[see, e.g., @Bilous2019 and references therein]. Specifically, we used window sizes of $T=1,2,{\rm~and~} 4{{\rm\,s}\xspace}$, with strides of $T/10{{\rm\,s}\xspace}$. For each window position, we computed a power spectrum and searched for a signal power in excess of the expected noise distribution [@Klis1989]. We detected a significant oscillation ($>3\sigma$) in all windows between $t=17.7{{\rm\,s}\xspace}$ and $t=24.6{{\rm\,s}\xspace}$. The fractional sinusoidal amplitude[^2] of the burst oscillation was $(4.0\pm0.6)\%$, while the oscillation frequency was $401$Hz and did not show any significant drift.

Given the stability of the burst oscillation frequency, we folded the event times within the noted epoch on the pulsar spin period to obtain a waveform for the burst oscillation. For comparison, we also extracted the waveform of the persistent pulsations from the full ObsID, excluding the burst emission (see @ATelBult19c for a preliminary ephemeris). Both waveforms are shown in Figure \[fig:bo\]. The burst oscillation has a similar profile and amplitude as the persistent pulsation, but appears to lead the pulse by $34\arcdeg\pm7\arcdeg$.

[ To resolve the burst oscillation with respect to photon energy, we applied a sliding window to the instrument energy channel space, using a window size of 100 channels and strides of 10 channels. At each window position, we folded 