Estimator distribution for simulated constant light curves. Top panel: amplitude maximum deviation significance (Eq. (9)). Bottom panel: significance of the excess variance and variability fraction (Eq. (16)). Each coloured histogram represents a set of simulations with the indicated constant input count rate. For the full data set (black histogram), black downward triangles point to the 2, 3, and 4σ equivalent quantiles of the distribution.