Core-shift and spectral analysis of the 2006 radio flare in CTA102

TL;DR

This paper investigates the 2006 radio flare in CTA102, analyzing multi-frequency VLBI data to understand jet dynamics, core-shift behavior, and shock interactions, revealing an over-pressured jet influenced by traveling shocks.

Contribution

It provides a detailed core-shift and spectral analysis during a major flare, highlighting deviations from typical models and supporting a shock interaction scenario.

Findings

Detection of a jet component ejected around 2005.9

Core position deviates from $ u^{-1}$ dependence during flare

Jet parameters suggest an over-pressured jet perturbed by shocks

Abstract

The 2006 radio flare in the blazar CTA102 is the largest ever reported for this source. The analysis of the single--dish light curves revealed a possible shock-shock interaction as a scenario for the 2006 outburst. In order to confirm this hypothesis we analyzed eight multi-frequency (2 GHz - 86 GHz) VLBI observations covering the 2006 flare. We detected a radio component ejected around 2005.9 and a stationary feature around 0.1 mas away from the core. We also performed a core-shift and spectral analysis on the fully calibrated VLBI maps. The frequency dependent position of the core slightly deviates from the typical $\nu^{-1}$-dependence during the flaring state. This behaviour may reflect a mismatch between magnetic energy density and energy density of the relativistic particles. From the core-shift corrected maps we obtained the spectral parameters and computed the temporal and spatial evolution of the jet intrinsic parameters such as the magnetic field and the particle density. The overall picture of the source could be best interpreted as an over-pressured jet perturbed by traveling shock waves.