Top panel: dLW time series for GL 480, and the fitted GP model overlaid in red. Middle panel: Residuals after subtracting the GP model from the observations. Bottom panel: Bayesian periodograms for the activity signal (black curve) and residuals (red curve), plotted as a function of period (in days). The dashed green lines in the bottom panel mark periodicities at the stellar rotation period (P_rot), at the one-half rotation period (P_rot/2), and at the one-third rotation period (P_rot/3). The significance level of log BF = 5 is indicated by the horizontal red dashed line.