Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Associating long-term gamma-ray variability with the superorbital period
  of LS I 61 303   Gamma-ray binaries are stellar systems for which the spectral energy
distribution (discounting the thermal stellar emission) peaks at high energies.
Detected from radio to TeV gamma rays, the gamma-ray binary LS I 61 303 is
highly variable across all frequencies. One aspect of this system's variability
is the modulation of its emission with the timescale set by the ~26.4960-day
orbital period. Here we show that, during the time of our observations, the
gamma-ray emission of LS I 61 303 also presents a sinusoidal variability
consistent with the previously-known superorbital period of 1667 days. This
modulation is more prominently seen at orbital phases around apastron, whereas
it does not introduce a visible change close to periastron. It is also found in
the appearance and disappearance of variability at the orbital period in the
power spectrum of the data. This behavior could be explained by a
quasi-cyclical evolution of the equatorial outflow of the Be companion star,
whose features influence the conditions for generating gamma rays. These
findings open the possibility to use gamma-ray observations to study the
outflows of massive stars in eccentric binary systems.

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The categories of this paper are: funct-an
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The categories of this paper are: gr-qc
18
The categories of this paper are: econ
0
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: hep-lat
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The categories of this paper are: hep-th
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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: nucl-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys