Parsec-Scale Behavior of Blazars during High Gamma-Ray States

TL;DR

This study analyzes the correlation between gamma-ray activity and radio flux and polarization in blazars, suggesting gamma-ray outbursts originate outside the broad line region, near or downstream of the VLBI core.

Contribution

It provides multi-wavelength observational evidence linking gamma-ray flares with radio core and jet polarization changes in blazars, indicating their emission regions are outside the broad line region.

Findings

Gamma-ray peaks coincide with increases in radio flux and polarization.

Many gamma-ray outbursts occur outside the broad line region.

Radio and polarization changes are contemporaneous with gamma-ray activity.

Abstract

We compare the \gamma-ray light curves of the blazars, constructed with data provided by the Fermi Large Area Telescope, with flux and polarization variations in the VLBI core and bright superluminal knots obtained via monthly monitoring with the Very Long Baseline Array at 43 GHz. For all blazars in the sample that exhibit a high \gamma-ray state on time scales from several weeks to several months, an increase of the total flux in the mm-wave core is contemporaneous with the \gamma-ray activity (more than a third of the sample). Here we present the results for quasars with the most extreme \gamma-ray behavior (3C 454.3, 3C 273, 3C 279, 1222+216, and 1633+382). The sources show that in addition to the total flux intensity behavior, a maximum in the degree of polarization in the core or bright superluminal knot nearest to the core coincides with the time of a \gamma-ray peak to within the accuracy of the sampling of the radio data. These argue in favor of location of many of \gamma-ray outbursts in blazars outside of the broad line region, either in the vicinity or downstream of the mm-wave VLBI core.