  High energy gamma-rays have been detected from Cygnus X-3, a system composed
of a Wolf-Rayet star and a black hole or neutron star. The gamma-ray emission
is linked to the radio emission from the jet launched in the system. The flux
is modulated with the 4.8 hr orbital period, as expected if high energy
electrons are upscattering photons emitted by the Wolf-Rayet star to gamma-ray
energies. This modulation is computed assuming that high energy electrons are
located at some distance along a relativistic jet of arbitrary orientation.
Modeling shows that the jet must be inclined and that the gamma ray emitting
electrons cannot be located within the system. This is consistent with the idea
that the electrons gain energy where the jet is recollimated by the stellar
wind pressure and forms a shock. Jet precession should strongly affect the
gamma-ray modulation shape at different epochs. The power in non-thermal
electrons represents a small fraction of the Eddington luminosity only if the
inclination is low i.e. if the compact object is a black hole.
