  A recent detection of the peculiar neutron star X-ray binary Circinus X-1
with electronic very long baseline interferometry (e-VLBI) prompted the
suggestion that compact, non-variable radio emission persists through the
entire 16.6-day orbit of the binary system. We present the results of a high
angular resolution monitoring campaign conducted with the Australian Long
Baseline Array in real-time e-VLBI mode. e-VLBI observations of Circinus X-1
were made on alternate days over a period of 20 days covering the full binary
orbit. A compact radio source associated with Circinus X-1 was clearly detected
at orbital phases following periastron passage but no compact radio emission
was detected at any other orbital phase, ruling out the presence of a
persistent, compact emitting region at our sensitivity levels. The jet was not
resolved at any epoch of our 1.4-GHz monitoring campaign, suggesting that the
ultrarelativistic flow previously inferred to exist in this source is likely to
be dark. We discuss these findings within the context of previous radio
monitoring of Circinus X-1.
