Dynamic spectrum and source location during the high-frequency burst group 12:17–12:21 UT. (a) ORFEES dynamic spectrum using 0.1 s time resolution (top panel; grey levels graded from 0.99 to 1.5 times the pre-event background, logarithmic scale), and the corresponding 1D images at three frequencies (NRH, 0.25 s integration). The overplotted red line marks the peak positions of the first moving type IV source (NRH, 10 s integration). (b) Map of the burst at 12:19:04 UT (iso-intensity contour at half-maximum at 408 MHz overplotted on the simultaneous image at 432 MHz; 0.25 s integration).