(a) XRISM Xtend light curve in the 0.5–10 keV band, showing the temporal evolution of the X-ray flux. (b) Power spectral density (PSD) derived from the light curve, exhibiting a significant peak at approximately 1.2 × 10⁻⁵ Hz. The solid blue line represents the best-fit model (red noise plus Poisson noise), and the dashed red line indicates the global 95% confidence level. The detection of the peak above this threshold confirms its statistical significance against the underlying red-noise continuum.