Case C: an example of a pulse generated by an internal shock with synchrotron radiation in “marginally fast cooling”. Same as in Figs. 8 and 9. The slope α is steeper (−1 < α < −2/3 for the whole duration) than in case A and B, due to a higher ratio Γ_c/Γ_m. This ratio is of the order of 0.1−1 at the peak of the pulse (“marginally fast cooling”), and even larger in the tail (slow cooling).