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A few high-mass X-ray binaries–consisting of an OB star plus compact companion–\udhave been observed by Fermi and\udground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE;\udup to 30 TeV) γ-rays. This paper focuses on the prominent γ-ray source, LS 5039, which consists of a massive O6.5V star\udin a 3.9-day-period, mildly elliptical (e ≈ 0.24) orbit with its companion, assumed here to be an unmagnetized compact\udobject (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion\udof the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very\udclosely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model,\udwherein intrinsic emission of γ-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of\udthe phase variation of γ-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the\udHESS Cerenkov telescope,\udit is important to account also for photon-photon interactions between the γ-rays and the stellar\udoptical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included,\udwe find that this simple BHL accretion model also quite naturally\udfits the HESS light curve, thus making it a strong alternative\udto the pulsar-wind-shock models commonly invoked to explain such VHE γ-ray emission in massive-star binaries

Modeling Gamma-Ray Emission From the High-Mass X-Ray Binary LS 5039