Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasi-periodic behaviour in the optical and {\gamma}-ray light curves of
  blazars 3C 66A and B2 1633+38   We report on quasi-periodic variability found in two blazars included in the
Steward Observatory Blazar Monitoring data sample: the BL Lac object 3C 66A and
the Flat Spectrum Radio Quasar B2 1633+38. We collect optical photometric and
polarimetric data in V and R bands of these sources from different
observatories: St. Petersburg University, Crimean Astrophysical Observatory,
WEBT-GASP, Catalina Real-Time Transient Survey, Steward Observatory, STELLA
Robotic Observatory and Katzman Automatic Imaging Telescope. In addition, an
analysis of the $\gamma$-ray light curves from $\textit{Fermi}$-LAT is
included. Three methods are used to search for any periodic behaviour in the
data: the Z-transform Discrete Correlation Function, the Lomb-Scargle
periodogram and the Weighted Wavelet Z-transform. We find evidences of possible
quasi-periodic variability in the optical photometric data of both sources with
periods of $\sim$3 years for 3C 66A and $\sim$1.9 years for B2 1633+38, with
significances between 3$\sigma$ and 5$\sigma$. Only B2 1633+38 shows evidence
of this behaviour in the optical polarized data set at a confidence level of
2$\sigma$-4$\sigma$. This is the first reported evidence of quasi-periodic
behaviour in the optical light curve of B2 1633+38. Also a hint of
quasi-periodic behaviour is found in the $\gamma$-ray light curve of B2 1633+38
with a confidence level $\geqslant$2$\sigma$, while no periodicity is observed
for 3C 66A in this energy range. We propose different jet emission models that
could explain the quasi-periodic variability and the differences found between
these two sources.

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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: stat
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The categories of this paper are: cs
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: cond-mat
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The categories of this paper are: eess