Figure 1: A schematic of the different sources and energy distributions of -rays from WIMP annihilation. (a) Secondary photons arising from the decay of neutral pions produced in the hadronization of primary annihilation products. (b) Internal bremsstrahlung photons associated with charged annihilation products, either in the form of final state radiation (FSR) from external legs or as virtual internal bremsstrahlung (VIB) from the exchange of virtual charged particles. (c) Monochromatic line signals from the prompt annihilation into two photons or a photon and boson. This process occurs only at loop level, and hence is typically strongly suppressed.