Temporal decay index α_norm vs. spectral index β_norm of Type 0 (red squares), of the second segment of Type Ia (blue triangles), and the third segment of Type II (green stars) light curves of the present sample. Grey symbols refer to the sample of Margutti et al. (2011). The shaded areas correspond to the expectations of the standard afterglow models in the slow cooling regime: the lower area only is for ISM model, the intermediate area plus the lower area are for the wind model (see e.g. Table 2 in Zhang et al. 2006), the upper area is for the post jet-break (Sari et al. 1999).