Radio core dominance of Fermi-LAT selected AGNs

TL;DR

This study analyzes a large sample of AGNs to compare radio core dominance and spectral properties between Fermi-detected and non-detected sources, revealing that Fermi blazars are predominantly beamed with higher core dominance.

Contribution

It provides a comprehensive analysis of radio and gamma-ray properties of AGNs, demonstrating the link between core dominance, spectral indices, and gamma-ray emission in Fermi-detected blazars.

Findings

Fermi-detected AGNs have higher core dominance parameters than non-Fermi AGNs.

Radio spectral indices differ significantly among AGN subclasses.

Gamma-ray emissions in Fermi blazars mainly originate from the core component, indicating strong beaming.

Abstract

Aims. We present a sample of 4388 AGNs with available radio core-dominance parameters defined as the ratio of the core flux densities to extended ones, namely, R = Score/Sext., which includes 630 Fermi-detected AGNs respect to the catalog of 4FGL, the fourth Fermi Large Area Telescope source catalog, and the rest of them are non-Fermi-detected AGNs. In our sample, 584 blazars are Fermi-detected and 1310 are not, and also consists of other subclasses such as Seyfert, Fanaroff-Riley I/II and normal galaxies. We investigate various different properties between Fermi-detected AGNs and non-Fermi-detected ones by using the core-dominance parameters as the previous study has shown that R is a good indication of beaming effect. Methods. We then calculate the radio spectral indices for whole sample and adopt {\gamma}-ray photon indices for Fermi AGNs from 4FGL catalog for discussing their different performances on different subclasses, and obtain the relation between core-dominance parameters and radio spectral indices for both Fermi and non-Fermi sources according to the two components model on radio band, which are consistent with our previous study. Results. We found that the core-dominance parameters and radio spectral indices are quite different for different subclasses of AGNs, not only for Fermi sources but also non-Fermi sources, particularly, R for the former ones is averagely higher than later ones. We also adopt the same relation on core-dominance parameters and {\gamma}-ray photon indices for Fermi sources by taking the same assumption with two components model on {\gamma}-ray band, and obtain the fitting results indicating that the {\gamma}-ray emissions of Fermi blazars are mainly from the core component, which is perhaps associated with the beaming effect. Therefore, Fermi blazars are beamed.