Cygnus A – total intensity and spectral-index: this figure shows the MS-MFS total intensity map (top), and spectral-index maps obtained via three methods – MS-MFS (second row), a hybrid single-band method (third row), and from high-resolution full-synthesis narrow-band images at 1.4 and 4.8 GHz (bottom). The MS-MFS spectral index map has the angular-resolution of the total intensity map, and agrees with the values in the high-resolution comparison map (α =  −0.5 at the hotspots increasing to α ≈  − 1.0 in the halo). However, the hybrid method resulted in a map with a wider range of values (positive and negative) and is at a much lower angular resolution.