a) GMRT 327 MHz contours of the radio halo (black and white; same as Fig. 1b), overlaid on the VLA 1.4 GHz image at the resolution of 42′′ × 37′′, obtained from the re-processed NVSS data. The rms noise in the 1.4 GHz image is 0.25 mJy beam^-1. Point sources, derived from an image produced with only baselines  ≥ 2 kλ, have been subtracted out at 1.4 GHz. b) Same re-processed NVSS image as panel a), with 1.4 GHz contours overlaid at levels − 0.5 (dashed black), 0.5, 0.75 and 1 (white) mJy beam^-1.