Energy gain scale calibration of the XRISM Resolve microcalorimeter spectrometer: ground calibration results and on orbit comparison

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 presentation we describe our ground calibration strategy and results of calibration campaigns from 2018-2022, including a discussion of improvements in the ground calibration approach compared to Hitomi and a description of Resolve's final pre-launch gain scales, which indicate that the energy scale of the array can be absolutely calibrated to better than +/- 0.5 eV from 0.3-17.5 keV. We provide an assessment of how well these pre-launch gain scales correct on-orbit data and discuss approaches for updating the gain curves.