Best fit parameters resulting from the spectral analysis of the full sample. Left-hand panels: photon indices. Right-hand panels: peak and break energies. Top left: distribution of α₁ (red) and β₂ (green), representing the indices below and above the break energy. Bottom left: α₁ vs. α₂ (circles) and α vs. β for GRBs with a spectrum modeled by a Band function with second index < −2 (squares). In both left-hand panels, the values for α₁ and α₂ predicted from fast cooling synchrotron emission are drawn as dashed lines. In the bottom panel they should be used as reference lines for the circle symbols only. Top right: E_peak (blue) and E_break (red) distributions. Bottom right: E_peak vs. E_break for spectra where both features can be constrained (Bandcut model). Circles refer to the observer frame, while stars are used for the rest frame, for those GRBs with measured redshift. The positions before and after cosmological redshift correction are connected with a solid line.