Discovery of gamma-ray emission from the Broad Line Radio Galaxy Pictor A

Abstract

We report the discovery of high-energy γ-ray emission from the Broad Line Radio Galaxy (BLRG) Pictor A with a significance of ~5.8σ(TS=33.4), based on three years of observations with the Fermi Large Area Telescope (LAT) detector. The three-year averaged E>0.2 GeV γ-ray spectrum is adequately described by a power-law, with a photon index, Γ, of $2.93\pm 0.03$ and a resultant integrated flux of $F_{\gamma }=(5.8\pm 0.7)\times 10^{-9}$ ph cm${}^{-2}$s${}^{-1}$. A temporal investigation of the observed γ-ray flux, which binned the flux into year long intervals, reveals that the flux in the third year was 50% higher than the three-year average flux. This observation, coupled with the fact that this source was not detected in the first two years of {Fermi-LAT observations, suggests variability on timescales of a year or less. Synchrotron Self-Compton modelling of the spectral energy distribution of a prominent hot-spot in Pictor A's western radio lobe is performed. It is found that the models in which the γ-ray emission originates within the lobes, predicts an X-ray flux larger than that observed. Given that the X-ray emission in the radio lobe hot-spots has been resolved with the current suite of X-ray detectors, we suggest that the γ-ray emission from Pictor A originates from within its jet, which is in agreement with other γ-ray loud BLRGs. This suggestion is consistent with the evidence that the γ-ray flux is variable on timescales of a year or less.

Accepted for publication in MNRAS: 8 pages, 3 figures, 1 table

References in corpus (16)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Fermi Large Area Telescope Second Source Catalog
• The Second Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• Radio-Loudness of Active Galactic Nuclei: Observational Facts and Theoretical Implications
• Fermi Large Area Telescope Bright Gamma-ray Source List
• Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
• Fermi Gamma-ray Imaging of a Radio Galaxy
• Time-Integrated Searches for Point-like Sources of Neutrinos with the 40-String IceCube Detector
• The multiwavelength variability of 3C 273
• Variable VHE gamma-ray emission from non-blazar AGNs
• First Search for Point Sources of High Energy Cosmic Neutrinos with the ANTARES Neutrino Telescope
• Structure of the Accretion Flow in Broad-Line Radio Galaxies: The Case of 3C390.3
• A high resolution view of the jet termination shock in a hot spot of the nearby radio galaxy Pictor A: implications for X-ray models of radio galaxy hot spots
• Upper Limits from HESS AGN Observations in 2005-2007
• Radio Lobes of Pictor A: an X-ray spatially resolved Study
• Origin of the X-rays and Possible GeV-TeV Emission from the Western Hot Spot Of Pictor A

Cited by in corpus (18)

• The Second Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
• Diffuse $\gamma$-ray emission from misaligned active galactic nuclei
• VLBI and Single Dish Monitoring of 3C84 in the Period of 2009-2011
• 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
• An upper limit on the cosmic-ray luminosity of individual sources from gamma-ray observations
• Spectroscopic classification, variability and SED of the Fermi-detected CSS 3C 286: the radio-loudest NLS1 galaxy?
• Examining High Energy Radiation Mechanisms of Knots and Hotspots in Active Galactic Nucleus Jets
• Evaluating the Gamma-Ray Evidence for Self-Annihilating Dark Matter from the Virgo Cluster
• Application of the spine-layer jet radiation model to outbursts in the broad-line radio galaxy 3C 120
• $\gamma$-ray observations of extraterrestrial neutrino track event positions
• The nature of the multi-wavelength emission of 3C 111
• Discovery of gamma-ray emission from a strongly lobe-dominated quasar 3C 275.1
• Non-thermal emission in lobes of radio galaxies: III. 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236
• Multiwavelength study of radio galaxy Pictor A: detection of western hotspot in far-UV and possible origin of high energy emissions
• Very High Energy gamma-ray emission from RBS 0970
• Very high energy $\gamma$-ray emission from RBS 0679
• Complex Structure of the Eastern Lobe of the Pictor A Radio Galaxy: Spectral Analysis and X-ray/Radio Correlations