  Colliding winds of massive binaries have long been considered as potential
sites of non-thermal high-energy photon production. This is motivated by the
detection of non-thermal spectra in the radio band, as well as by correlation
studies of yet unidentified EGRET gamma-ray sources with source populations
appearing in star formation regions. This work re-considers the basic radiative
processes and its properties that lead to high energy photon production in
long-period massive star systems. We show that Klein-Nishina effects as well as
the anisotropic nature of the inverse Compton scattering, the dominating
leptonic emission process, likely yield spectral and variability signatures in
the gamma-ray domain at or above the sensitivity of current or upcoming gamma
ray instruments like GLAST-LAT. In addition to all relevant radiative losses,
we include propagation (such as convection in the stellar wind) as well as
photon absorption effects, which a priori can not be neglected. The
calculations are applied to WR140 and WR147, and predictions for their
detectability in the gamma-ray regime are provided. Physically similar specimen
of their kind like WR146, WR137, WR138, WR112 and WR125 may be regarded as
candidate sources at GeV energies for near-future gamma-ray experiments.
Finally, we discuss several aspects relevant for eventually identifying this
source class as a gamma-ray emitting population. Thereby we utilize our
findings on the expected radiative behavior of typical colliding wind binaries
in the gamma-ray regime as well as its expected spatial distribution on the
gamma-ray sky.
