Nonthermal x rays from the Ophiuchus galaxy cluster and dark matter annihilation

We investigate a scenario where the recently discovered nonthermal hard x-ray emission from the Ophiuchus cluster originates from inverse Compton scattering of energetic electrons and positrons produced in weakly interacting dark matter pair annihilations. We show that this scenario can account for both the x ray and the radio emission, provided the average magnetic field is of the order of 0.1 mu G. We demonstrate that Gamma-Ray Large Area Telescope (GLAST) will conclusively test the dark matter annihilation hypothesis. Depending on the particle dark matter model, GLAST might even detect the monochromatic line produced by dark matter pair annihilation into two photons.