Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017. (arXiv:1910.03609v1 [astro-ph.HE])
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We present a multiwavelength study of the flat-spectrum radio quasar CTA 102
during 2013-2017. We use radio-to-optical data obtained by the Whole Earth
Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and
103 GHz data from the Atacama Large Millimeter Array, near-infrared data from
the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and
X-rays) and Fermi ($gamma$ rays) satellites to study flux and spectral
variability and the correlation between flux changes at different wavelengths.
Unprecedented $gamma$-ray flaring activity was observed during 2016
November-2017 February, with four major outbursts. A peak flux of (2158 $pm$
63)$times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$, corresponding to a luminosity of
(2.2 $pm$ 0.1)$times$10$^{50}$ erg s$^{-1}$, was reached on 2016 December 28.
These four $gamma$-ray outbursts have corresponding events in the
near-infrared, optical and UV bands, with the peaks observed at the same time.
A general agreement between X-ray and $gamma$-ray activity is found. The
$gamma$-ray flux variations show a general, strong correlation with the
optical ones with no time lag between the two bands and a comparable
variability amplitude. This $gamma$-ray/optical relationship is in agreement
with the geometrical model that has successfully explained the low-energy flux
and spectral behaviour, suggesting that the long-term flux variations are
mainly due to changes in the Doppler factor produced by variations of the
viewing angle of the emitting regions. The difference in behaviour between
radio and higher-energy emission would be ascribed to different viewing angles
of the jet regions producing their emission.

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102
during 2013-2017. We use radio-to-optical data obtained by the Whole Earth
Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and
103 GHz data from the Atacama Large Millimeter Array, near-infrared data from
the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and
X-rays) and Fermi ($gamma$ rays) satellites to study flux and spectral
variability and the correlation between flux changes at different wavelengths.
Unprecedented $gamma$-ray flaring activity was observed during 2016
November-2017 February, with four major outbursts. A peak flux of (2158 $pm$
63)$times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$, corresponding to a luminosity of
(2.2 $pm$ 0.1)$times$10$^{50}$ erg s$^{-1}$, was reached on 2016 December 28.
These four $gamma$-ray outbursts have corresponding events in the
near-infrared, optical and UV bands, with the peaks observed at the same time.
A general agreement between X-ray and $gamma$-ray activity is found. The
$gamma$-ray flux variations show a general, strong correlation with the
optical ones with no time lag between the two bands and a comparable
variability amplitude. This $gamma$-ray/optical relationship is in agreement
with the geometrical model that has successfully explained the low-energy flux
and spectral behaviour, suggesting that the long-term flux variations are
mainly due to changes in the Doppler factor produced by variations of the
viewing angle of the emitting regions. The difference in behaviour between
radio and higher-energy emission would be ascribed to different viewing angles
of the jet regions producing their emission.

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