MAGIC observations and multifrequency properties of the flat spectrum radio quasar 3C 279 in 2011

Abstract

Aims. We study the multifrequency emission and spectral properties of the quasar 3C 279 aimed at identifying the radiation processes taking place in the source. Methods. We observed 3C 279 in very-high-energy (VHE, E > 100 GeV) γ-rays, with the MAGIC telescopes during 2011, for the first time in stereoscopic mode. We combined these measurements with observations at other energy bands: in high-energy (HE, E > 100 MeV) γ-rays from Fermi-LAT; in X-rays from RXTE; in the optical from the KVA telescope; and in the radio at 43 GHz, 37 GHz, and 15 GHz from the VLBA, Metsähovi, and OVRO radio telescopes -along with optical polarisation measurements from the KVA and Liverpool telescopes. We examined the corresponding light curves and broadband spectral energy distribution and we compared the multifrequency properties of 3C 279 at the epoch of the MAGIC observations with those inferred from historical observations. Results. During the MAGIC observations (2011 February 8 to April 11) 3C 279 was in a low state in optical, X-ray, and γ-rays. The MAGIC observations did not yield a significant detection. The derived upper limits are in agreement with the extrapolation of the HE γ-ray spectrum, corrected for EBL absorption, from Fermi-LAT. The second part of the MAGIC observations in 2011 was triggered by a high-activity state in the optical and γ-ray bands. During the optical outburst the optical electric vector position angle (EVPA) showed a rotation of ∼180• . Unlike previous cases, there was no simultaneous rotation of the 43 GHz radio polarisation angle. No VHE γ-rays were detected by MAGIC, and the derived upper limits suggest the presence of a spectral break or curvature between the Fermi-LAT and MAGIC bands. The combined upper limits are the strongest derived to date for the source at VHE and below the level of the previously detected flux by a factor of ∼2. Radiation models that include synchrotron and inverse Compton emissions match the optical to γ-ray data, assuming an emission component inside the broad line region with size R = 1.1 × 10 16 cm and magnetic field B = 1.45 G responsible for the high-energy emission, and another one outside the broad line region and the infrared torus (R = 1.5 × 10 17 cm and B = 0.8 G) causing the optical and low-energy emission. We also study the optical polarisation in detail and interpret it with a bent trajectory model.

Optical Polarimetric and Multiwavelength Flaring Activity of Blazar 3C 279

“…The full set of parameters derived by using our model are: Doppler factor δ D = 14 -18, magnetic field B = (0.14 − 2.5) G, emitting radius r d = (1.1 -2.1) ×10 17 cm and electron density N e =(0.1 -0.26) × 10 3 cm −3 with different values of power indexes between 1 and 6.1. The values reported in our model agree with those found by Paliya et al (2015); Hayashida et al (2015Hayashida et al ( , 2012; Aleksić et al (2014). Our best models allowed to estimate that variability timescales are in the range of 3.3 to 4.0 days.…”

“…A shock compression of an ordered helical magnetic field in an axisymmetric jet model (Zhang et al 2015) and the bent jet model (Nalewajko 2010) were proposed to interpret this atypical correlations. Similarly, the bent jet model was required to explain the EVPA variations presented in the multi-wavelength campaign in 2011 (Aleksić et al 2014). In addition, Larionov et al (2008) presented a multiwavelength study based on the X-ray, optical and radio bands and polarimetric observations collected during 2006-2007. They reported large EVPA variations which were explained by a large-scale helical magnetic field moving through the jet .…”

Multiwavelength analysis of brightness variations of 3C 279: probing the relativistic jet structure and its evolution

“…Because of the sin 2PA and cos 2PA dependence of the Stokes parameters, a continuous and gradual rotation in PA will appear as consecutive quadrant changes in that plane. In 2010, we detected a slow and gradual rotation of about 100 o over six months and, although there are gaps that prevent an unambiguous determination of the direction of rotation, this behavior was also observed by Aleksić et al (2014) and by Kiehlmann et al (2016).…”

Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

“…Figure2.23 shows the evolution of Θ of C31 as it curved toward the normal direction of the jet with increased separation from the core. Note that C31 might be associated with the knot A1 discussed by Aleksić et al (2014a), although additional epochs suggest a later time of ejection of C31 than that of A1. On the other hand, the uncertainty in T • is significant because the distance of the knot in 2011 with respect to the core changed only from 0.1 to 0.2mas, while its P.A.…”

“…We propose two possible explanations of the strong flare in C31 several parsecs from the core: (1) C31 crossed the line of sight, maximizing its Doppler beaming factor, in the summer of 2012; this is supported by a very slow speed of the knot in the first half of 2012 and rapid acceleration afterward (Figure4.23, left); and (2) in the summer of 2012, C31 interacts with the second brightest moving feature in the jet, C32, which was ejected earlier but moves more slowly than C31. Knot C32 can be associated with feature A2 discussed in Aleksić et al (2014a).…”