Modeling Orbital Modulation of Cyg X-3 by Particle Simulations

ABSTRACT The formation of the circumbinary envelope of Cygnus X-3 was studied by particle simulations of the WR (Wolf Rayet) -companion wind. Light curves resulting from electron scattering absorption in this envelope were computed and compared with observed IBIS/ISGRI and BATSE light curves. For reasonable values of binary parameters (masses, inclination) and wind velocities, a stable envelope was formed during a few binary orbits. Assuming approximately 10 -6 solar mass/year for the rate of the WR-wind, the observed light curves and accretion luminosity can be re-produced (assuming Thomson scattering opacity in the ionized He-rich envelope). The illuminated envelope can also model the observed - Chandraspectrum using the photoionizing XSTAR-code. Furthermore, we discuss observed radial velocity curves of IR emission lines in the context of simulated velocity fields and find good agreement. Ψ 1. INTRODUCTION Cygnus X-3 is a close binary star with an orbital period of 4.8 hours. The donor star is probably a Wolf Rayet-star of WNE-type ([2,5]) whose wind feeds the accretion luminosity 10