Propagation of very high energy γ-rays inside massive binaries LS 5039 and LSI+61° 303

Two massive binary systems of the microquasar type, LS 5039 and LSI +61 degrees 303, have been suggested as possible counterparts of EGRET sources. LS 5039 has also been recently detected in TeV gamma-rays. Since the massive stars in these binary systems are very luminous, it is expected that high-energy gamma-rays, if injected relatively close to the massive stars, should be strongly absorbed, initiating inverse Compton e(+/-) pair cascades in the anisotropic radiation from stellar surfaces. We investigate the influence of the propagation effects on the spectral and angular features of the gamma-ray spectra emerging from these two binary systems by applying the Monte Carlo method. Two different hypotheses are considered: isotropic injection of primary gamma-rays with the power-law spectrum due to e.g. interaction of hadrons with the matter of the wind, and the isotropic injection of electrons, e.g. accelerated in the jet, which comptonize the radiation from the massive star. It is concluded that the propagation effects of gamma-rays can be responsible for the spectral features observed from LS 5039 (e.g. the shape of the spectrum in the GeV and TeV energy ranges and their relative luminosities). The cascade processes occurring inside these binary systems significantly reduce the gamma-ray opacity obtained in other works by simple calculations of the escape of gamma-rays from the radiation fields of the massive stars. Both systems provide very similar conditions for the TeV gamma-ray production at the periastron passage. Any TeV gamma-ray flux at the apastron passage in LSI +61 degrees 303 will be relatively stronger with respect to its GeV flux than in LS 5039. If gamma-rays are produced inside these binaries not far from the massive stars, i.e. within a few stellar radii, then clear anticorrelation between the GeV and TeV emission should be observed, provided that primary gamma-rays at GeV and TeV energies are produced in the same process by the same population of relativistic particles. These gamma-ray propagation features can be tested in the near future by the multiwavelength campaigns engaging the AGILE and GLAST telescopes (> 30 MeV) and the Cherenkov telescopes (> 100 GeV, e.g. MAGIC, HESS, VERITAS and CANGAROO).