Calibration with an improved sky model. This shows the difference between the 8-band residual maps (2003 observation) produced with the original and the improved sky models. Structures around 3C 147 itself and the off-axis sources are mostly due to “selfcal contamination” in the original model caused by incorrect off-axis source positions. These are well within the noise: the intensity range of this image is  ± 2   μJy, while the 8-band maps have a thermal noise of 13.5   μJy.