  We report the results of a long-term campaign of radio, soft- and hard- X-ray
observations of the galactic black hole candidate GX 339-4. In the Low-Hard
X-ray state the system displays a strong 3-way linear correlation between soft-
and hard-X-rays and radio emission, implying a coupling between the
Comptonising corona and a radio-emitting compact jet. In this state the radio
emission is linearly polarised at a level of around 2 %, with an almost
constant polarisation angle, indicative of a favored axis in this system
probably related to the compact jet and/or black hole spin axis. In the Off
X-ray state the radio emission declines with the X-ray emission to below
detectable levels, suggesting that it is simply a lower-luminosity version of
the Low-Hard state. In the High-Soft state both the hard-X-ray and radio
emission are suppressed. We also note that the transitions from the Low-Hard
state to the High-Soft state (and the reverse) are possibly associated with
discrete ejection(s) of expanding relativistic plasma.
