1997A&A...322..523B

Two massive binaries, Cyg X-3 and LSI +61 303, are inside the error boxes of γ-ray sources detected by the Compton GRO. If somewhere inside such binary systems are injected very high energy (VHE) γ-rays, as suggested by some Cherenkov observations, they may initiate the inverse Compton e^± pair cascade in the soft radiation of a massive companion, and the detected high energy γ-ray emission may be caused by the secondary γ-rays of such cascade process. Since VHE γ-rays has to propagate in the anisotropic radiation of a massive star (the place of injection does not cover with the source of soft radiation), the intensities of secondary γ-rays depend on the angles of observation measured from direction defined by the place of injection of VHE γ-rays and the center of a massive star. We compute γ-ray spectra formed in such anisotropic cascade by using the Monte Carlo method. It is found that the intensity of secondary γ-rays does not varies strongly for the angles of observation greater than ∼90°, but the highest intensities are observed at the angles corresponding to the limb of a massive star. Moreover, some cascade γ-rays can also emerge from behind the massive star, i.e. from the opposite site than the location of a source of primary γ-rays. This interesting feature can be called as a focusing of γ-rays by the soft radiation of a massive star.