Results from Hybrid MHD-Lagrangian simulations. Top panel: visualisation of synchrotron emissivity at 880 MHz (in code units). Bottom panels: phase plot of the spectral index computed between 880 MHz and 1.2 GHz versus surface brightness at 880 MHz. We show the values at selected pixels in the surface brightness maps. Upper (lower) panel: values corresponding to the shock front (downstream) region. We obtain magnetic field maps by projecting the 3D magnetic field using the 880 MHz emissivity as a weight, and finally, we colour-code each point in the plot with its corresponding weighted magnetic field value. The arrow shows a group of brighter particles associated with stronger magnetic fields. See Fig. 27 for a comparison with real data.