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

Abstract

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.