Energy spectral index for the cases of R_A = 10^-4 (upper panel) and R_A = 10^-3 (lower panel). Shown is the energy distribution function at the beginning (black lines) and at the end of the simulation for the cases of single injection (red lines) and continuous particle injection (blue lines). Also shown are the spectral indices obtained from power-law fits (dashed lines) to the simulation data (thin lines). (This figure is available in color in electronic form.)