NGC 5194. Panel a: RC emission at 151 MHz, as derived from LOFAR HBA observations (Mulcahy et al. 2014). The map has been calibrated with direction-independent phase calibration only. Panel b: RC emission at 145 MHz, obtained from the same data set as panel a but calibrated with direction-dependent phase and amplitude calibration. Both maps are presented with a logarithmic transfer function and have an angular resolution of 20 × 20 arcsec², as indicated by the circle in the bottom left corner.