The complex variability of blazars: time-scales and periodicity analysis in S4 0954+65
Date Issued
2021
Author(s)
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Larionov, V M
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Jorstad, S G
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Marscher, A P
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Weaver, Z R
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Acosta-Pulido, J A
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Agudo, I
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Andreeva, T
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Arkharov, A
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Bachev, R
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Benítez, E
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Berton, M
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Björklund, I
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Borman, G A
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Bozhilov, V
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Carosati, D
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Casadio, C
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Chen, W P
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Damljanovic, G
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Escudero, J
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Fuentes, A
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Grishina, T S
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Gupta, A C
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Hagen-Thorn, V A
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Hart, M
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Hiriart, D
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Hou, W-J
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Ivanov, D
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Kim, J-Y
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Kimeridze, G N
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Konstantopoulou, C
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Kopatskaya, E N
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Kurtanidze, O M
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Kurtanidze, S O
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Lähteenmäki, A
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Larionova, E G
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Larionova, L V
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Markovic, G
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Minev, M
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Morozova, D A
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Myserlis, I
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Nakamura, M
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Nikiforova, A A
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Nikolashvili, M G
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Otero-Santos, J
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Ovcharov, E
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Pursimo, T
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Rahimov, I
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Sakamoto, T
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Savchenko, S S
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Semkov, E H
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Shakhovskoy, D
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Sigua, L A
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Stojanovic, M
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Strigachev, A
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Thum, C
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Tornikoski, M
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Traianou, E
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Troitskaya, Y V
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Troitskiy, I S
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Tsai, A
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Valcheva, A
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Vasilyev, A A
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Vince, O
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Zaharieva, E
Abstract
Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019-2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole Earth Blazar Telescope (WEBT) Collaboration. The 2-min cadence optical light curves provided by TESS during three observing sectors of nearly 1 month each allow us to study the fast variability in great detail. We identify several characteristic short-term time-scales, ranging from a few hours to a few days. However, these are not persistent, as they differ in the various TESS sectors. The long-term photometric and polarimetric optical and radio monitoring undertaken by the WEBT brings significant additional information, revealing that (i) in the optical, long-term flux changes are almost achromatic, while the short-term ones are strongly chromatic; (ii) the radio flux variations at 37 GHz follow those in the optical with a delay of about 3 weeks; (iii) the range of variation of the polarization degree and angle is much larger in the optical than in the radio band, but the mean polarization angles are similar; (iv) the optical long-term variability is characterized by a quasi-periodicity of about 1 month. We explain the source behaviour in terms of a rotating inhomogeneous helical jet, whose pitch angle can change in time.
Volume
504
Issue
4
Start page
5629
Issn Identifier
0035-8711
Ads BibCode
2021MNRAS.504.5629R
Rights
open.access
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