Characterizing Gamma-Radio Delayed Flaring Activity from Blazars

TL;DR

This study investigates multi-year delayed correlations between gamma-ray and radio flares in blazars, revealing delays of 180 days on average, and highlights the importance of extended radio emission in understanding jet activity.

Contribution

It introduces a comprehensive analysis of long-term gamma-ray and radio correlations in blazars, utilizing Gaussian process modeling and a large dataset, including morphological data from MOJAVE.

Findings

Several sources show delayed radio flares of 1-3 years.

Stacked analysis indicates a peak correlation at about 180 days delay.

Delayed radio emission is a common feature in the blazar population.

Abstract

Flaring activity from the jets of active galactic nuclei has been studied for several decades, closely related to the loading and evolution of the jet. In this work, we focus on the sub-hundred parsec jet region, well traced by non-thermal radio and gamma-ray emission. Only in recent years have light curves capturing the decade-long behavior of such sources become available for a large ensemble of objects. While previous studies have focused on a direct correlation or few-month lag between gamma-ray and radio activity, recent neutrino-bright blazars observed by the IceCube Neutrino Observatory present multi-year delays between initial gamma-ray activity and subsequent radio flares. In this work, we search for similar-timescale correlations between Fermi-LAT gamma-ray data and RATAN-600 radio data from ~100 blazars. We consider two gamma-ray bands, 100 MeV-1 GeV and 1 GeV-500 GeV, as well as the integral band, to compare correlations between potential opaque and unabsorbed regions of the jet. Gaussian process modeling is used for smooth light curve function prediction. We also analyze morphological AGN core data from the MOJAVE survey, forming a sub-selection to better illustrate potential dependence on location. In the broader selection, several sources exhibit delayed flares on the order of 1-3 years. In the stacked analysis, we find the highest correlation for a radio delay on the order of 180 days. The stacked correlation resulting from the MOJAVE sub-selection corresponds to a slightly smaller time lag. Delayed radio flares or extended radio emission appear to be notable features within the general blazar population.