One-dimensional FLASH simulations. Left panel: time evolution of the position of the forward shock, r_sh (r3, r4, r5), and of its expansion velocity, v_sh (v3, v4, v5). Right panel: time evolution of the thermal energy inside the shock, E_th (Et3, Et4, Et5), and of the kinetic energy of the shock, E_kin (Ek3, Ek4, Ek5). Individual quantities are labeled with the value of the power index of the ISM density n_out = 10³, 10⁴, and 10⁵ cm⁻³.