Raiteri, C. M.Villata, M.Aller, M. F.Gurwell, M. A.Kurtanidze, O. M.Lähteenmäki, A.Larionov, V. M.Romano, P.Vercellone, S.Agudo, I.Aller, H. D.Arkharov, A. A.Bach, U.Benítez, E.Berdyugin, A.Blinov, D. A.Borisova, E. V.Böttcher, M.Bravo Calle, O. J.A.Buemi, C. S.Calcidese, P.Carosati, D.Casas, R.Chen, W. P.Efimova, N. V.Gómez, J. L.Gusbar, C.Hawkins, K.Heidt, J.Hiriart, D.Hsiao, H. Y.Jordan, B.Jorstad, S. G.Joshi, M.Kimeridze, G. N.Koptelova, E.Konstantinova, T. S.Kopatskaya, E. N.Kurtanidze, S. O.Larionova, E. G.Larionova, L. V.Leto, P.Li, Y.Ligustri, R.Lindfors, E.Lister, M.Marscher, A. P.Molina, S. N.Morozova, D. A.Nieppola, E.Nikolashvili, M. G.Nilsson, K.Palma, N.Pasanen, M.Reinthal, R.Roberts, V.Ros, J. A.Roustazadeh, P.Sadun, A. C.Sakamoto, T.Schwartz, R. D.Sigua, L. A.Sillanpää, A.Takalo, L. O.Tammi, J.Taylor, B.Tornikoski, M.Trigilio, C.Troitsky, I. S.Umana, G.Volvach, A.Yuldasheva, T. A.2025-12-162025-12-160004-6361ORCID:/0000-0003-2886-9341/work/171152007https://hdl.handle.net/1885/733795175Context. The blazar 3C 454.3 is one of the most active sources from the radio to the γ-ray frequencies observed in the past few years. Aims. We present multiwavelength observations of this source from April 2008 to March 2010. The radio to optical data are mostly from the GASP-WEBT, UV and X-ray data from Swift, and γ-ray data from the AGILE and Fermi satellites. The aim is to understand the connection among emissions at different frequencies and to derive information on the emitting jet. Methods. Light curves in 18 bands were carefully assembled to study flux variability correlations. We improved the calibration of optical-UV data from the UVOT and OM instruments and estimated the Lyα flux to disentangle the contributions from different components in this spectral region. Results. The observations reveal prominent variability above 8 GHz. In the optical-UV band, the variability amplitude decreases with increasing frequency due to a steadier radiation from both a broad line region and an accretion disc. The optical flux reaches nearly the same levels in the 2008-2009 and 2009-2010 observing seasons; the mm one shows similar behaviour, whereas the γ and X-ray flux levels rise in the second period. Two prominent γ-ray flares in mid 2008 and late 2009 show a double-peaked structure, with a variable γ/optical flux ratio. The X-ray flux variations seem to follow the γ-ray and optical ones by about 0.5 and 1 d, respectively. Conclusions. We interpret the multifrequency behaviour in terms of an inhomogeneous curved jet, where synchrotron radiation of increasing wavelength is produced in progressively outer and wider jet regions, which can change their orientation in time. In particular, we assume that the long-term variability is due to this geometrical effect. By combining the optical and mm light curves to fit the γ and X-ray ones, we find that the γ (X-ray) emission may be explained by inverse-Comptonisation of synchrotron optical (IR) photons by their parent relativistic electrons (SSC process). A slight, variable misalignment between the synchrotron and Comptonisation zones would explain the increased γ and X-ray flux levels in 2009-2010, as well as the change in the γ/optical flux ratio during the outbursts peaks. The time delays of the X-ray flux changes after the γ, and optical ones are consistent with the proposed scenario.C.M.R. is grateful to Stefania Rasetti from the Torino Observatory Computer Centre for her assistance. We thank the Fermi-LAT team for providing Fermi data. We acknowledge the use of public data from the Swift data archive. We acknowledge financial contribution from the agreement ASI-INAF I/009/10/0. St.-Petersburg University team acknowledges support from Russian RFBR foundation via grant 09-02-00092. Abastumani Observatory team acknowledges financial support by the Georgian National Science Foundation through grant GNSF/ST08/4-404. The Metsähovi team acknowledges the support from the Academy of Finland to our observing projects (numbers 212656, 210338, 121148, and others). The University of Michigan team acknowledges financial support through the NASA Fermi grants NNX09AU16G, NNX10AP16G, and NSF grant AST-0607523. The operation of UMRAO is funded by the University of Michigan. This paper is partly based on observations carried out at the German-Spanish Calar Alto Observatory, which is jointly operated by the MPIA and the IAA-CSIC. Acquisition of the MAPCAT data is supported in part by MICIIN (Spain) grant and AYA2010-14844, and by CEIC (Andalucía) grant P09-FQM-4784. Partly based on observations with the Medicina and Noto telescopes operated by INAF – Istituto di Radioastronomia. This research has made use of NASA’s Astrophysics Data System and of the XRT Data Analysis Software (XRTDAS) developed under the responsibility of the ASI Science Data Center (ASDC), Italy. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009). The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The research at Boston U. was supported by NSF grant AST-0907893 and NASA Fermi GI grants NNX08AV65G, NNX08AV61G, and NNX09AT99G. The PRISM camera at Lowell Observatory was developed by K. Janes et al. at BU and Lowell Observatory, with funding from the NSF, BU, and Lowell Observatory.engalaxies: activegalaxies: jetsquasars: generalquasars: individual: 3C 454.3201110.1051/0004-6361/20111702680053997339