Slices through our fiducial Mach 3 simulation at t = 180 Myr showing: (i) time since injection, (ii) CR electron number density at p = 2 × 10⁴ (see text), (iii) magnetic field strength, and (iv) synchrotron emissivity at 150 MHz. Only tracers that have undergone DSA are shown. A Rayleigh-Taylor instability induces a counter-streaming plume (in the shock rest frame) that brings aged, and therefore cooled, electrons close to the shock front. However, these electrons are still relatively bright at 150 MHz due to magnetic field amplification up to μG levels. An animated version of this figure can be found here.