Suzaku X-ray Imaging of the Extended Lobe in the Giant Radio Galaxy NGC6251 Associated with the Fermi-LAT Source 2FGLJ1629.4+8236

Abstract

We report the results of a Suzaku X-ray imaging study of NGC6251, a nearby giant radio galaxy with intermediate FR I/II radio properties. Our pointing direction was centered on the gamma -ray emission peak recently discovered with Fermi-LAT around the position of the north-west radio lobe 15 arcmin offset from the nucleus. After subtracting two "off-source" pointings adjacent to the radio lobe, and removing possible contaminants in the XIS field of view, we found significant residual X-ray emission most likely diffuse in nature. The spectrum of the excess X-ray emission is well fit by a power law with photon index Γ= 1.90 +- 0.15 and a 0.5 - 8 keV flux of 4 x 10^{-13} erg cm^{-2} s^{-1}. We interpret this diffuse X-ray emission component as being due to inverse-Compton up-scattering of the cosmic microwave background photons by ultrarelativistic electrons within the lobe, with only a minor contribution from the beamed emission of the large-scale jet. Utilizing archival radio data for the source, we demonstrate by means of broad-band spectral modeling that the -ray flux of the Fermi-LAT source 2FGL J1629.4+8236 may well be accounted for by the high-energy tail of the inverse-Compton continuum of the lobe. Thus, this claimed association of gamma-rays from the north-west lobe of NGC6251, together with the recent Fermi-LAT imaging of the extended lobes of Centaurus A, indicates that particles may be efficiently (re-)accelerated up to ultrarelativistic energies within extended radio lobes of nearby radio galaxies in general.

19 pages, 4 figures, accepted for publication in the ApJ

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Cited by in corpus (18)

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• The Extragalactic Gamma-ray Sky in the Fermi era
• Discovery of GeV Emission from the Circinus galaxy with the Fermi-LAT
• Giant Lobes of Centaurus A Radio Galaxy Observed with the Suzaku X-ray Satellite
• Suzaku Observations of gamma-Ray Bright Radio Galaxies: Origin of the X-ray Emission and Broad-Band Modelin
• Multiwavelength Astronomy and CTA: X-rays
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• Fermi-LAT and Suzaku Observations of the Radio Galaxy Centaurus B
• Examining High Energy Radiation Mechanisms of Knots and Hotspots in Active Galactic Nucleus Jets
• Low-frequency observations of the Giant Radio Galaxy NGC 6251
• Constraints on the gamma-ray emission from the cluster-scale AGN outburst in the Hydra A galaxy cluster
• Non-thermal emission in radio galaxy lobes: II. Centaurus A, Centaurus B, and NGC 6251
• Analysis of Fermi-LAT observations, UHECRs and neutrinos from the radio galaxy Centaurus B
• JD6 - The Connection between Radio Properties and High Energy Emission in AGNs