EXOSAT MEDA observations of Cygnus X-3.

Abstract

Results of a continuous 30.6-hr X-ray observation of Cygnus X-3 with a large area detector are presented. These show the well known, roughly sinusoidal light curve at the 4.8-hr period, with a phase-dependent variability at short time-scales, and associated spectral behavior. The sinusoidal modulation is interpreted as due to electron scattering in a wind from the neutron star's companion. The motion of the neutron star creates a cavity in the wind which is swept clear by radiation pressure and distorts the light curve in a systematic way. The parameters required by this picture strongly suggest that the wind is generated by X-ray heating of the companion, offering a natural explanation for the fact that the wind has a scattering optical depth of order unity. The model can also account for variations in the iron line, a hard X-ray component and quiescent radio emission (by nonthermal processes in the wind) and a soft X-ray component (thermal emission from the wind).