Birthplaces of X-ray emission lines in Cygnus X-3
Abstract
We investigate the formation of X-ray emission lines in the wind of the Wolf-Rayet (WR) companion in Cyg X-3 by analyzing their orbital dynamics using Chandra High Energy Transmission Grating (HEG) observations during a hypersoft state. Our goal is to constrain the X-ray transparency of the recently discovered funnel-like structure surrounding the compact star, as revealed by X-ray polarimetry. All lines exhibit sinusoidal orbital modulation, with the velocity amplitude generally increasing and the orbital phase with the highest blueshift generally decreasing for ions with a higher ionisation potential. The Fexxvi-line displays velocity extremes at phase 0.25 (blueshift) and 0.75 (redshift), indicating that the line-emitting region is close to the compact component (disc or corona) and thus reflects the orbital motion. The Fexxv-line shows a complex behaviour that cannot be fully resolved with the Chandra/HEG resolution. Other lines display velocity extremes scattered around phase 0.5 (blueshift) and 0.0 (redshift), with velocity amplitudes of 100--300 km/s, suggesting their origin in the WR stellar wind between the two components along 3D -surfaces. Parts of the emission lines of Arxviii and Caxx originated around the compact star (disc or corona). The recent polarisation funnel-modelling is consistent with the present results during the hypersoft state.
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