A&A 464, L5-L9 (2007)
DOI: 10.1051/0004-6361:20066958

Letter

The radio delay of the exceptional 3C 454.3 outburst

Follow-up WEBT observations in 2005-2006

M. Villata¹, C. M. Raiteri¹, M. F. Aller², U. Bach^{1, 3}, M. A. Ibrahimov⁴, Y. Y. Kovalev^{3, 5, 6}, O. M. Kurtanidze^{7, 8, 9}, V. M. Larionov^{10, 11}, C.-U. Lee¹², P. Leto¹³, A. Lähteenmäki¹⁴, K. Nilsson¹⁵, T. Pursimo¹⁶, J. A. Ros¹⁷, N. Sumitomo¹⁸, A. Volvach¹⁹, H. D. Aller², A. Arai¹⁸, C. S. Buemi²⁰, J. M. Coloma¹⁷, V. T. Doroshenko²¹, Yu. S. Efimov²², L. Fuhrmann^{1, 23, 3}, V. A. Hagen-Thorn^{10, 11}, M. Kamada¹⁸, M. Katsuura¹⁸, T. Konstantinova¹⁰, E. Kopatskaya¹⁰, D. Kotaka¹⁸, Yu. A. Kovalev⁵, M. Kurosaki¹⁸, L. Lanteri¹, L. Larionova¹⁰, M. G. Mingaliev²⁴, S. Mizoguchi¹⁸, K. Nakamura¹⁸, M. G. Nikolashvili⁷, S. Nishiyama¹⁸, K. Sadakane¹⁸, S. G. Sergeev²², L. A. Sigua⁷, A. Sillanpää¹⁵, R. L. Smart¹, L. O. Takalo¹⁵, K. Tanaka¹⁸, M. Tornikoski¹⁴, C. Trigilio²⁰, and G. Umana<sup>20

1</sup>  INAF, Osservatorio Astronomico di Torino, Italy
    e-mail: villata@oato.inaf.it
²  Department of Astronomy, University of Michigan, MI, USA
³  Max-Planck-Institut für Radioastronomie, Germany
⁴  Ulugh Beg Astronomical Institute, Academy of Sciences of Uzbekistan, Uzbekistan
⁵  Astro Space Center of Lebedev Physical Institute, Russia
⁶  National Radio Astronomy Observatory, Green Bank, WV, USA
⁷  Abastumani Astrophysical Observatory, Georgia
⁸  Astrophysikalisches Institut Potsdam, Germany
⁹  Landessternwarte Heidelberg-Königstuhl, Germany
¹⁰  Astronomical Institute, St.-Petersburg State University, Russia
¹¹  Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia
¹²  Korea Astronomy and Space Science Institute, South Korea
¹³  INAF, Istituto di Radioastronomia Sezione di Noto, Italy
¹⁴  Metsähovi Radio Observatory, Helsinki University of Technology, Finland
¹⁵  Tuorla Observatory, Finland
¹⁶  Nordic Optical Telescope, Roque de los Muchachos Astronomical Observatory, TF, Spain
¹⁷  Agrupació Astronòmica de Sabadell, Spain
¹⁸  Astronomical Institute, Osaka Kyoiku University, Japan
¹⁹  Radio Astronomy Laboratory of Crimean Astrophysical Observatory, Ukraine
²⁰  INAF, Osservatorio Astrofisico di Catania, Italy
²¹  Moscow State University, Russia
²²  Crimean Astrophysical Observatory (CrAO), Ukraine
²³  Dipartimento di Fisica e Osservatorio Astronomico, Università di Perugia, Italy
²⁴  Special Astrophysical Observatory, Russia

(Received 18 December 2006 / Accepted 28 December 2006)

Abstract
Context.In spring 2005 the blazar 3C 454.3 was observed in an unprecedented bright state from the near-IR to the hard X-ray frequencies. A mm outburst peaked in June-July 2005, and it was followed by a flux increase at high radio frequencies.
Aims.In this paper we report on multifrequency monitoring by the WEBT aimed at following the further evolution of the outburst in detail. In particular, we investigate the expected correlation and time delays between the optical and radio emissions in order to derive information on the variability mechanisms and jet structure.
Methods.A comparison among the light curves at different frequencies is performed by means of visual inspection and discrete correlation function, and the results are interpreted with a simple model taking into account Doppler factor variations of geometric origin.
Results.The high-frequency radio light curves show a huge outburst starting during the dimming phase of the optical one and lasting more than 1 year. The first phase is characterized by a slow flux increase, while in early 2006 a major flare is observed. The lower-frequency radio light curves show a progressively delayed and fainter event, which disappears below 8 GHz. We suggest that the radio major peak is not physically connected with the spring 2005 optical one, but it is actually correlated with a minor optical flare observed in October-November 2005. This interpretation involves both an intrinsic and a geometric mechanism. The former is represented by disturbances travelling down the emitting jet, the latter being due to the curved-jet motion, with the consequent differential changes of viewing angles of the different emitting regions.

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

© ESO 2007

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.