On the radio and GeV-TeV gamma-ray emission connection in Fermi blazars

TL;DR

This study investigates the connection between high-resolution radio emission and gamma-ray emission in blazars, revealing a strong correlation at lower energies but a diminished link at very high energies, except for certain blazar types.

Contribution

The paper provides a comprehensive analysis of the radio and gamma-ray emission correlation in blazars across different energy ranges, highlighting the energy-dependent nature of this relationship.

Findings

Strong correlation between radio and gamma-ray emission in 0.1-300 GeV range.

Correlation diminishes above 10 GeV, except for high synchrotron peaked blazars.

Radio-gamma connection is energy-dependent and varies among blazar subclasses.

Abstract

The Fermi-LAT revealed that the census of the gamma-ray sky is dominated by blazars. Looking for a possible connection between radio and gamma-ray emission is a central issue for understanding the blazar physics, and various works were dedicated to this topic. However, while a strong and significant correlation was found between radio and gamma-ray emission in the 0.1-100 GeV energy range, the connection between radio and very high energy (VHE, E>0.1 TeV) emission is still elusive. The main reason is the lack of a homogeneous VHE sky coverage, due to the operational mode of the imaging atmospheric Cherenkov telescopes. With the present work we aim to quantify and assess the significance of the possible connection between high-resolution radio emission, on milliarcsecond scale, and GeV-TeV gamma-ray emission in blazars. For achieving our goal we extract two large and unbiased blazar samples from the 1FHL and 2FHL Fermi catalogs, above 10 GeV and 50 GeV, respectively. To investigate how the correlation evolves as the gamma-ray energy increases, we perform the same analysis by using the 0.1-300 GeV 3FGL gamma-ray energy fluxes. When we consider the 0.1-300 GeV gamma-ray energy range, we find a strong and significant correlation for all of the blazar sub-classes. Conversely, when we consider the gamma-ray emission above 10 GeV the correlation with the radio emission vanishes, with the exception of the blazar sub-class of high synchrotron peaked objects.