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

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.

Description

Funding Information: This research has made use of NASA's Astrophysics Data System and of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The research at Boston University was supported by NASA grants 80NSSC20K1566 (Fermi Guest Investigator Program) and 80NSSC21K0243 (TESS Guest Investigator Program). This studywas based (in part) on observations conducted using the 1.8 m Perkins Telescope Observatory (PTO) in Arizona (USA), which is owned and operated by Boston University. GD, MS, GM, and OV acknowledge the observing grant support from the Institute of Astronomy and Rozhen NAO BAS through the bilateral joint research project 'Gaia Celestial Reference Frame (CRF) and fast variable astronomical objects' (2020-2022, leader is G.Damljanovic), and support by the Ministry of Education, Science and Technological Development of the Republic of Serbia (contract No451-03-68/2020-14/200002) This researchwas partially supported by the Bulgarian National Science Fund of the Ministry of Education and Science under grants DN 18-13/2017, KP-06- H28/3 (2018), KP-06-H38/4 (2019), and KP-06-KITAJ/2 (2020). SOK acknowledges financial support by Shota Rustaveli National Science Foundation of Georgia under contract PHDF-18-354 EB acknowledges support from DGAPA-PAPIIT GRANT IN113320. This work is partly based upon observations carried out at the Observatorio Astronomico Nacional on the Sierra San Pedro Martir (OAN- SPM), Baja California, Mexico. We acknowledge support by Bulgarian National Science Fund under grant DN18-10/2017 and National RI Roadmap Project DO1-383/18.12.2020 of the Ministry of Education and Science of the Republic of Bulgaria. IA acknowledges financial support from the Spanish 'Ministerio de Ciencia e Innovacion' (MCINN) through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofisica de Andalucia-CSIC (SEV-2017-0709). Acquisition and reduction of the POLAMI data was supported in part by MICINN through grants AYA2016- 80889-P and PID2019-107847RB-C44. The POLAMI observations were carried out at the IRAM 30m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain) Publisher Copyright: © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.

Keywords

BL Lacertae objects: general, BL Lacertae objects: individual: S4 0954+65, Galaxies: active, Galaxies: jets

DOI

10.1093/mnras/stab1268

Citation

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 , YV , Troitskiy , I S , Tsai , A , Valcheva , A , Vasilyev , A A , Vince , O & Zaharieva , E 2021 , ' The complex variability of blazars: Time-scales and periodicity analysis in S4 0954+65 ' , Monthly Notices of the Royal Astronomical Society , vol. 504 , no. 4 , pp. 5629-5646 . https://doi.org/10.1093/mnras/stab1268

Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-202108048148

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[article-cris] Sähkötekniikan korkeakoulu / ELEC

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