  There is compelling evidence that at least some clusters of galaxies are
powerful sources of non-thermal radiation. In all cases where this radiation
has been detected, a general trend is that high energy densities of cosmic rays
and correspondingly low values of the average magnetic field are required in
order to have a self-consistent picture of the multiwavelength observations.
Mergers of clusters of galaxies might provide large enough cosmic ray injection
rates and at the same time provide the mechanism for the heating of the
intracluster medium to the observed temperatures. In this paper we analyze
critically all the components that play a role in the non-thermal emission of
clusters during a merger, with special attention to mergers occurred in the
past of the cluster. We outline the consequences of this model for high energy
gamma ray observations and for Faraday rotation measurements of the
intracluster magnetic field.
