Fourier analysis of the X-ray lightcurves of λ Cep in June and August 2013. The top three panels show the power spectra for the three EPIC instruments whilst the bottom panel displays the power spectral window of the EPIC-pn time series. MOS1 and MOS2 have very similar spectral windows. The dashed vertical lines indicate the frequencies ν₁ = 1.315, ν₂ = 0.245 and ν₃ = 0.495 d^-1 found in the analysis of our optical spectra.