Panel a: maximum burst duration in minutes through our observing band (120–168 MHz) as a function of coronal temperature and base wind density, modelled with an iso-thermal Parker wind model. White contour lines show the observed durations of bursts B20 and B21. Regions above the contours can produce bursts with the observed durations, with CME shock speeds exceeding the wind- and Alfvén speed. Panel b: CME shock speeds that exactly produce burst B20’s observed duration of 0.988 minutes, as a function of coronal temperature and base wind density, modelled with an isothermal Parker wind model. The black line marks the minimum shock speed exceeding both the Alfvén and wind speeds. Solutions exist for shock speeds upwards of ~1000 km s⁻¹. Panel c: CME shock speeds that exactly produce burst B21’s observed duration of 13.334 minutes, as a function of coronal temperature and base wind density, modelled with an isothermal Parker wind model. The black line marks the minimum shock speed exceeding both the Alfvén and wind speeds. Solutions exist for shock speeds upwards of ~300 km s⁻¹.