Extended Data Fig. 1: Subpulse frequency drift rates.

a, b, Subpulse model fits for the 17 September CHIME/FRB burst (a) and the 28 October CHIME/Pulsar burst (b). Left to right, the lower subpanel shows dedispersed intensity data (DM = 189.4 pc cm⁻³), the best-fit model and residuals, and the upper subpanel shows the summed time series. Only the half of the receiver bandwidth in which the burst was detected is used in the analysis. The colour scale for the intensity data and residuals is clipped to ±3σ from the median of the residual data and a divergent rather than a sequential colour scale is used for the residuals to guide the eye. Red points overlaid on the models show the centre frequency and 1σ statistical uncertainty with a 10-MHz systematic error added in quadrature. The red dashed lines show linear drift rates of −6.4 MHz ms⁻¹ (a) and −1.3 MHz ms⁻¹ (b).