Distributions of the high-energy slope β (photon index) for the 22 GRBs’ spectra analyzed. The different best-fitting models are represented by different colors (stacked on top of each other), while the black empty histogram represents the total distribution of β values derived from the spectral fits performed in this work. On the top of the distributions it is over-plotted the median value and the mean error on the β parameter for the whole sample. For comparison, the distribution of the β values derived from the Fermi/GBM catalog is represented by the red dashed histogram. The distributions have been normalized to the respective sample size.