Two-dimensional histogram showing the joint distribution function of 𝒮 and p at 160′ resolution, using a lag δ = 80′. The black curve is the running mean of 𝒮 as a function of the mean p, in bins of ordered p, with each bin containing the same number of pixels. The error bars represent the standard deviation of 𝒮 in each bin of p. The dashed white line shows our fit 𝒮 = 031/p to this running mean.