Best-fitting peak energies of the PFS features and energies of the fundamental cyclotron line for the different observations. We report the cyclotron line energies from the spectral analysis of Doroshenko et al. (2017) (grey dots) and from this work (black dots). Red, blue and green points sign the best-fitting values from the PFS features, when two lines are clearly identified (red and blue dots) and when only one peak has been detected (green dots) (from Tables 2 and 3).