Case B: an example of a pulse generated by an internal shock with synchrotron radiation in fast cooling regime affected by non negligible inverse Compton scatterings in Klein-Nishina regime. Same as in Fig. 8. The slope α is steeper (−3/2 < α < −1 for the whole duration) than in case A, due to comparable values of w_m but higher values of Y_Th (see the theoretical interpretation in Sect. 3).