Discovery of a new extragalactic source population of energetic particles

Understand

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 $\sim3.5$ years of the low energy lightcurve shows evidence of flux variability at the $\sim3.5 \sigma$ 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.