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GX 339−4 has been one of the key sources for unravelling the accretion ejection coupling in accreting stellar mass black holes. After a long period of quiescence between 1999 and 2002, GX 339−4 underwent a series of four outbursts that have been intensively observed by many ground‐based observatories [radio/infrared (IR)/optical] and satellites (X‐rays). Here, we present results of these broad‐band observational campaigns, focusing on the optical–IR (OIR)/X‐ray flux correlations over the four outbursts. We found tight OIR/X‐ray correlations over four decades with the presence of a break in the IR/X‐ray correlation in the hard state. This correlation is the same for all four outbursts. This can be interpreted in a consistent way by considering a synchrotron self‐Compton origin of the X‐rays in which the break frequency varies between the optically thick and thin regime of the jet spectrum. We also highlight the similarities and differences between optical/X‐ray and IR/X‐ray correlations which suggest a jet origin of the near‐IR emission in the hard state while the optical is more likely dominated by the blackbody emission of the accretion disc in both hard and soft state. However, we find a non‐negligible contribution of 40 per cent of the jet emission in the  V  band during the hard state. We finally concentrate on a soft‐to‐hard state transition during the decay of the 2004 outburst by comparing the radio, IR, optical and hard X‐rays light curves. It appears that unusual delays between the peak of emission in the different energy domains may provide some important constraints on jet formation scenario.

The infrared/X‐ray correlation of GX 339−4: probing hard X‐ray emission in accreting black holes