We present the design and performance of the XRISM Soft X-Ray Spectrometer Resolve, successfully launched on a JAXA H-IIA rocket September 7, 2023. The instrument uses a 36-pixel array of microcalorimeters at the focus of a grazing-incidence x-ray mirror. The instrument has achieved an energy resolution of 4.5 eV (FWHM) at 6. The overall cooling chain was designed to provide a lifetime of at least 3 years in orbit and operate without liquid helium to provide redundancy and the longest operational lifetime for the instrument. Early indications that the cryogen lifetime will exceed 4 years. X-rays are focused onto the array with a high-throughput grazing incidence X-ray Mirror Assembly with over 200 nested two-stage X-ray reflectors. A series of onboard X-ray calibrations sources allow simultaneous energy scale calibration lines simultaneously while observing celestial sources. The inflight performance of Resolve will be described along with a summary of the scientific capabilities.
The initial on-orbit checkout of the soft X-ray spectroscopic system on board the XRISM satellite is summarized. The satellite was launched on September 6, 2023 (UT) and has been undergoing initial checkout since then. Immediately after the launch, the cryocoolers were turned on and their operation was established. The first cycle of the adiabatic demagnetization refrigerator was performed on Oct. 9th, 2023, to transition the sensor to steady-state operational temperature conditions. Subsequently, the filter wheel, which supports energy calibration, was started up. The energy scale is highly sensitive to the temperature environment around the sensor and its analog electronics. The gain correction was established by referring to the calibration X-ray line. For an optimization of the cooler frequencies, we took data including the noise spectra by scanning the cooler frequencies, and selected a good frequency pair in the on-orbit environment. At the last stage of the checkout, the gate valve, which protects the inside of the Dewar from outside air pressure at launch, was attempted to be opened to bring the system to a state where it is ready for regular operations but was failed.
Resolve is the instrument that utilizes an X-ray micro-calorimeter array onboard the XRISM (X-Ray Imaging and Spectroscopy Mission), which was launched on September 6 (UT), 2023. It fully met the spectral performance requirement (7 eV at 6 keV) both on the ground and in orbit and was confirmed to have the same performance as the SXS onboard the ASTRO-H (Hitomi) satellite. The detectors are operated at a low temperature of 50 mK to achieve the required energy resolution with the cooling system to satisfy the lifetime requirement of over 3 years. The cooling system is equipped with a 3-stage ADR and superfluid liquid He (LHe) as the heat sink for the ADR. The Joule-Thomson cooler unit and 2-stage Stirling cooler units are adopted to reduce heat load to the LHe. In the pre-launch operations, we carried out the low-temperature LHe top-off operation. The resultant amount of liquid He was over 35 L at the launch, which is sufficient to meet the lifetime requirement. During the post-launch operation, the LHe vent valve was opened five minutes after launch during the rocket acceleration, and the cryocoolers started in several revolutions as planned which established stable cooling of the dewar.
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