Light curves of GRB 130603B at X-ray (top) and optical (bottom) wavelengths. Detections are indicated with dots and upper limits (3σ) with arrows. The optical photometry of the different bands has been scaled to the r-band. The vertical lines indicate the times when spectra were obtained. We include optical data from the literature (Cucchiara et al. 2013a; Tanvir et al. 2013). The red lines are fits of the light curves with broken power laws, which show that, while the evolution of X-rays and optical are very different until 0.3 days, their evolution is consistent after that time. The dashed blue line is the expected r-band light curve of a supernova like SN 1998bw, the most common template for long GRBs, after including an extinction of A_V = 0.86 mag. The most constraining limits indicate that any supernova contribution would be at least 100 times dimmer than SN 1998bw in the r-band, once corrected of extinction (blue dotted line). However, see Tanvir et al. (2013) and Berger et al. (2013a) for the detection of a “kilonova” component at infrared wavelengths.