Illustrations of the superposition effect on the spectral shape for the simulated GRB 081224. These three mock spectra correspond to that of the onset time bin of the second pulse of the mock GRB as shown in Figure  6. Every mock spectrum in the onset time bin of the second pulse of the mock GRB (solid dots) is roughly the superimposition of the observed GRB 081224 spectra in the two different time bins as marked in the legends.