Cygnus X-3 light-curve model in the TeV energy region

Abstract

We consider a close binary system containing a compact object and suggest that very high-energy (VHE) γ-rays are produced near this object. In such a system the VHE γ-rays have to interact with soft photons around the companion star by γγ→ee reactions. These soft photons have a radial distribution, so the VHE γ-rays will reach the observer when their source lies between the companion star and the observer, because the reaction is impossible if the angle between the momenta of soft photon and γ-quantum is small. In this model the VHE γ-ray light curve has a sharp maximum at the orbital phase region 0.2–0.8 for orbits with various orientations and eccentricities. Our calculations show that for the orbital parameters of Cygnus X–3 the light-curve maximum occurs at phase ≈ 0.6, which is in agreement with recent experimental data.