Non-pulsed gamma radiation from binary system with a pulsar

Abstract

Consider binary system with a millisecond pulsar ejecting relativistic particles and an optical star emitting soft photons with the energy $\omega \simeq 1-10$ eV. These low-energy photons are scattered by the relativistic electrons and positrons of the pulsar's wind. The scattered photons forms a wide spectrum from hard X-ray band up to gamma band $\epsilon \simeq 1-1000$GeV >.When the pulsar wind is isotropic the luminosity of gamma radiation $L_\gamma =L_\gamma (\psi)$ depends heavily on the angle $\psi $ between the directions to the optical star and to the observer from the pulsar. During the orbital motion this angle varies periodically giving rise to the periodical change of the observed intensity of the gamma radiation and its spectrum. We calculated the spectral shape of the scattered hard photons. Under the assumption that the energy losses of the relativistic particles are small we receive analytical formulas. We apply our results to the binary system PSR B1259-63 and show that if the wind from the Be star is accounted for then it is possible to reproduce the observed spectrum.