Superhump period of the black hole X-ray binary GX 339-4

We investigate variability of optical and near-infrared light curves of the X-ray binary GX 339-4 on a timescale of days. We use the data in four filters from six intervals corresponding to the soft state and from four intervals corresponding to the quiescent state. In the soft state, we find prominent oscillations with the average period P = 1.772 $\pm$ 0.003 d, which is offset from the measured orbital period of the system by 0.7 per cent. We suggest that the measured periodicity originates from the superhumps. In line with this interpretation we find no periodicity in the quiescent state. The obtained period excess $\epsilon$ is below typical values found for cataclysmic variables for the same mass ratio of the binary. We discuss implications of this finding in the context of the superhump theory.