RAITERI, Claudia MariaClaudia MariaRAITERIVILLATA, MassimoMassimoVILLATALarionov, V MV MLarionovJorstad, S GS GJorstadMarscher, A PA PMarscherWeaver, Z RZ RWeaverAcosta-Pulido, J AJ AAcosta-PulidoAgudo, IIAgudoAndreeva, TTAndreevaArkharov, AAArkharovBachev, RRBachevBenítez, EEBenítezBerton, MMBertonBjörklund, IIBjörklundBorman, G AG ABormanBozhilov, VVBozhilovCARNERERO MARTIN, Maria IsabelMaria IsabelCARNERERO MARTINCarosati, DDCarosatiCasadio, CCCasadioChen, W PW PChenDamljanovic, GGDamljanovicD'AMMANDO, FILIPPOFILIPPOD'AMMANDOEscudero, JJEscuderoFuentes, AAFuentesGIROLETTI, MARCELLOMARCELLOGIROLETTIGrishina, T ST SGrishinaGupta, A CA CGuptaHagen-Thorn, V AV AHagen-ThornHart, MMHartHiriart, DDHiriartHou, W-JW-JHouIvanov, DDIvanovKim, J-YJ-YKimKimeridze, G NG NKimeridzeKonstantopoulou, CCKonstantopoulouKopatskaya, E NE NKopatskayaKurtanidze, O MO MKurtanidzeKurtanidze, S OS OKurtanidzeLähteenmäki, AALähteenmäkiLarionova, E GE GLarionovaLarionova, L VL VLarionovaMARCHILI, NicolaNicolaMARCHILIMarkovic, GGMarkovicMinev, MMMinevMorozova, D AD AMorozovaMyserlis, IIMyserlisNakamura, MMNakamuraNikiforova, A AA ANikiforovaNikolashvili, M GM GNikolashviliOtero-Santos, JJOtero-SantosOvcharov, EEOvcharovPursimo, TTPursimoRahimov, IIRahimovRIGHINI, SIMONASIMONARIGHINISakamoto, TTSakamotoSavchenko, S SS SSavchenkoSemkov, E HE HSemkovShakhovskoy, DDShakhovskoySigua, L AL ASiguaStojanovic, MMStojanovicStrigachev, AAStrigachevThum, CCThumTornikoski, MMTornikoskiTraianou, EETraianouTroitskaya, Y VY VTroitskayaTroitskiy, I SI STroitskiyTsai, AATsaiValcheva, AAValchevaVasilyev, A AA AVasilyevVince, OOVinceZaharieva, EEZaharieva2022-03-222022-03-2220210035-8711http://hdl.handle.net/20.500.12386/31777Among 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.STAMPAenArticle10.1093/mnras/stab12682-s2.0-85108587265https://academic.oup.com/mnras/article/504/4/5629/6270904?login=truehttp://arxiv.org/abs/2104.15005v12021MNRAS.504.5629RFIS/05 - ASTRONOMIA E ASTROFISICA