Discovery of a new extragalactic population of energetic particles

We report the discovery of a statistically significant hardening in the Fermi-LAT gamma-ray spectrum of CentaurusA's (Cen A) core, with the spectral index hardening from Gamma(1) = 2.73 +/- 0.02 to Gamma(1) = 2.29 +/- 0.07 at a break energy of (2.6 +/- 0.3) GeV. Using a likelihood analysis, we find no evidence for flux variability in Cen A's core light curve above or below the spectral break when considering the entire 8 year period. Interestingly, however, the first similar to 3.5 years of the low energy light curve shows evidence of flux variability at the similar to 3.5s 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.