Phase lags of the main peak in normalized phase units (points) and linear correlation coefficients (stars) as a function of energy. We considered here BeppoSAX data from the MECS (2–8.5 keV), the HPGSPC (8.5–25 keV), and the PDS (>25 keV). RXTE data are from the PCA (3–45 keV) and the HEXTE-B (>45 keV). The correlation function is computed on a phase interval of 0.4 phase units, centered on the maximum of the reference pulse profiles. The solid line represents the best-fit function to the phase lags (see text for the details).