Catching the radio flare in CTA 102 I. Light curve analysis

TL;DR

This study analyzes the spectral evolution of the 2006 radio flare in blazar CTA 102 using multifrequency observations, testing shock-in-jet models and suggesting shock-shock interactions as a key mechanism.

Contribution

It provides a detailed spectral analysis of a major flare in CTA 102, incorporating Monte Carlo simulations and modeling to explore shock interactions beyond simple geometrical explanations.

Findings

Double peak structure in spectral evolution.

Discards pure geometrical explanations for the double peak.

Supports shock-shock interaction as a physical mechanism.

Abstract

Context: The blazar CTA 102 (z=1.037) underwent a historical radio outburst in April 2006. This event offered a unique chance to study the physical properties of the jet. Aims: We used multifrequency radio and mm observations to analyze the evolution of the spectral parameters during the flare as a test of the shock-in-jet model under these extreme conditions. Methods: For the analysis of the flare we took into account that the flaring spectrum is superimposed on a quiescent spectrum. We reconstructed the latter from archival data and fitted a synchrotron self-absorbed distribution of emission. The uncertainties of the derived spectral parameters were calculated using Monte Carlo simulations. The spectral evolution is modeled by the shock-in-jet model, and the derived results are discussed in the context of a geometrical model (varying viewing angle) and shock-shock interaction. Results: The evolution of the flare in the turnover frequency-turnover flux density plane shows a double peak structure. The nature of this evolution is dicussed in the frame of shock-in-jet models. We discard the generation of the double peak structure in the turnover frequency-turnover flux density plane purely based on geometrical changes (variation of the Doppler factor). The detailed modeling of the spectral evolution favors a shock-shock interaction as a possible physical mechanism behind the deviations from the standard shock-in-jet model.