Extended Data Fig. 6: Very strong red noise during GRB 211211A.

a, Light curve of GRB 211211A from Fermi/GBM in 5-975 keV. As shown in Extended Data Fig. 5, a signal yielding candidate powers exceeding the threshold within 500-549 Hz was observed. The corresponding time interval is marked with a red box. The inset shows a detailed view of this signal, revealing a very bright spike lasting about 1 ms. b, c, d, Light curves in the 5-20 keV range from Fermi/GBM detectors with incident angles less than 60^°. The spike, observed around 14.977 s, was detected only by the NaI detector na (50.03^°) and not by detector n2 (28.37^°). Given the spike’s absence in detector n2 and its predominant contribution in the 5-20 keV range, it was excluded as a hyper flare from GRB 211211A. e, f, g, Groth normalized³⁰ power spectra corresponding to the light curves in b, c, d. The grey shaded area denotes the 0-500 Hz frequency range, while the red shaded area highlights the 500-5,000 Hz region and the threshold power from Extended Data Fig. 5a. The bright spike detected by the detector na produced a series of red noise excesses extending up to 2,000 Hz, leading to the observation of extreme Rayleigh power during the search.