Case A: an example of a pulse generated by an internal shock with synchrotron radiation in pure fast cooling. The top panel plots the evolution of the three main parameters shaping the radiated spectrum (see Sect. 3): w_m, Y_Th and Γ_c/Γ_m. The four other panels show the lightcurves in different energy channels corresponding to the GBM and the LAT on board Fermi. The respective contributions of synchrotron and inverse Compton are also indicated. In the two GBM panels, the evolution of the low-energy slope and peak energy of the soft gamma-ray component is also plotted. In this case, the standard fast cooling synchrotron slope α = −3/2 is found for the whole duration.