Catching the radio flare in CTA 102: II. VLBI kinematic analysis

TL;DR

This study uses VLBI observations of CTA 102 during its 2006 radio flare to analyze jet kinematics, identify potential shocks, and connect these features to the flare's evolution, providing insights into blazar jet physics.

Contribution

It presents the first detailed multifrequency VLBI kinematic analysis of CTA 102 during a major flare, identifying recollimation shocks and linking jet features to the flare activity.

Findings

Identification of two recollimation shocks at 0.1 mas and 6.0 mas from the core.

Detection of a jet feature ejected during the flare, possibly involved in shock-shock interaction.

Evidence linking jet features to the observed radio flare and double peak structure.

Abstract

We performed multifrequency multiepoch Very Long Baseline Array (VLBA) observations of the blazar CTA 102 during its 2006 radio flare, the strongest ever reported for this source. These observations provide an excellent opportunity to investigate the evolution of the physical properties of blazars, especially during these flaring events. We want to study the kinematic changes in the source during the strong radio outburst in April 2006 and test the assumption of a shock-shock interaction. This assumption is based on the analysis and modeling of the single-dish observations of CTA\,102 (Paper I). In this paper we study the kinematics of CTA 102 at several frequencies using VLBI observations. From the modeled jet features we derived estimates for the evolution of the physical parameters, such as the particle density and the magnetic field. Furthermore, we combined our observations during the 2006 flare with long-term VLBA monitoring of the source at 15 GHz and 43 GHz. We cross-identified seven features throughout our entire multifrequency observations and find evidence of two possible recollimation shocks around 0.1 mas (deprojected 18 pc at a viewing angle of 2.6 degrees) and 6.0 mas (deprojected 1 kpc) from the core. The 43 GHz observations reveal a feature ejected at epoch $t_\mathrm{ej}=2005.9\pm0.2$, which could be connected to the 2006 April radio flare. Furthermore, this feature might be associated with the traveling component involved in the possible shock-shock interaction, which gives rise to the observed double peak structure in the single-dish light curves reported in Paper I.