• accretion, accretion discs;
  • binaries: general;
  • ISM: jets and outflows;
  • radio continuum: stars;
  • X-rays: stars;
  • X-rays: individual: GX 339−4


We report on the formation and evolution of a large-scale, synchrotron-emitting jet from the black hole candidate and X-ray binary system GX 339−4. In 2002 May, the source moved from a low/hard to a very high X-ray state, contemporaneously exhibiting a very bright optically thin radio flare. Further observations with the Australia Telescope Compact Array have tracked the formation of a collimated structure extending to about 12 arcsec, with apparent velocity greater than 0.9c. The luminosity of the outflow seems to be rapidly decreasing; these observations confirm that transient large-scale jets are likely to be common events triggered by X-ray state transitions in black hole X-ray binaries.