Fermi Large Area Telescope Observations of Misaligned AGN

TL;DR

This study analyzes 15 months of Fermi-LAT data to detect gamma-ray emissions from 11 misaligned AGNs, revealing new sources, spectral properties, and implications for AGN unification models.

Contribution

First detection of gamma-ray emission from the broad line FRI radio galaxy 3C 120 and detailed spectral analysis of various misaligned AGNs.

Findings

7 of 11 sources have spectral indices > 2.3

No significant variability observed except in NGC 1275

Gamma-ray luminosities differ between FRI and FRII sources

Abstract

Analysis is presented on 15 months of data taken with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope for 11 non-blazar AGNs, including 7 FRI radio galaxies and 4 FRII radio sources consisting of 2 FRII radio galaxies and 2 steep spectrum radio quasars. The broad line FRI radio galaxy 3C 120 is reported here as a gamma-ray source for the first time. The analysis is based on directional associations of LAT sources with radio sources in the 3CR, 3CRR and MS4 (collectively referred to as 3C-MS) catalogs. Seven of the eleven LAT sources associated with 3C-MS radio sources have spectral indices larger than 2.3 and, except for the FRI radio galaxy NGC 1275 that shows possible spectral curvature, are well described by a power law. No evidence for time variability is found for any sources other than NGC 1275. The gamma-ray luminosities of FRI radio galaxies are significantly smaller than those of BL Lac objects detected by the LAT, whereas the gamma-ray luminosities of FRII sources are quite similar to those of FSRQs, which could reflect different beaming factors for the gamma-ray emission. A core dominance study of the 3CRR sample indicate that sources closer to the jet axis are preferentially detected with the Fermi-LAT, insofar as the gamma-ray--detected misaligned AGNs have larger core dominance at a given average radio flux. The results are discussed in view of the AGN unification scenario.