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  • Radio core dominance of Fer...
    Pei, ZhiYuan; Fan, JunHui; Bastieri, Denis; Yang, JiangHe; Xiao, HuBing

    Science China. Physics, mechanics & astronomy, 05/2020, Letnik: 63, Številka: 5
    Journal Article

    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.