Observer-frame H-band (purple) and X-ray (black) light curves. Solid lines show the joint fit with a smoothly-broken power-law, assuming common achromatic breaks. The dashed line shows the H-band light curve without constant component. The horizontal dotted line shows the modelled H-band constant component. Following the slow-cooling scenario (Sect. 3.3), we fixed the pre-break decay indices to α_opt = 0.9 and α_X = 1.15. The last break is interpreted as a jet break, and thus the post-break decay index has been fixed to α_opt, X = p = 2.2. The late flattening in the H-band light curve can be explained by a constant contribution from a host or intervening system. See Sect. 3.5 for details.