Issue |
A&A
Volume 492, Number 2, December III 2008
|
|
---|---|---|
Page(s) | 389 - 400 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:200810937 | |
Published online | 27 October 2008 |
Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006–2007*
1
Astron. Inst., St.-Petersburg State Univ., Russia e-mail: vlar@astro.spbu.ru
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
Received:
8
September
2008
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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