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  • Gamma-rays from nebulae aro...
    Bednarek, W; Sitarek, J

    Monthly notices of the Royal Astronomical Society, 04/2013, Letnik: 430, Številka: 4
    Journal Article

    We consider nebulae which are created around binary systems containing rotation-powered pulsars and companion stars with strong stellar winds. It is proposed that the stellar and pulsar winds have to mix at some distance from the binary system, defined by the orbital period of the companion stars and the velocity of the stellar wind. The mixed pulsar-stellar wind expands with a specific velocity determined by the pulsar power and the mass loss rate of the companion star. Relativistic particles, either from the inner pulsar magnetosphere and/or accelerated at the shocks between stellar and pulsar winds, are expected to be captured and isotropized in the reference frame of the mixed wind. Therefore, they can efficiently Comptonize stellar radiation producing GeV-TeV γ-rays in the inverse Compton process. We calculate the γ-ray spectra expected in such scenario for the two example binary systems: J1816+4510 which is the Redback-type millisecond binary and LS 5039 which is supposed to contain energetic pulsar. It is concluded that the steady TeV γ-ray emission from J1816+4510 should be on the 100 h sensitivity limit of the planned Cherenkov Telescope Array, provided that ∼ 10 per cent of the rotational energy lost by the pulsar is transferred to TeV electrons. On the other hand, the comparison of the predicted steady TeV γ-ray emission, expected from γ-ray binary LS 5039, with the observations of the TeV emission in a low state, reported by the High Energy Stereoscopic System Collaboration, allows us to put stringent upper limit on the product of the part of the hemisphere in which the mixed pulsar-stellar wind is confined, Δmix, and the energy conversion efficiency, , from the supposed pulsar to the TeV electrons injected in this system, Δmix  < 1 per cent. This lower limit can be understood provided that either the acceleration efficiency of electrons is rather low ( ∼ 1 per cent), or the parameters of the stellar wind from the companion star are less extreme than expected, or the injection/acceleration process of electrons occurs highly anisotropically with the predominance towards the companion star.