Volume 534, October 2011
|Number of page(s)||16|
|Published online||10 October 2011|
The long-lasting activity of 3C 454.3
INAF, Osservatorio Astronomico di Torino, Italy
2 Department of Astronomy, University of Michigan, MI, USA
3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
4 Abastumani Observatory, Mt. Kanobili, Abastumani, Georgia
5 Aalto University Metsähovi Radio Observatory, Kylmälä, Finland
6 Astron. Inst., St.-Petersburg State Univ., Russia
7 Pulkovo Observatory, St.-Petersburg, Russia
8 Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia
9 INAF-IASF Palermo, Italy
10 Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain
11 Institute for Astrophysical Research, Boston University, MA, USA
12 Max-Planck-Institut für Radioastronomie, Bonn, Germany
13 Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico
14 Tuorla Observatory, Univ. of Turku, Piikkiö, Finland
15 Astrophysical Inst., Department of Physics and Astronomy, Ohio Univ., Athens OH, USA
16 INAF, Osservatorio Astrofisico di Catania, Italy
17 Osservatorio Astronomico della Regione Autonoma Valle d’ Aosta, Italy
18 EPT Observatories, Tijarafe, La Palma, Spain
19 INAF, TNG Fundación Galileo Galilei, La Palma, Spain
20 Institut de Ciències de l’Espai (CSIC-IEEC), Spain
21 Agrupació Astronòmica de Sabadell, Spain
22 GraduateInstitute of Astronomy, National Central University, Taiwan
23 ZAH, Landessternwarte Heidelberg-Königstuhl, Germany
24 Lulin Observatory, National Central University, Taiwan
25 School of Cosmic Physics, Dublin Institute For Advanced Studies, Ireland
26 Department of Physics, National Taiwan University, Taipei, Taiwan
27 Circolo Astrofili Talmassons, Italy
28 Department of Physics, Purdue University, West Lafayette, IN, USA
29 Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Piikkiö, Finland
30 Facultad de Ciencias Espaciales, Univ. Nacional Autonoma de Honduras, Tegucigalpa M.D.C., Honduras
31 Department of Physics, Univ. of Colorado Denver, CO, USA
32 Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD, USA
33 Galaxy View Observatory, Sequim, Washington, USA
34 Lowell Observatory, Flagstaff, AZ, USA
35 Radio Astronomy Laboratory of Crimean Astrophysical Observatory, Ukraine
Received: 5 April 2011
Accepted: 24 June 2011
Context. 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.
Key words: galaxies: active / quasars: general / quasars: individual: 3C 454.3 / galaxies: jets
© ESO, 2011
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