Left panel: spatiotemporal evolution of the BB + HB emission at 150.9, 173.2, and 228.0 MHz. Different symbols and colors specify, respectively, the frequencies and times t_k at which the HBs were observed. HBs have been imaged at the H frequency: Only the position of the maximum temperature brightness (T_B, max) is depicted. Solid circles at times t₂ and t₃ indicate the observed positions of the BB emission; dotted circles at times t₁, t₄, and t₅ denote inferred positions of the BB emission on the basis of the observed HB emissions. Dashed arrows departing from solid and dotted circles identify the directions of the electron beams producing the observed HB emission at each time t_k. The bottom panel of the inset shows a simplified overview of the observed HB structure in the time interval 10:14−10:19 UT, while the upper panel shows the maximum T_B at each frequency. Right panel: coronal magnetic field reconstructed with the PFSS technique up to 1.25 R_⊙. White lines correspond to closed magnetic field loops, red lines to open fields. The observed radio sources are aligned along open field lines. The plot was obtained with the JHelioviewer tool (Müller et al. 2017).