Qualification of the X-ray spectral performance of the DEPFET pixels of the DSSC imager

The first DEPFET module (128 x 512 pixels) of the DSSC pixel detector, designed for user experiments at the European XFEL, has been fully instrumented and an experimental campaign has been carried out with X-ray lines to qualify the main performance figures and to collect calibration data. X-ray spectra fitting has been optimized with consideration to the main sources of systematic errors to achieve gain calibration within 1% accuracy, which is a key issue for its successful operation at the European XFEL. The most important result is the equivalent noise charge of 16 el rms on average. This shows the potential of the DEPFET-based pixel to reach single-photon imaging down to the lowest photon energy (0.25 keV) at 4.5 MHz frame frequency that can be extrapolated at camera level with high confidence.