Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: BeppoSAX observation of the X-ray binary pulsar Vela X-1   We report on the spectral (pulse averaged) and timing analysis of the ~ 20
ksec observation of the X-ray binary pulsar Vela X-1 performed during the
BeppoSAX Science Verification Phase. The source was observed in two different
intensity states: the low state is probably due to an erratic intensity dip and
shows a decrease of a factor ~ 2 in intensity, and a factor 10 in Nh. We have
not been able to fit the 2-100 keV continuum spectrum with the standard (for an
X--ray pulsar) power law modified by a high energy cutoff because of the
flattening of the spectrum in ~ 10-30 keV. The timing analysis confirms
previous results: the pulse profile changes from a five-peak structure for
energies less than 15 keV, to a simpler two-peak shape at higher energies. The
Fourier analysis shows a very complex harmonic component: up to 23 harmonics
are clearly visible in the power spectrum, with a dominant first harmonic for
low energy data, and a second one as the more prominent for energies greater
than 15 keV. The aperiodic component in the Vela X-1 power spectrum presents a
knee at about 1 Hz. The pulse period, corrected for binary motion, is 283.206
+/- 0.001 sec.

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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ph
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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: physics
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: math
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The categories of this paper are: dg-ga