Simultaneous fits of the data by synthetic light curves. Upper panel: Best fit to the data, shown as blue lines, using a Triton surface pressure of p_surf = 14.54 μbar and other parameters provided in Table 1. The residuals (observations minus model) are shown in green. The lower and upper dotted horizontal lines mark the zero flux and the average flux of Triton plus the star, respectively. Each light curve is normalized to the total flux of Triton plus the star and is plotted over a time interval of 6 minutes. The red tick marks indicate 14:41:40 UT. The HCT light curve was binned over five data points (1.05-second time resolution) for a better comparison with the other light curves. We note that a faint central flash is present in the Yanqi Lake light curve. The 1σ error bars are obtained with the PRAIA software, which accounts for the instrumental and photon noises, knowing that the error bars for the CHEOPS data points are dominated by photon noise (see Appendix A). They are not visible here because they are smaller than the plotted dots. Lower panel: χ² map of the simultaneous fits. The 1σ and 3σ level curves are shown in green.