Volume 492, Number 2, December III 2008
|Page(s)||389 - 400|
|Published online||27 October 2008|
Astron. Inst., St.-Petersburg State Univ., Russia e-mail: email@example.com
2 Pulkovo Observatory, St.-Petersburg, Russia
3 Inst. for Astrophys. Research, Boston Univ., MA, USA
4 INAF, Osservatorio Astronomico di Torino, Italy
5 Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain
6 Department of Astronomy, University of Michigan, MI, USA
7 Ulugh Beg Astron. Inst., Tashkent, Uzbekistan
8 Max-Planck-Institut für Radioastronomie, Bonn, Germany
9 Inst. of Astron., Bulgarian Acad. of Sciences, Sofia, Bulgaria
10 Tuorla Observatory, Univ. of Turku, Piikkiö, Finland
11 Department of Physics and Astronomy, Ohio Univ., OH, USA
12 INAF, Osservatorio Astrofisico di Catania, Italy
13 Oss. Astronomico della Regione Autonoma Valle d'Aosta, Italy
14 Armenzano Astronomical Observatory, Italy
15 Lab. d'Astrophys., Univ. Bordeaux 1, CNRS, Floirac, France
16 Institute of Astronomy, National Central University, Taiwan
17 INAF, Osservatorio Astronomico di Roma, Italy
18 INAF, Osservatorio Astronomico di Collurania Teramo, Italy
19 COMU Observatory, Turkey
20 Crimean Astrophysical Observatory, Ukraine
21 Moscow Univ., Crimean Lab. of Sternberg Astron. Inst., Ukraine
22 Isaac Newton Institute of Chile, Crimean Branch, Ukraine
23 ASI Science Data Centre, Frascati, Italy
24 Department of Phys. and Astron. Univ. of Aarhus, Denmark
25 YNAO, Chinese Academy of Sciences, Kunming, PR China
26 ARIES, Manora Peak, Nainital, India
27 Harvard-Smithsonian Center for Astroph., Cambridge, MA, USA
28 Astronomical Institute, Osaka Kyoiku University, Japan
29 Astro Space Centre of Lebedev Physical Inst., Moscow, Russia
30 Abastumani Astrophysical Observatory, Georgia
31 Metsähovi Radio Obs., Helsinki Univ. of Technology, Finland
32 INAF, Istituto di Radioastronomia, Sezione di Noto, Italy
33 Korea Astronomy and Space Science Institute, South Korea
34 University of Southampton, UK
35 Special Astrophysical Observatory, N. Arkhyz, Russia
36 Michael Adrian Observatory, Trebur, Germany
37 Cardiff University, Wales, UK
38 Nordic Optical Telescope, Santa Cruz de La Palma, Spain
39 Agrupació Astronòmica de Sabadell, Spain
40 Dept. of Phys., Univ. of Colorado, Denver, USA
41 Cork Institute of Technology, Cork, Ireland
42 Instituto de Radioastronomía Milimétrica, Granada, Spain
43 Radio Astron. Lab. of Crimean Astroph. Observatory, Ukraine
Accepted: 17 October 2008
Context. The quasar 3C 279 is among the most extreme blazars in terms of luminosity and variability of flux at all wavebands. Its variations in flux and polarization are quite complex and therefore require intensive monitoring observations at multiple wavebands to characterise and interpret the observed changes.
Aims. In this paper, we present radio-to-optical data taken by the WEBT, supplemented by our VLBA and RXTE observations, of 3C 279. Our goal is to use this extensive database to draw inferences regarding the physics of the relativistic jet.
Methods. We assemble multifrequency light curves with data from 30 ground-based observatories and the space-based instruments SWIFT (UVOT) and RXTE, along with linear polarization vs. time in the optical R band. In addition, we present a sequence of 22 images (with polarization vectors) at 43 GHz at resolution 0.15 milliarcsec, obtained with the VLBA. We analyse the light curves and polarization, as well as the spectral energy distributions at different epochs, corresponding to different brightness states.
Results. We find that the IR-optical-UV continuum spectrum of the variable component corresponds to a power law with a constant slope of -1.6, while in the 2.4–10 keV X-ray band it varies in slope from -1.1 to -1.6. The steepest X-ray spectrum occurs at a flux minimum. During a decline in flux from maximum in late 2006, the optical and 43 GHz core polarization vectors rotate by ~300°.
Conclusions. The continuum spectrum agrees with steady injection of relativistic electrons with a power-law energy distribution of slope -3.2 that is steepened to -4.2 at high energies by radiative losses. The X-ray emission at flux minimum comes most likely from a new component that starts in an upstream section of the jet where inverse Compton scattering of seed photons from outside the jet is important. The rotation of the polarization vector implies that the jet contains a helical magnetic field that extends ~20 pc past the 43 GHz core.
Key words: galaxies: active / quasars: general / quasars: individual: 3C 279
© ESO, 2008
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