PDSs of 4U 0115+63 normalized as in Leahy et al. (1983) and obtained using 0.1 s binned, background-subtracted light curves. The gray step line represents the PDS from Obs3, which clearly shows a red noise component at low frequencies. The red step line corresponds to the PDS from the combined light curves of Obs1, Obs2, and Obs2016, which exhibits a flat (white noise) distribution in the 0.003−1 Hz range. The inset provides a zoomed-in view around the NS spin frequency (highlighted by the green stripe).