Gamma-ray burst spectral evolution in the internal shock model: comparison with the observations

Using a time-dependent numerical model in which the prompt gamma-ray burst (GRB) emission is calculated in the framework of the internal shock model on a broad energy range (from soft X-ray to GeV energies), we compute GRB lightcurves and time-evolving spectra. We show how the spectral evolution in this model is determined by the evolution of the physical conditions in the shocked regions and by the dominant radiative process for the effective microphysics parameters. The predictions of a model are confronted by the observations in the standard sub-MeV energy range, as well as with high energy bands observed by Fermi.