Figure 5: Response of the differential imaging method to the Naked-Eye Burst, as seen by the TORTORA camera software. Left pane: original burst light curve in counts (black line), and corresponding deviations from the mean value over 100 previous points in units of the standard deviation estimated over the same interval (red line). The response is highly non-linear due to the influence of the burst itself on the estimation of the mean and standard deviation. The deviation never exceeds 5 . Right pane: response to a burst with the same temporal structure and brightness, but 30 times shorter than Naked-Eye Burst (2-second duration). There is a sharp 90 peak in deviation.