APPARENT SUPERLUMINAL EXPANSION IN CYGNUS-X-3

The Galactic radio-emitting X-ray binary Cygnus X-3 is known to be a s ource of large-scale radio jets associated with periods of intense rad io flaring. These jets have. been found to have an expansion velocity of similar to 0.3c and are believed (on kinematic grounds) to lie clos e to the plane of the sky. We present new observations of Cygnus X-3 u sing the VLBA. at 15 GHz. These observations, which included the detec tion of two small flares, show an additional kind of behaviour with ap parent superluminal expansion along both major and minor axes. Evidenc e for superluminal activity has been found in a number of X-ray binary systems such as GRS 1915 + 105 and GRO J1655 - 40 with their superlum inal radio jets. Apparently similar morphologies of the Galactic and e xtragalactic jet sources have led to the X-ray binaries being describe d as 'micro-quasars'. The superluminal expansion seen in our results a ppears to be different in nature from these other two sources, and a n umber of mechanisms are presented and discussed.