Radio core dominance of Fermi/LAT-detected AGNs

• Published in: Science China. Physics, mechanics & astronomy mechanics & astronomy, 2020-05, Vol.63 (5), p.259511, Article 259511
• Main Authors: Pei, ZhiYuan, Fan, JunHui, Bastieri, Denis, Yang, JiangHe, Xiao, HuBing
• Format: Article
• Language: English
• Subjects: Accretion disks; Active galactic nuclei; Astronomy; Blazars; Classical and Continuum Physics; Energy; Galaxies; Gamma emission; Mathematical models; Observations and Techniques; Parameters; Photons; Physics; Physics and Astronomy; Science; Space telescopes; Stars & galaxies
• ISSN: 1674-7348; 1869-1927
• DOI: 10.1007/s11433-019-1454-6

We present a sample of 4388 AGNs with available radio core-dominance parameters—defined as the ratio of the core flux densities to the extended ones, R = S core / S ext .—which includes 630 Fermi -detected AGNs from the fourth source catalog (4FGL) of the Fermi Large Area Telescope ( Fermi /LAT); the rest are non- Fermi -detected AGNs. In our sample, 584 blazars are Fermi -detected and 1310 are not. The sample also contains other subclasses, such as Seyferts, Fanaroff-Riley I/II galaxies, and normal galaxies. We investigate various properties of the Fermi -detected and non- Fermi -detected AGNs by using core-dominance parameters, capitalizing on a previous study which showed that R is a good indicator of beaming. We then calculate radio spectral indices for the whole sample, and adopt γ -ray-photon indices for the Fermi AGNs from the 4FGL catalog to discuss the properties of different subclasses. We obtain a relation between the core-dominance parameters and the radio spectral indices for both Fermi and non- Fermi sources, assuming a two-component model in the radio band. Our previous study ruled out the assumption that the core-dominance parameters and radio spectral indices are quite different for different AGN subclasses. This holds not only for Fermi sources but also for non- Fermi sources. In particular, R is, on average, greater for the former AGNs than for the latter. In this study, we enlarge our sample with available values of R to 4388 AGNs, and the obtained conclusions are consistent with our previous study. We assume that the same two-component model holds for the γ -ray band as for the radio band, and therefore, adopt the same relation between the core-dominance parameters and the γ -ray-photon indices for Fermi AGNs. Our fitting results indicate that the γ -ray emissions of Fermi blazars originate mainly from the jet, and therefore, we conclude that the Fermi blazars are beamed.