We will use the \citet{Zoghbi_2013} method to construct the PSDs from both the Swift/BAT and NuSTAR light curves. An added advantage of NuSTAR is that two light curves from each observation, one from each detector. This will allow us to average the two PSDs from each detector together to get an even better estimate at higher frequencies where the variability is expected to be much lower compared to longer timescales.

One source of uncertainty currently is the choice of frequency bins to use when constructing the PSD. \citet{Zoghbi_2013} cites using bins that contain at least 10 Fourier frequencies, however we will need to investigate the optimum choice.