Mock images of the simulated ORC at t = 73 Myr. Left and centre: Synchrotron flux density at four frequencies (indicated in the top-left corner of each panel). The images are smoothed with a Gaussian kernel length matching the respective resolution of the telescope, shown in the bottom of each panel. Right: Spectral index derived from the two left panels. We applied a circular mask in these images to highlight the circular shape, where its extent is indicated by the dashed line in the upper left panel.