Summary plots of the GRBs from Sample 2. In this case, for at least one temporal bin, the optical flux is above f_M, opt, indicating that optical and X-ray data are not compatible with a single synchrotron spectrum. The symbols are the same as in Fig. 2, and we indicate the temporal bin where f_opt > f_M, opt with a vertical light blue band. In the bottom panel, we show the X-ray spectral index for each temporal bin with black error bars, while the dot-dashed line is the time-averaged value. In the same sub-plot, we also report the optical spectral index with an orange line (the yellow band is the uncertainty interval). (a) 050730, (b) 060614, (c) 080310, (d) 081007.