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The Resolve instrument aboard the X-ray Imaging and Spectroscopy Mission (XRISM) is a 36-pixel microcalorimeter spectrometer that provides non-dispersive spectroscopy with 5 eV spectral resolution in the soft x-ray waveband. Resolve has a requirement to provide absolute energy-scale calibration of ± 2 eV from 0.3–12 keV. In this manuscript we describe our ground calibration strategy and results of a subset of the ground calibration campaigns, including a discussion of improvements in the energy scale ground calibration compared to Hitomi's. These improvements include calibration of the low-energy band below 4 keV with the instrument in the flight dewar and the dewar aperture door open, which was not performed for Hitomi, and thorough measurements over an extended high-energy waveband to 22 keV. We also developed an improved technique for gain calibration of 'mid-res' secondary events, which have suppressed gain due to proximity to a preceding x-ray event (18-70 ms) on the same pixel. We provide an assessment of how well these pre-launch gain scales correct on-orbit data and discuss approaches for updating the gain curves. Energy-scale calibration approaches for future space-based instruments, including the X-ray Integral Field Unit (X-IFU) on Athena and the microcalorimeter spectrometer proposed for the Line Emission Mapper (LEM), have heritage in the calibration of XRISM. We briefly comment on lessons learned from Resolve calibration that are relevant for these future instruments.
Eckart et al. (Wed,) studied this question.