line
variability.

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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: gr-qc
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
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The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: cond-mat