Extended Data Fig. 5: Lomb–Scargle periodogram of the ULTRASPEC flares.

Each panel shows the periodogram for the flare itself, for a region of the light curve with no notable detections (‘noise’) and for the full light curve (‘all’). Horizontal dashed lines mark the power expected for a false-alarm peak (with false-alarm probability 2.5%) under the assumption that there is no periodicity present in the data, using a bootstrap simulation. The only peaks higher than this threshold are from the cadence of the observation (30 s, and an alias at half that value), from the overall flare width and from the duration of the observation.