Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vela X-1 as seen by RXTE   We present results from four observations of the accreting X-ray pulsar Vela
X-1 with RXTE in 1996 February.
  The light curves show strong pulse to pulse variations, while the average
pulse profiles are quite stable, similar to previous results. Below 5keV the
pulse profiles display a complex, 5-peaked structure with a transition to a
simple, double peak above about 15keV.
  We analyze phase-averaged, phase-resolved, and on-pulse minus off-pulse
spectra. The best spectral fits were obtained using continuum models with a
smooth high-energy turnover. In contrast, the commonly used power law with
exponential cutoff introduced artificial features in the fit residuals. Using a
power law with a Fermi-Dirac cutoff modified by photoelectric absorption and an
iron line, the best fit spectra are still unacceptable. We interpret large
deviations around 25 and 55keV as fundamental and second harmonic cyclotron
absorption lines. If this result holds true, the ratio of the line energies
seems to be larger than 2. Phase resolved spectra show that the cyclotron lines
are strongest on the main pulse while they are barely visible outside the
pulses.

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The categories of this paper are: adap-org
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: math
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: hep-lat
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The categories of this paper are: cs
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: mtrl-th
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The categories of this paper are: stat
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The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th