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Cygnus X-3A luminous X-ray binary source with an unusually short (4.8 hour) binary period. The short period suggests that the system consists of a neutron star and a low-mass companion. Recent infrared spectra show strong helium emission lines as for a Wolf-Rayet companion star. The sinusoidal X-ray light curve is interpreted as being due to scattering of X-rays from the (unseen) central source by a hot dense wind driven off the companion star. Cygnus X-3 occasionally produces strong sometimes violent radio flares, first observed in 1972, between which it shows variable radio emission with a dominant component having a periodicity of 4.8 hours, similar to the X-ray period. Extremely high energy (>1015 eV) gamma rays have also been detected, though not recently. These observations make Cygnus X-3 a unique source. It is postulated that the unusual properties may arise from very rapid rotation of the neutron star embedded in the dense wind of its companion star.
Cygnus X-3[′sig·nəs ‚eks ′thrē]
A variable source of x-rays, with a period of 4.8 hours, associated with a variable radio source that flared up to enormous levels in September 1972 with no observed increase in x-ray emission. Abbreviated Cyg X-3.