Histograms of strongest periodicities visible in Lomb-Scargle periodograms. Only periodicities exceeding the significance level FIP = 0.01 were taken into account. In the case of four flares for which different averaging times or time intervals were used, two periodicities were obtained; both are included in the histogram. In panel (a), the strongest periodicity for each flare corresponds to the highest peak in the Lomb-Scargle periodogram, regardless of the energy channel. Panels (b), (c), and (d) correspond to the energy channel 4–10, 10–15, and 15–25 keV, respectively. The histograms include 95, 70, 77, and 58 flares, respectively.