Number of light curves with at least one negative bin by more than Nσ and the overall number of bins below this threshold. The horizontal green line indicates the overall number of bins (8 × 10⁷) in 500 s bin light curves, and the green dots show their number at least Nσ below 0. Similarly, we show the light curves that contain these points in brown. The vertical separation between green and brown dots indicates the average number of negative bins per light curve. The number of bins per light curve increases as the threshold decreases.