2026/08/02 by Xu-Hong Ye, Wen-Xin Yang, Guo-Hai Chen +5
Physics and Astronomy · #astro-ph.HE
9 pages, 5 figures, accepted by MNRAS
arxiv created 2026/08/02 · arxiv published 2026/08/02 · arxiv updated 2026/08/04
Radio and γ-ray emissions in blazars, a subclass of active galactic nuclei (AGNs), provide important insight into their high-energy radiation processes. We studied the relation between radio and γ-ray emissions using a large sample of 1687 Fermi blazars, based on the Radio Fundamental Catalogue and the latest Third Data Release of the Fourth Fermi AGN Catalogue. A clear correlation between radio and γ-ray fluxes for both BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) suggests a synchrotron self-Compton (SSC) contribution to both subclasses. The ratio of γ-ray and radio emissions, γ-ray loudness (G\rm r), is further examined with the γ-ray photon index (Γγ) and the synchrotron peak frequency (ν_\rmpeak). An anti-correlation between G\rm r and Γγ is explained by the shift of the spectral energy distribution rather than the Compton cooling effect. We found that G\rm r shows a positive dependence on ν_\rmpeak for low-synchrotron-peaked BL Lacs (LBLs) and FSRQs, in line with the SSC-contributed scenario, although additional external Compton contributions may account for the substantial scatter observed in LBLs and FSRQs. In contrast, high-synchrotron-peaked BL Lacs (HBLs) reach the plateau of G\rm r between log (ν\rm peak/\rm Hz) ≃15.5-16, possibly indicating the transition from the Thomson to the Klein--Nishina (KN) regime. Interpreting this feature within a one-zone SSC framework could constrain the magnetic field strength of -4.14 < log (B/\rm G) < -1.69 for those HBLs affected by the KN suppression.