A Multi-Wavelength Polarimetric Study of the Blazar Cta 102 During a Gamma-Ray Flare in 2012

Abstract

We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright γ-ray outburst detected by the Fermi Large Area Telescope in September-October 2012 when the source reached a flux of F >100 MeV = 5.2 ± 0.4 × 10 −6 photons cm −2 s −1 . At the same time the source displayed an unprecedented optical and NIR outburst. We study the evolution of the parsecscale jet with ultra-high angular resolution through a sequence of 80 total and polarized intensity Very Long Baseline Array images at 43 GHz, covering the observing period from June 2007 to June 2014. We find that the γ-ray outburst is coincident with flares at all the other frequencies and is related to the passage of a new superluminal knot through the radio core. The powerful γ-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight (θ ∼1.2 • ) during the ejection of the knot and the γ-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of EVPAs, which we associate with the path followed by the knot as it moves along helical magnetic field lines, although a random walk of the EVPA caused by a turbulent magnetic field cannot be ruled out. We locate the γ-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of near-infrared to ultraviolet photons is the probable mechanism for the γ-ray production.

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

“…Tabulated data correspond to flux density, distance and position angle from the core, and size. Errors in the model-fit parameters for each component are estimated based on its brightness temperature following Casadio et al (2015).…”

The Connection between the Radio Jet and the γ-ray Emission in the Radio Galaxy 3C 120 and the Blazar CTA 102

“…In both cases we considered a successful detection when the test statistic TS was greater than 10, which corresponds to a signal-to-noise ratio >3σ; when TS < 10 a 2σ upper limit of the flux is provided. For further details on the γ-ray analysis of both sources see [7,8].…”

“…A more detailed description of the multi-wavelength dataset and the calibration procedures is reported in [7,8].…”

“…The analysis of the entire dataset for both 3C 120 and CTA 102 and the results obtained in both studies have been recently reported in [7,8], respectively. Here we describe the main results achieved focusing the attention on the common properties displayed by these two sources during the high-energy events, despite belonging to two different classes of AGN.…”

The Power of (Near) Simultaneous Multi-Frequency Observations for mm-VLBI and Astrometry

“…Results from the VLBA-BU-BLAZAR program, show that most γ-ray flares are simultaneous within errors with the appearance of a new superluminal component or a major outburst in the core of the jet, which is defined as the bright, compact feature in the upstream end of the jet [10][11][12]. A burst in particle and magnetic energy density is therefore required when jet disturbances cross the radio core in order to produce γ-ray flares, which can naturally be explained by identifying the radio core with a recollimation shock [13][14][15].…”