  In observations with the Australia Telescope Compact Array we have resolved
the radio counterpart of the unusual X-ray binary Cir X-1 into an asymmetric
extended structure on arcsecond scales. In order to quantify the asymmetry we
have redetermined as accurately as possible both the optical and radio
coordinates of the source. The extended emission can be understood as a
compact, absorbed core at the location of the X-ray binary, and extended
emission up to 2 arcsec to the southeast of the core. The arcsec-scale extended
emission aligns with the larger, more symmetric arcmin-scale collimated
structures in the surrounding synchrotron nebula. This suggests that the
transport of mass and/or energy from the X-ray binary to the synchroton nebula
is occurring via the arcsec-scale structures. The ratio of extended flux from
the southeast to that from the northwest of the core is at least 2:1.
Interpreted as relativistic aberration of an intrinsically symmetric jet from
the source, this implies a minimum outflow velocity of 0.1 c. Alternatively,
the emission may be intrinsically asymmetric, perhaps as a result of the high
space velocity of the system.
