Quenching of the radio jet during the X-ray high state of GX 339-4

We have observed the black hole candidate X-ray binary GX 339-4 at radio wa velengths before, during, and after the 1998 high/soft X-ray state transiti on. We find that the radio emission from the system is strongly correlated with the hard X-ray emission and is reduced by a factor of greater than or equal to 25 during the high/soft state compared with the more usual low/har d state. At the points of state transition, we note brief periods of unusua lly optically thin radio emission that may correspond to discrete ejection events. We propose that in the low/hard state, black hole X-ray binaries pr oduce a quasi-continuous outflow, that in the high/soft state, this outflow is suppressed, and that state transitions often result in one or more disc rete ejection events. Future models for low/hard states, such as advection- dominated solutions, need to take into account the strong outflow of relati vistic electrons from the system. We propose that the inferred Comptonizing corona and the base of the jetlike outflow are the same thing, based on th e strong correlation between radio and hard X-ray emission in GX 339-4 and other X-ray binaries and on the similarity in inferred location and composi tion of these two components.