the selected data and measured the burst oscillation amplitude and phase. We then repeated this method for the non-burst data. The resulting amplitude spectra are shown in Figure \[fig:bo-spectrum\]. Although the averaged profiles are similar, the energy dependence of the burst oscillation is very different from that of the pulsar. Particularly notable is that the burst oscillation amplitude is mostly constant below $\approx5$keV, but rises sharply at $6-7$keV. ]{}

![ Waveform of the burst oscillation observed in [SAX J1808]{}, compared to the waveform of the accretion-powered pulsation as seen outside the X-ray burst interval. []{data-label="fig:bo"}](bo-waveform.pdf){width="\linewidth"}

![ Top: energy dependence of the burst oscillation waveform. Bottom: same for the persistent pulsation observed outside the X-ray burst interval. Note that these data were computed using a sliding window, so adjacent points are correlated. Additionally, in order to look for decohering noise, we plot the waveform phase even if the amplitude is not formally significant. See text for further details. []{data-label="fig:bo-spectrum"}](dynamic-energy-spectra.pdf){width="\linewidth"}

Discussion {#sec:discussion}
==========

We detected a bright X-ray burst from [SAX J1808]{}with [*NICER*]{}. The burst showed a peculiar light curve, with a notable pause during the rise and a double-peaked structure. Additionally, we detected significant burst oscillations in the cooling tail of 