absolute QE of the systems. This was done by using a NIST calibrated diode in the beam, and the results are shown in Figure 13. This way we can convert from source counts to incident photons. To plan observations through the entire telecope we need to include an extra factor for the telescope optics and filter throughputs as well. These will be published and updated on the proposal website for the mission, once established.

The absolute QE of the FUV detector at the wavelength of observation (150nm) is measured at close to 3%. This gives a conversion from the source total signal in the plots to photons at the photocathode of 0.77. That is, we multiply the source counts by 0.77 to get the incident photon counts. The NUV wavelength used was 210nm, at which the QE is close to 10%, and the QE for the visible is also close to 10%. This gives a conversion factor from plotted source signal to photons of 0.37 for these channels.

Detection of double-photon events
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As noted in paper 1, double-photon events can be flagged by using the max-min corner pixel values from the 5 x 5 events boxes. It is these 