Detail design of the XRISM timing system and its verification in the nominal operation mode

The XRISM is the newly born X-ray satellite led by JAXA and NASA in collaboration with ESA, aiming to perform high-resolution spectroscopy of many astronomical X-ray objects. In the era of multi-messenger astronomy, where observations are performed in various wavelengths and include neutrino and gravitational data, it is important for the observatories to assign precise time of photons. To achieve the science goals of the XRISM mission, an absolute timing accuracy of 1.0 ms is required for the Resolve. The timing system, including both onboard instruments and off-line data-processing tools, is designed to meet this requirement. Following the lessons of the previous X-ray mission of Hitomi, comprehensive list of items that affect the accuracy of the timing are listed together with the timing error budget. During the system design and verification phases on the ground, all elements are controlled and verified to be within the budgets at the component level. After the launch of the satellite on 7 September 2023, in the initial commissioning phase, the overall timing performance of the timing system is scheduled to be confirmed to satisfy the timing requirements using a millisecond pulsar. The XRISM spacecraft carries the GPS receiver and the timing system uses the GPS signals in the nominal operation mode. In this presentation, we summarize the detailed design of the timing system of the XRISM, and the results of the timing verification tests both on ground and in orbit in the nominal operation mode. Detailed results on the failure mode of the GPS receiver will be presented in another presentation.