Discovery of a new extragalactic source population of energetic particles

Abstract

We report the discovery of a statistically significant hardening in the Fermi-LAT $\gamma$-ray spectrum of Centaurus A's core, with the spectral index hardening from ${\Gamma }_1=2.73\pm 0.02$ to ${\Gamma }_1=2.29\pm 0.07$ at a break energy of ($2.6\pm 0.3$) GeV. Using a likelihood analysis, we find no evidence for flux variability in Cen A's core lightcurve above or below the spectral break when considering the entire 8 year period. Interestingly, however, the first $\sim 3.5$ years of the low energy lightcurve shows evidence of flux variability at the $\sim 3.5\sigma$ confidence level. To understand the origin of this spectral break, we assume that the low energy component below the break feature originates from leptons in Centaurus A's radio jet and we investigate the possibility that the high energy component above the spectral break is due to an additional source of very high energy particles near the core of Cen A. We show for the first time that the observed $\gamma$-ray spectrum of an Active Galactic Nucleus is compatible with either a very large localized enhancement (referred to as a spike) in the dark matter halo profile or a population of millisecond pulsars. Our work constitutes the first robust indication that new $\gamma$-ray production mechanisms can explain the emission from active galaxies and could provide tantalizing first evidence for the clustering of heavy dark matter particles around black holes.

8 pages, 10 figures. Final version selected as an editor's suggestion and published in Phys. Rev. D. Updated version includes an additional reference that was missing from the final published version

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Cited by in corpus (19)

• The $\gamma$-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LAT
• Radio Galaxies at VHE energies
• Fermi-LAT Observation of Non-Blazar AGNs
• Understanding the $\gamma$-ray emission from the globular cluster 47 Tuc: evidence for dark matter?
• The complex gamma-ray behaviour of the Radio Galaxy M87
• A search for Centaurus A-like features in the spectra of Fermi-LAT detected radio galaxies
• Inverse Compton scattering of starlight in the kiloparsec-scale jet in Centaurus A: The origin of excess TeV $\gamma$-ray emission
• Radio Galaxies with the Cherenkov Telescope Array
• Signatures of leptophilic t-channel dark matter from active galactic nuclei
• Fermi-LAT Observations of Extreme Spectral Variability in IC 310
• Very high-energy gamma-ray signature of ultrahigh-energy cosmic-ray acceleration in Centaurus A
• GeV-TeV gamma-rays produced by electrons in the kpc scale jet as a result of comptonization of the inner jet emission
• A search for $\gamma$-ray emission from a sample of local universe low-frequency selected radio galaxies
• What Could be the Observational Signature of Dark Matter in Globular Clusters?
• Two blobs in a jet model for the gamma-ray emission in radio galaxies
• Cherenkov telescope array extragalactic survey discovery potential and the impact of axion-like particles and secondary gamma rays
• A Systematic Search for Spectral Hardening in Blazar Flares with the Fermi-Large Area Telescope
• Morphology of TeV gamma-ray emission from the kpc scale jets in radio galaxies
• A spectral hardening in the Fermi-LAT Data of 1ES 0502+675