Synchrotron flaring in the jet of 3C 279

¹ Tuorla Observatory, Väisälä Institute of Space Physics and Astronomy, University of Turku, 21500 Piikkiö, Finland e-mail: elilin@utu.fi
² Metsähovi Radio Observatory, Helsinki University of Technology, 02540 Kylmälä, Finland
³ Geneva Observatory, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
⁴ INTEGRAL Science Data Centre, Ch. d'Ecogia 16, 1290 Versoix, Switzerland
⁵ Department of Physics, University of Turku, 20100 Turku, Finland
⁶ Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
⁷ Max-Planck-Institut für Physik, München, Germany
⁸ INAF-Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁹ Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, College Lane, Herts, AL10 9AB, USA
¹⁰ Osservatorio Astronomico di Perugia, via Bonfigli, 06123 Perugia, Italy

Received: 22 June 2005
Accepted: 9 June 2006

Abstract

Aims.We study the synchrotron flaring behaviour of the blazar 3C 279 based on an extensive dataset covering 10 years of monitoring at 19 different frequencies in the radio-to-optical range.

Methods.The properties of a typical outburst are derived from the observations by decomposing the 19 lightcurves into a series of self-similar events. This analysis is achieved by fitting all data simultaneously to a succession of outbursts defined according to the shock-in-jet model of Marscher & Gear (1985).

Results.We compare the derived properties of the synchrotron outbursts in 3C 279 to those obtained with a similar method for the quasar 3C 273. It is argued that differences in the flaring behaviour of these two sources are intrinsic to the sources themselves rather than being due to orientation effects. We also compare the start times and flux densities of our modelled outbursts with those measured from radio components identified in Very Long Baseline Interferometry (VLBI) images. We find VLBI counterparts for most of our model outbursts, although some high-frequency peaking events are not seen in the radio maps. Finally, we study the link between the appearance of a new synchrotron component and the EGRET gamma-ray state of the source at 10 different epochs. We find that an early-stage shock component is always present during high gamma-ray states, while in low gamma-ray states the time since the onset of the last synchrotron outburst is significantly longer. This statistically significant correlation supports the idea that gamma-ray flares are associated with the early stages of shock components propagating in the jet. We note, however, that the shock wave is already beyond the broad line region during the gamma-ray flaring.