Calibration measurements on the DEPFET Detectors for the MIXS instrument on BepiColombo

The Mercury Imaging X-ray Spectrometer (MIXS) will be launched on board of the 5th ESA cornerstone mission BepiColombo. The two channel instrument MIXS is dedicated to the exploration of the elemental composition of the mercurian surface by imaging x-ray spectroscopy of the elemental fluorescence lines. One of the main scientific goals of MIXS is to provide spatially resolved elemental abundance maps of key rock-forming elements. MIXS will be the successor of the XRS instrument, which is currently orbiting Mercury on board of NASAs satellite MESSENGER. MIXS will provide unprecedented spectral and spatial resolution due to its innovative detector and optics concepts. The MIXS target energy band ranges from 0.5 to 7 keV and allows to directly access the Fe-L line at 0.7 keV, which was not accessible to previous missions. In addition, the high spectroscopic resolution of FWHM ≤ 200 eV at the reference energy of 1 keV after one year in Mercury orbit, allows to separate the x-ray fluorescence emission lines of important elements like Mg (1.25 keV) and Al (1.49 keV) without the need for any filter. The detectors for the energy and spatially resolved detection of x-rays for both channels are identical DEPFET (DEpleted P-channel FET) active pixel detectors. We report on the calibration of the MIXS flight and flight spare detector modules at the PTB (Physikalisch-Technische Bundesanstalt) beamlines at the BESSY II synchrotron radiation facility. Each detector was calibrated at least at 10 discrete energies in the energy range from 0.5 to 10 keV. The excellent spectroscopic performance of all three detector modules was verified.