3D Mach number distribution at the shock cells at selected simulation times (top). Standard deviation of the Mach number PDF as function of time (bottom). Each column corresponds to the different initial Mach number of the shock. For the 2D Mach number distribution we used different weights for the projection (see legend). Note: here, I_ν is taken from the fresh-injection model (case ℳ_cr = 1; see Sect. 4.2). See Appendix C for a comparison between weights corresponding to the emission coming from the fresh-injection and re-acceleration models.