paper

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

arXiv:astro-ph/0601657 · doi:10.1111/j.1365-2966.2006.10121.x

Abstract

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 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).

15 pages, submitted to MNRAS

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