The beaming effect for Fermi-LAT-detected FR-I radio galaxies

• Published in: arXiv.org 2023-05
• Main Authors: Xu-Hong, Ye, Xiang-Tao, Zeng, Dan-Yi, Huang, Zhang, Zhuang, Zhi-Yuan Pei, Jun-Hui, Fan
• Format: Article
• Language: English
• Subjects: Alpha rays; BL Lacertae objects; Gamma rays; Luminosity; Physical properties; Radio galaxies
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2305.10102

Our knowledge of Giga-electron volt (GeV) radio galaxies has been revolutionized by the Fermi-LAT Telescope, which provides an excellent opportunity to study the physical properties of GeV radio galaxies. According to the radio power and morphology, radio galaxies can be separated into Fanaroff-Riley Type I radio galaxies (FR-Is) and Type II radio galaxies (FR-IIs). In this paper, we consider the unification of FR-Is and BL Lacertae objects (BL Lacs), and assume FR-Is to be a standard candle to discuss the beaming effect for Fermi-LAT-detected FR-Is. Our main conclusions are as follows: (1) The estimated Doppler factors for 30 Fermi-LAT-detected FR-Is are in a range of \(\delta_{\rm{I}}=0.88-7.49\). The average Doppler factor (\(=2.56\pm0.30\)) of the 30 FR-Is is smaller than that (\(=10.28\pm2.03\)) of the 126 Fermi-LAT-detected BL Lacs, supporting the unification model that FR-Is are regarded as the misaligned BL Lacs with smaller Doppler factors; (2) We propose that different regions of FR-Is in the plot of the \(\gamma\)-ray luminosity against the photon spectral index \((\log L_{\gamma}-\alpha_{\rm{ph}})\) may indicate the different beaming effects; (3) The average Doppler factor of the 6 TeV FR-Is is similar to that of the 24 non-TeV FR-Is, which implies that the difference between the TeV and GeV emissions is not driven by the beaming effect in the Fermi-LAT-detected FR-I samples.