Best-fitting CRE advection model with an increasing speed for NGC 4013. Top panel: nonthermal intensities at 150 MHz (LOFAR), middle panel: 1.5 GHz (L-band) data, and bottom panel: nonthermal radio spectral index. In all panels, the solid red line represents the model simulation. The errors are represented by a weighted standard deviation. The best-fitting parameters are listed in Table 11 (SPINNAKER and SPINTERACTIVE are available at: www.github.com/vheesen/Spinnaker).