Left panel shows energy dependent time-lag spectra at ∼2.55 Hz fundamental QPO frequency (black circles) and 5.08 Hz harmonic frequency (red circles) respectively. While soft lag is observed at QPO frequency, the lag spectra clearly show hard lag at harmonic frequency. The middle panel shows phase-lag spectra as a function of Fourier frequency, where the phase lag is computed between 3.0–5.0 keV and 10.0–20.0 keV energy bands. The position of ∼2.55 Hz QPO and its harmonic at ∼5.03 Hz are shown by vertical dotted lines. Clearly, a phase rotation from negative at QPO frequency to positive at harmonic frequency is visible. The right panel shows fractional rms spectra at the fundamental QPO frequency (black) and its harmonic (red).