Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Strong Aperiodic X-ray Variability and Quasi-Periodic Oscillation in
  X-ray Nova XTE J1550-564   We report the discovery of strong aperiodic X-ray variability and
quasi-periodic oscillation (QPO) in the X-ray light curves of a new X-ray Nova,
XTE J1550-564, and the evolution of the observed temporal properties during the
rise of the recent X-ray outburst. The power spectral analysis of the first
observation reveals strong aperiodic X-ray variability of the source (~28%), as
well as the presence of a QPO at ~82 mHz with fractional rms amplitude ~14%
over the 2-60 keV energy range. Also apparent is the first harmonic of the QPO
with the amplitude ~9%. As the X-ray flux increases, the source tends to become
less variable, and the QPO frequency increases rapidly, from 82 mHz to 4 Hz,
over the flux (2-50 keV) range of 1.73-5.75 x 10^{-8} ergs cm^{-2} s^{-1}. The
amplitude of the fundamental component of the QPO varies little, while that of
the harmonic follows a decreasing trend. The fundamental component strengthens
toward high energies, while its harmonic weakens. Initially, the power spectrum
is roughly flat at low frequencies and turns into a power law at high
frequencies, with the QPO harmonic sitting roughly at the break. In later
observations, however, the high-frequency portion of the continuum can actually
be better described by a broken power law (as opposed to a simple power law).
This effect becomes more apparent at higher energies. The overall amplitude of
the continuum shows a similar energy dependence to that of the fundamental
component of the QPO. Strong rapid X-ray variability, as well as hard energy
spectrum, makes XTE J1550-564 a good black hole candidate. We compare its
temporal properties with those of other black hole candidates.

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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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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: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: cmp-lg
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: nucl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: acc-phys