RoboPol: Connection between optical polarization plane rotations and gamma-ray flares in blazars

TL;DR

This study confirms a connection between optical polarization plane rotations and gamma-ray flares in blazars, showing that these events are closely related in time and amplitude, with implications for relativistic boosting effects.

Contribution

It provides the first comprehensive analysis linking polarization rotations with gamma-ray flares in a large blazar sample using RoboPol and Fermi-LAT data.

Findings

Polarization plane rotations are related to gamma-ray flares in blazars.

Time lags between rotations and flares are consistent with zero.

Rotation amplitudes are anticorrelated with gamma-ray flare amplitudes.

Abstract

We use results of our 3 year polarimetric monitoring program to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by {\em RoboPol} is analysed together with the gamma-ray data provided by {\em Fermi}-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time scales of rotations and flares are marginally correlated.