  In this paper, we investigate the gamma ray signal produced from dark matter
collisions with high energy cosmic protons. Notably, we extend past results by
including important hadronization effects. Showering and hadronization produces
a high multiplicity of photons from the decays of hadrons, whose rate is not
suppressed by the fine structure constant. Notably, proton remnants that do not
participate in hard scattering, can produce a large rate of photons in the
forward direction. These effects significantly enhance the photon rate and
alter the energy and angular distributions compared to previous results which
used only parton level calculations. Due to this modification, the gamma ray
signal from the nearby active galactic nuclei Centaurus A is potentially
testable in future Fermi-LAT and HESS measurements, for a dark matter mass and
coupling consistent with current XENON100 bounds.
