Distribution of the slope p of the nonthermal population of accelerated particles for the sample of 22 GRBs analyzed in this work. This distribution has been derived from the β distribution shown in Fig. 4, by using the relation p = −2 − 2β or, equivalently, p = 2β_e (i.e., assuming synchrotron emission in the fast cooling regime). The median value of p along with its error bar on p values are represented with the black dot and solid line, respectively. For comparison, the distribution of p derived for the Fermi/GBM catalog bursts under the same assumption is also plotted (red dashed histogram).