Ground calibrations of the Solar Intensity X-ray Spectrometer (SIXS) on board BepiColombo

Abstract In this paper we present the methods, results, and analysis of the BepiColombo SIXS instruments' ground calibrations. The aim of these calibrations was to characterize the performance of the three SIXS X-ray detectors to enable reliable spectral analysis of the solar X-ray data. The ground calibrations for characterizing the performance of the three separate HPSi (High-Purity Silicon) PIN (Positive Intrinsic Negative) X-ray detectors included the following tasks. Determination of the energy resolution as a function of photon energy at different operational temperatures, determination of the detector sensitivity within the FoV (Field of View) as a function of the off-axis and roll angles, pile-up tests for determining the speed of the read out electronics, measurements of the low energy threshold of the energy scale, i.e. the minimum measurable photon energy corresponding to the adjustable software parameter, a comparison calibration of the fluorescence line fluxes with the SMART-1 XSM FS (Flight Spare) detector, and determination of the shifting of the energy scale as a function of the ambient temperature. We also describe the method and results of determining the geometrical area of the detector apertures based on the image analysis of very high resolution photographs obtained with by the Scanning Electron Microscope (SEM).