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A&A 453, 817-822 (2006)
DOI: 10.1051/0004-6361:20064817

The unprecedented optical outburst of the quasar 3C 454.3

The WEBT campaign of 2004-2005
M. Villata1, C. M. Raiteri1, T. J. Balonek2, M. F. Aller3, S. G. Jorstad4, O. M. Kurtanidze5, 6, 7, F. Nicastro8, 9, 10, K. Nilsson11, H. D. Aller3, A. Arai12, A. Arkharov13, U. Bach1, E. Benítez9, A. Berdyugin11, C. S. Buemi14, M. Böttcher15, D. Carosati16, R. Casas17, A. Caulet9, W. P. Chen18, P.-S. Chiang18, Y. Chou18, S. Ciprini11, 19, J. M. Coloma17, G. Di Rico20, C. Díaz21, N. V. Efimova13, 22, C. Forsyth2, A. Frasca14, L. Fuhrmann1, 19, B. Gadway2, S. Gupta15, V. A. Hagen-Thorn22, 23, J. Harvey15, J. Heidt7, H. Hernandez-Toledo9, F. Hroch24, C.-P. Hu18, R. Hudec25, M. A. Ibrahimov26, A. Imada27, M. Kamata12, T. Kato27, M. Katsuura12, T. Konstantinova22, E. Kopatskaya22, D. Kotaka12, Y. Y. Kovalev28, 29, Yu. A. Kovalev29, T. P. Krichbaum30, K. Kubota27, M. Kurosaki12, L. Lanteri1, V. M. Larionov22, 23, L. Larionova22, E. Laurikainen31, C.-U. Lee32, P. Leto33, A. Lähteenmäki34, O. López-Cruz35, E. Marilli14, A. P. Marscher4, I. M. McHardy36, S. Mondal18, B. Mullan2, N. Napoleone10, M. G. Nikolashvili5, J. M. Ohlert37, S. Postnikov15, T. Pursimo38, M. Ragni20, J. A. Ros17, K. Sadakane12, A. C. Sadun39, T. Savolainen11, E. A. Sergeeva40, L. A. Sigua5, A. Sillanpää11, L. Sixtova24, N. Sumitomo12, L. O. Takalo11, H. Teräsranta34, M. Tornikoski34, C. Trigilio14, G. Umana14, A. Volvach41, B. Voss42 and S. Wortel2

1  INAF, Osservatorio Astronomico di Torino, Italy
    e-mail: villata@to.astro.it
2  Foggy Bottom Observatory, Colgate University, NY, USA
3  Department of Astronomy, University of Michigan, MI, USA
4  Institute for Astrophysical Research, Boston University, MA, USA
5  Abastumani Astrophysical Observatory, Georgia
6  Astrophysikalisches Institut Potsdam, Germany
7  Landessternwarte Heidelberg-Königstuhl, Germany
8  Harvard-Smithsonian Center for Astrophysics, MA, USA
9  Instituto de Astronomía, UNAM, Mexico
10  INAF, Osservatorio Astronomico di Roma, Italy
11  Tuorla Observatory, Finland
12  Astronomical Institute, Osaka Kyoiku University, Japan
13  Main (Pulkovo) Astronomical Observatory of the Russian Academy of Sciences, Russia
14  INAF, Osservatorio Astrofisico di Catania, Italy
15  Astrophysical Institute, Department of Physics and Astronomy, Ohio University, OH, USA
16  Armenzano Astronomical Observatory, Italy
17  Agrupació Astronòmica de Sabadell, Spain
18  Institute of Astronomy, National Central University, Taiwan
19  Dipartimento di Fisica e Osservatorio Astronomico, Università di Perugia, Italy
20  INAF, Osservatorio Astronomico di Teramo, Italy
21  Departamento de Astrofísica, Universidad Complutense, Spain
22  Astronomical Institute, St.-Petersburg State University, Russia
23  Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia
24  Institute of Theoretical Physics and Astrophysics, Masaryk University, Czech Republic
25  Astronomical Institute, Academy of Sciences of the Czech Republic, Czech Republic
26  Ulugh Beg Astronomical Institute, Academy of Sciences of Uzbekistan, Uzbekistan
27  Department of Astronomy, Kyoto University, Japan
28  Jansky fellow, National Radio Astronomy Observatory, WV, USA
29  Astro Space Center of Lebedev Physical Institute, Russia
30  Max-Planck-Institut für Radioastronomie, Germany
31  Division of Astronomy, University of Oulu, Finland
32  Korea Astronomy and Space Science Institute, South Korea
33  INAF, Istituto di Radioastronomia Sezione di Noto, Italy
34  Metsähovi Radio Observatory, Helsinki University of Technology, Finland
35  Instituto Nacional de Astrofísica, Optica y Electrónica (INAOE), Mexico
36  School of Physics and Astronomy, The University, UK
37  Michael Adrian Observatory, Germany
38  Nordic Optical Telescope, Roque de los Muchachos Astronomical Observatory, TF, Spain
39  Department of Physics, University of Colorado at Denver and Health Sciences Center, CO, USA
40  Crimean Astrophysical Observatory, Ukraine
41  Radio Astronomy Laboratory of Crimean Astrophysical Observatory, Ukraine
42  Institut für Theoretische Physik und Astrophysik der Universität Kiel, Germany

(Received 31 January 2006 / Accepted 2 March 2006)

Abstract
Context.The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was R=12.0, which represents the most luminous quasar state thus far observed ( $M_B \sim -31.4$).
Aims.In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT).
Methods.Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005.
Results.The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm the brightening of the radio core and show an increasing polarization. An exceptionally bright X-ray state was detected in May 2005, corresponding to the rising mm flux and suggesting an inverse-Compton nature of the hard X-ray spectrum.
Conclusions.A further multifrequency monitoring effort is needed to follow the next phases of this unprecedented event.


Key words: galaxies: active -- galaxies: quasars: general -- galaxies: quasars: individual: 3C 454.3 -- galaxies: jets



© ESO 2006


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