tokens: ( 1 ) returned best-fitting parameters of α = 2.29 ± 0.08 and log ( N ) = −7.3 ± 0.1. The total number of degrees of freedom was 10 970. These values along with the measured Whittle statistic are provided in Table 4 . Allowing both N and C to vary between data sets did improve the fit by Δ S = 90, but there was no change to the measured slope. Additionally, allowing the fit to be driven by the low-frequency ‘red-noise slope’ by truncating the PSDs at 10 −4 Hz returns best-fitting parameters that are consistent with those listed in Table 4 . We also fitted equation ( 1 ) to PSDs generated in ‘soft’ and ‘hard’ energy bands (0.3–1 and 1–10 keV, respectively). One may expect to observe differences in the PSD at different energies based on the energy dependence of the rms variability at low and high frequencies, as shown in Fig. 7 . For example, it is clear that larger variations are observed between the slow and fast variations in the soft band compared to the hard. Subsequently, we may expect the soft band to have a steeper PSD. However, we found that the PSD does not exhibit any significant energy-dependence with best-fitting values typically remaining consistent within the uncertainties. As such, these variations are most likely contained within the uncertainties of the PSD fitting. These values are reported in Table 4 . Table 4. The best-fitting parameters of the two models (power-law and bending-power-law) fitted to the PSDs of NGC 3227 in three energy bands: 0.3–10, 0.3–1, and 1–10 keV. The fits are applied to all six XMM–Newton EPIC-pn observations from 2016. See Section 3.5 for details. We then searched for evidence of a break (or bend) in the PSD by fitting a bending power law (plus a constant): where N is the normalization, ν b is the break frequency, and and are the spectral indices below and above the bend, respectively (see González-Martín Vaughan 2012 for further details, who find that a significant bend is detected in the PSDs of 15 out of their sample of 104 AGN observed with XMM–Newton ). Fitting equation ( 3 ) to the 0.3–10 keV PSD improves the fit by Δ S = 10 for two additional free parameters, suggesting the marginal detection of a bend. The low-frequency slope, , is consistent with a value of 1, consistent with the X-ray PSD slopes observed in other Seyfert galaxies. Meanwhile, the high-frequency slope above the bend is steeper, with , where the best-fitting bend frequency is Hz, largely consistent with previous results (Uttley McHardy 2005 ; González-Martín Vaughan 2012 ; Arévalo Markowitz 2014 ). Extending this fit to the soft and hard bands, we find consistent results (Δ S = 9 and Δ S = 10, respectively) with break frequencies of and Hz and high-frequency slopes of and , respectively. Again, the bend detection is marginal and we find no evidence of any energy-dependence of the PSD. The best-fitting values are summarized in Table 4 and the bending-power-law fit is shown in Fig. 9 . In Fourier-based PSD analysis, it is
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