Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006–2007

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.

Polarization Signatures of Relativistic Magnetohydrodynamic Shocks in the Blazar Emission Region. I. Force-Free Helical Magnetic Fields

“…Abdo et al (2010) have shown that at the end of a flare + PA swing event in 3C279, the PD rises up above the initial value, which is immediately followed by a significant restoration to approximately the initial PD level. The same restoring phases are seen in a number of flare + PA rotation events as well (Larionov et al 2008(Larionov et al , 2013Morozova et al 2014). On the other hand, in Case I the magnetization is too weak, thus the PD rises up to ∼70 % at the end of the flare and shows no restoration, indicating a purely poloidal magnetic structure.…”

“…This poses a tricky problem for slow shocks. On the other hand, for a relatively fast shock/disturbance, the polarization variations can either fluctuate around some mean value or smoothly rotate in the PA and present a restoring phase at the end of the flare; both are detected in observations (e.g., Larionov et al 2008;Abdo et al 2010;Blinov et al 2015). In summary, we prefer a strongly magnetized emission region, in which fast disturbances can be the driver of the flaring activities.…”

Analyzing polarization swings in 3C 279

“…5] magnetic field. In 3C 279 a 300 • counter-clockwise rotation of the optical EVPA was observed in 2006/2007 and explained by an emission feature on a spiral path in a helical magnetic field [6]. In 2009 a 210 • rotation in the opposite direction was observed and explained by a global bend of the jet [7].…”

MULTIWAVELENGTH STUDY OF QUIESCENT STATES OF Mrk 421 WITH UNPRECEDENTED HARD X-RAY COVERAGE PROVIDED BY NuSTAR IN 2013

“…The effective wavelength of this bandpass is not too different from the Kron-Cousins R band, and the wavelength dependence in the polarization of Mrk 421 seen in the spectropolarimetry during this period is not strong enough to significantly affect the variability analysis of the measurements from various telescopes. The observing and data-processing procedures for the polarization measurements are described in Larionov et al (2008), Smith et al (2009), andJorstad et al (2010).…”