Left: Illustrative examples of DRW time series with different damping timescales and variation amplitudes. Here SF_inf is the structure function of the process at infinitely large separations in time and is related to the root mean square brightness fluctuation amplitude, σ_CAR, by SF${}_{inf}=\sqrt{2}{\sigma }_{\mathrm{CAR}}$. Right: Expected power spectrum for the DRW superimposed on the periodogram obtained from the green time series of the left image. Note that in both panels, the y axis is reported in arbitrary units.