A one-sided highly relativistic jet from Cygnus X-3

Very Long Baseline Array images of the X-ray binary Cygnus X-3 were obtained 2, 4, and 7 days after the peak of a 10 Jy flare on 1997 February 4. The first two images show a curved one-sided jet, and the third shows a scatter-broadened disk, presumably at the position of the core. The jet curvature changes from the first to the second epoch, which strongly suggests a precessing jet. The ratio of the flux density in the approaching jet to that in the (undetected) receding jet is greater than or similar to 330; if this asymmetry is due to Doppler boosting, the implied jet speed is greater than or similar to0.81c. Precessing-jet model fits, together with the assumption that the jet is intrinsically symmetric and was ejected during or after the major flare, yield the following constraints : the jet inclination to the line of sight must be less than or similar to 14 degrees, the cone opening angle must be less than or similar to 12 degrees, and the precession period must be greater than or similar to 60 days.