Wavelet power spectrum for the detrended light curve of the impulsive phase of HXR emission. The time range used is the same as in Fig. 2. The dotted grey curve in the top panel is the original light curve prior to detrending. The bottom panel shows the wavelet power spectrum, which has enhanced power above the 95% significance level (the dashed white curve) during the early impulsive phase. The global wavelet is also shown on the right-hand side. The enhanced power is at a period of ∼10 s, which agrees well with the 7 s period derived from the Gaussian decomposition method in Collier et al. (2023).