  Observations of the black hole X-ray binary V404 Cyg with the very long
baseline interferometer HSA (the High Sensitivity Array) have detected the
source at a frequency of 8.4 GHz, providing a source position accurate to 0.3
mas relative to the calibrator source. The observations put an upper limit of
1.3 mas on the source size (5.2 AU at 4 kpc) and a lower limit of 7 x 10^6 K on
its brightness temperature during the normal quiescent state, implying that the
radio emission must be non-thermal, most probably synchrotron radiation,
possibly from a jet. The radio lightcurves show a short flare, with a rise time
of about 30 min, confirming that the source remains active in the quiescent
state.
