Propagation of very high energy gamma-rays inside massive binaries LS   5039 and LSI +61 303
  It is expected that high energy gamma-rays, if injected relatively close to the massive stars in binary systems LS 5039 and LSI 61 3003, should be strongly absorbed, initiating inverse Compton $e^\pm$ pair cascades in the anisotropic radiation from stellar surfaces. We investigate 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 hypothesis are considered: isotropic injection of primary gamma-rays with the power law spectrum and electrons. It is concluded that propagation effects of gamma-rays can be responsible for the spectral features observed from LS 5039. 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 +61 303 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 multi-wavelength campaigns engaging the AGILE and GLAST telescopes and the Cherenkov telescopes (e.g. MAGIC, HESS, VERITAS and CANGAROO). 
W. Bednarek