Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical and near-infrared photometric monitoring of the transient X-ray
  binary A0538-66 with REM   The transient Be/X-ray binary A0538-66 shows peculiar X-ray and optical
variability. Despite numerous studies, the intrinsic properties underlying its
anomalous behaviour remain poorly understood. Since 2014 September we are
conducting the first quasi-simultaneous optical and near-infrared photometric
monitoring of A0538-66 in seven filters with the Rapid Eye Mount (REM)
telescope, aiming to understand the properties of this binary system. We found
that the REM lightcurves show fast flares lasting one or two days that repeat
almost regularly every ~16.6 days, the orbital period of the neutron star. If
the optical flares are powered by X-ray outbursts through photon reprocessing,
the REM lightcurves indicate that A0538-66 is still active in X-rays: bright
X-ray flares (L_x > 1E37 erg/s) could be observable during the periastron
passages. The REM lightcurves show a long-term variability that is especially
pronounced in the g band and decreases with increasing wavelength, until it no
longer appears in the near-infrared lightcurves. In addition, A0538-66 is
fainter with respect to previous optical observations most likely due to the
higher absorption of the stellar radiation of a denser circumstellar disc. On
the basis of the current models, we interpret these observational results with
a circumstellar disc around the Be star observed nearly edge-on during a
partial depletion phase. The REM lightcurves also show short-term variability
on timescales of ~1 day possibly indicative of perturbations in the density
distribution of the circumstellar disc caused by the tidal interaction with the
neutron star.

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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: plasm-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: atom-ph
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: nlin
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci