A comprehensive study on the variation phenomena of AO 0235+164

TL;DR

This study analyzes multi-wavelength data of blazar AO 0235+164, revealing correlated emission regions, complex flux and polarization variability patterns, and proposing a helical jet model with changing viewing angles as a key explanation.

Contribution

It provides a comprehensive multi-wavelength correlation analysis and introduces a helical jet model to explain complex variability in AO 0235+164.

Findings

Gamma-ray and optical emissions are correlated and originate from regions beyond the broad line region.

Optical color index shows RWB at low flux and BWB at high flux states.

Polarization and flux flares are not synchronous and exhibit inverse rotation trajectories.

Abstract

The variation mechanism of blazars is a long standing open question. The polarization observation can provide us with more information to constrain models. In this work, we collect the long term multi-wavelength data of AO 0235+164, and make correlation analysis between them by using the local cross-correlation function (LCCF). We found that both $\gamma$-ray and the optical {\it V}-band light curves are correlated with the radio light curve at beyond 3$\sigma$ significance level. The emitting regions of the $\gamma$-ray and the optical coincide within errors, and locate at {$6.6_{-1.7}^{+0.6}$} pc upstream of the core region of 15 GHz, which are beyond the broad line region (BLR). The color index shows the redder when brighter (RWB) trend at the low flux state, but turns to the bluer when brighter (BWB) trend at the high flux state. While, the $\gamma$-ray spectral index always shows the softer when brighter (SWB) trend. We propose that such complex variation trends can be explained by the increasing jet component with two constant components. The {optical} PD flares and {optical} flux flares are not synchronous. It seems that one flux peak are sandwiched by two PD peaks, which have inverse rotation trajectories in the $qu$ plane. The helical jet model can schematically show these characteristics of polarization with fine tuned parameters. The change of viewing angle is suggested to be the primary variable which lead all these variations, although other possibilities like the shock in jet model or the hadronic model are not excluded completely.