A Combined Analysis of Clusters of Galaxies - Gamma Ray Emission from
  Cosmic Rays and Dark Matter
  Multiwavelength observations suggest that clusters are reservoirs of vast
amounts relativistic electrons and positrons that are either injected into and
accelerated directly in the intra-cluster medium, or produced as secondary
pairs by cosmic ray ions scattering on ambient protons. In these possible
scenarios gamma rays are produced either through electrons upscattering
low-energy photons or by decay of neutral pions produced by hadronic
interactions. In addition, the high mass-to-light ratios in clusters in
combination with considerable Dark Matter (DM) overdensities makes them
interesting targets for indirect DM searches with gamma rays. The resulting
signals are different from known point sources or from diffuse emission and
could possibly be detected with the Fermi-LAT. Both WIMP annihilation/decay
spectra and cosmic ray induced emission are determined by universal parameters,
which make a combined statistical likelihood analysis feasible. We present
initial results of this analysis leading to limits on the DM annihilation cross
section or decay time and on the hadron injection efficiency.
