Cen A as gamma- and UHE cosmic-ray Source
  Cen A has been recently detected in the high-energy (HE) and very high energy (VHE) gamma-ray domain by Fermi-LAT and H.E.S.S. We review the observed characteristics and suggest a scenario where the VHE emission originates from the vicinity of the black hole. Motivated by the possible association of some ultra-high energy (UHE) cosmic ray (CR) events with Cen A, we further analyze the acceleration efficiency for a number of a mechanisms (including shock and stochastic acceleration), showing that most of them (apart perhaps from shear) have serious difficulties in accelerating protons beyond a few $10^{19}$ eV. 
F.M. Rieger
astro-ph.HE