Bayesian posterior probability density vs. frequencies in the time interval of 259–267 s from the giant flare onset. Dashed vertical lines indicate the 68% region of the highest probability density. Odds ratio of periodic vs. constant model is  ~200. The right panel depicts the phase-folded light curve with frequency f_QPO = 16.88   Hz, with an almost perfect sinusoidal shape (for details, see text).