1999MNRAS.304..359C

We consider a binary system with a millisecond pulsar ejecting relativistic particles and an optical star emitting soft photons with energy ω ≃ 1–10 eV. These low-energy photons are scattered by the relativistic electrons and positrons of the pulsar wind. The scattered photons form a wide spectrum from the hard X-ray band up to gamma band ε ≃ 1–1000 GeV.

When the pulsar wind is isotropic, the luminosity of gamma radiation L_γ=L_γ(ψ) depends strongly on the angle ψ between the directions to the optical star and the observer from the pulsar. During the orbital motion this angle varies periodically, giving rise to a periodic change of the observed intensity of the gamma radiation and its spectrum. We calculate the spectral shape of the scattered hard photons. Under the assumption that the energy losses of the relativistic particles are small, we derive analytic formulae for the spectra of the photons. 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.