Results of Accelerometer Monitor in the Ground Testing of Resolve X-Ray Microcalorimeter Instrument Onboard XRISM

The Resolve instrument onboard the XRISM satellite is equipped with 6 × 6 x-ray microcalorimeter detectors aiming at an energy resolution of 7 eV (FWHM) at 5.9 keV. It is currently under development by an international collaboration and will be launched in 2023. The detectors are operated at 50 mK, which is achieved by a combination of four Stirling coolers (STC), one Joule-Thomson cooler (JTC), three-stage adiabatic demagnetization refrigerators, and superfluid helium inside the dewar. The cryocoolers (STC and JTC) are significant sources of microphonic noise against the detector performance. To understand and characterize the microphonic propagation, we monitored the level of vibration throughout the ground instrument-level tests in 2019–2022, yielding a rich and unique data set of the accelerometers and the detector at 50 mK amounting to 1720 hours (6.2 Ms). In this article, we report the result of classifying thermal and non-thermal microcalorimeter noise, distinguishing the origin of the noise, and the method for optimizing the cooler drive frequency that minimizes the effect of the noise originating from the cooler.