Spectral curvature map of the halo in MACS J0717.5+3745 at 8″ resolution. Left: four frequency spectral curvature map between 144 MHz and 5.5 GHz. The SC is negative for a convex spectrum. From the curvature map it is evident that the halo shows a clear curvature. There are also significant local variations in the curvature. Right: corresponding uncertainty between 1.5 and 5.5 GHz. Contour levels are drawn at [1, 2, 4, 8, …] × 4σ_rms, and are from the VLA L-band image.