a) Contours of 17 GHz (NoRH, 04:04) flare sources (black solid: Stokes I, 50%, 70%, 90% of the maximum; white solid: Stokes V, RCP, 70%, 90% of the maximum; white dotted: Stokes V, LCP, 70%, 90% of the minimum) superimposed on an MDI magnetogram (04:48:01.61, light areas represent N-polarity, dark areas show S-polarity). The axes show hereafter arc seconds from the solar disk center; b) enlarged flare site denoted in panel a) by the broken frame. Contours of 17 GHz (NoRH, 04:03:40) Contours levels are the same. Black thick contours correspond to the HXR source (Yohkoh/HXT/H; 04:03:40.25; 20%, 50%, 80% of the maximum). Thin solid grey contours mark N-polarity [levels 600, 800 G], and thin white contours mark S-polarity [levels  − 600,  − 500 G].