Nonthermal emission from the radio relic of the galaxy cluster A2256
  We aim to obtain a consistent description of non-thermal emissions from Abell
2256 and to give a prediction for a gamma-ray emission from this galaxy
cluster. Assuming that a radio relic illuminates a localization of an ongoing
merger, and that both radio and non-thermal part of hard X-ray emission are due
to electron component of cosmic rays filling the relic, we derived from radio
and hard X-ray properties of the relic in A2256 the magnetic field strength and
number densities for relativistic electrons and protons. Due to the
interpretation of the radio relic as a structure formed just where a shock
front is, we discuss a gamma-ray emission at the cluster periphery. The
estimated strength of the magnetic field in the relic is equal to 0.05 \muG,
while the amplitude of the electron number density varies from 3 x 10^{-4} to 3
x 10^{-5} cm^{-3} (respectively for the relic thickness of 50 to 500 kpc). We
got a substantial degree of non-equipartition between cosmic rays and magnetic
field in the relic region, where the CR pressure is approaching that of thermal
gas. Our prediction for LOFAR is a synchrotron flux from the relic region of
the order of \sim 6 Jy at 60MHz and \sim 10 Jy at 30MHz. The lower limit of the
gamma-ray flux from the relic region calculated for a hadronic channel is of
the order of 10^{-12} erg cm^{-2}.
