(Top panel) Comparison of the fluxed X-ray light curve at 10 keV; (middle panel) the GROND J (yellow), H (blue), K_s (green) bands; (bottom panel) the photon index of the X-ray spectrum (black, left y-axis scale) and the residuals of the model fit (see text) to the GROND JHK data (colour as in the middle panel, right y-axis scale). The diagonal-hatched region denotes epoch 1, the cross-hatched regions epoch 2. The dashed vertical lines mark the maxima in the photon spectral index Γ (Γ = β + 1) to guide the eyes.