Shock geometry and inverse compton emission from the wind of a binary pulsar

PSR B1259-63 is a 47 ms radio pulsar with a high spin-down luminosity which is in a close, highly eccentric 3.5 yr orbit about a bright stellar compan ion. The binary system may be a detectable source of hard gamma -rays produ ced by inverse Compton scattering of photons from the B2e star SS2883 by el ectrons and positrons in the pulsar wind. The star provides an enormous den sity of optical photons in the vicinity of the pulsar. particularly at epoc hs near periastron. We calculate the emission from the unshocked region of the pulsar wind. assuming that it terminates at a shock where it attains pr essure balance with the companion's wind. The spectra and light curves for the inverse Compton emission from the shock-terminated wind are compared wi th those for an unterminated wind. If the pulsar's wind is weaker than that from the companion star. the termination of the wind decreases the inverse Compton flux, particularly near periastron. The termination shock geometry has the effect of decreasing the asymmetry of the gamma -ray light curve a round periastron. which arises because of the asymmetrical variation of the scattering angle.