We report the discovery of a statistically significant hardening in the
Fermi-LAT γ-ray spectrum of Centaurus A's core, with the spectral index
hardening from Γ1=2.73±0.02 to Γ1=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 lightcurve above or below the
spectral break when considering the entire 8 year period. Interestingly,
however, the first ∼3.5 years of the low energy lightcurve shows evidence
of flux variability at the ∼3.5σ 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 γ-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 γ-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.Comment: 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 versio