  Centaurus A, the cosmic ray accelerator a few Mpc away from us is possibly
one of the nearest sources of extremely high energy cosmic rays. We investigate
whether the gamma ray data currently available from Centaurus A in the GeV-TeV
energy band can be explained with only proton proton interactions. We show that
for a single power law proton spectrum, mechanisms of $\gamma$-ray production
other than proton proton interactions are needed inside this radio-galaxy to
explain the gamma ray flux observed by EGRET, upper limits by
H.E.S.S./CANGAROO-III and the correlated extremely energetic cosmic ray events
observed by the Pierre Auger experiment. In future with better $\gamma$-ray
data, simultaneous observation with $\gamma$-ray and cosmic ray detectors, it
would be possible to carry out such studies on different sources in more
detail.
