The complex variability of blazars: time-scales and periodicity analysis in S4 0954+65

DOI: 
10.1093/mnras/stab1268
Publication date: 
24/07/2021
Main author: 
Raiteri, C. M.
IAA authors: 
Agudo, I.;Escudero, J.;Fuentes, A.
Authors: 
Raiteri, C. M.;Villata, M.;Larionov, V. M.;Jorstad, S. G.;Marscher, A. P.;Weaver, Z. R.;Acosta-Pulido, J. A.;Agudo, I.;Andreeva, T.;Arkharov, A.;Bachev, R.;Benítez, E.;Berton, M.;Björklund, I.;Borman, G. A.;Bozhilov, V.;Carnerero, M. I.;Carosati, D.;Casadio, C.;Chen, W. P.;Damljanovic, G.;D'Ammando, F.;Escudero, J.;Fuentes, A.;Giroletti, M.;Grishina, T. S.;Gupta, A. C.;Hagen-Thorn, V. A.;Hart, M.;Hiriart, D.;Hou, W. -J.;Ivanov, D.;Kim, J. -Y.;Kimeridze, G. N.;Konstantopoulou, C.;Kopatskaya, E. N.;Kurtanidze, O. M.;Kurtanidze, S. O.;Lähteenmäki, A.;Larionova, E. G.;Larionova, L. V.;Marchili, N.;Markovic, G.;Minev, M.;Morozova, D. A.;Myserlis, I.;Nakamura, M.;Nikiforova, A. A.;Nikolashvili, M. G.;Otero-Santos, J.;Ovcharov, E.;Pursimo, T.;Rahimov, I.;Righini, S.;Sakamoto, T.;Savchenko, S. S.;Semkov, E. H.;Shakhovskoy, D.;Sigua, L. A.;Stojanovic, M.;Strigachev, A.;Thum, C.;Tornikoski, M.;Traianou, E.;Troitskaya, Y. V.;Troitskiy, I. S.;Tsai, A.;Valcheva, A.;Vasilyev, A. A.;Vince, O.;Zaharieva, E.
Journal: 
Monthly Notices of the Royal Astronomical Society
Publication type: 
Article
Volume: 
504
Pages: 
5629
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.
Database: 
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2021MNRAS.504.5629R/abstract
ADS Bibcode: 
2021MNRAS.504.5629R
Keywords: 
galaxies: active;BL Lacertae objects: general;BL Lacertae objects: individual: S4 0954+65;galaxies: jets;Astrophysics - High Energy Astrophysical Phenomena;Astrophysics - Astrophysics of Galaxies