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

Abstract

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 ${\delta }_{\mathrm{I}}=0.88-7.49$. The average Doppler factor ($<{\delta }_{\mathrm{I}}>=2.56\pm 0.30$) of the 30 FR-Is is smaller than that ($<{\delta }_{\mathrm{BL}}>=10.28\pm 2.03$) 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 $(\log L_{\gamma }-{\alpha }_{\mathrm{ph}})$ 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.

15 pages, 6 figures, 2 tables. publication in PASP

References in corpus (11)

• Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies
• Fast variability of TeV gamma-rays from the radio galaxy M 87
• Fermi Gamma-ray Imaging of a Radio Galaxy
• Black hole lightning due to particle acceleration at subhorizon scales
• On the BL Lacertae objects/radio quasars and the FRI/II dichotomy
• Jet collimation and acceleration in the giant radio galaxy NGC 315
• Gamma-ray emission in radio galaxies under the VLBI scope -- I. Parsec-scale kinematics and high-energy properties of $\gamma$-ray detected TANAMI radio galaxies
• A search for Centaurus A-like features in the spectra of Fermi-LAT detected radio galaxies
• FSRQ/BL Lac dichotomy as the magnetized advective accretion process around black holes: a unified classification of blazars
• Jet/accretion and Unification for FSRQs/FRII and BL Lac objects/FRI radio galaxies
• A search for $\gamma$-ray emission from a sample of local universe low-frequency selected radio galaxies

Cited by in corpus (1)

• Search for the multiwavelength counterparts to extragalactic unassociated Fermi γ-ray sources