Exploration of the internal shock parameter space (2). The distribution of the three parameters defining the relative importance of inverse Compton scatterings, Klein-Nishina corrections and adiabatic cooling, Y_th, w_m and Γ_c/Γ_m are plotted for all cases presented in Fig. 6. In addition the distributions of the same parameters for cases where the synchrotron spectrum peaks in the gamma-ray range (10   keV ≤ E_p,obs ≤ 10   MeV) and the low-energy photon index is in the correct range are also plotted (−3/2 ≤ α ≤ −1: red; −1 ≤ α ≤ −2/3: blue).