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The X-Ray Imaging and Spectroscopy Mission (XRISM) is a mission led by Institute of Space and Astronautical Science (ISAS) of Japan Aerospace Exploration Agency (JAXA) in collaboration with the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and other partners in Japan and around the world. Its main purpose is to perform high spectral resolution, high throughput imaging X-ray spectroscopy of celestial X-ray sources. XRISM was lanched on 2023 September 6 (UT) on a JAXA HII-A rocket. As of this writing, the initial in-orbit check-out and commissioning phase of XRISM has just concluded, and 6 months of Performance Verification (PV) observations, whose targets have been chosen by the XRISM Science Team, have started. Subsequently, XRISM will become a general purpose observatory open to all astronomers, with annual calls for proposals issued in parallel by JAXA, NASA, and ESA. In addition, all PV data will enter public archive 1 year after the conclusion of the PV phase; all subsequent observational data will enter public archive after an initial 1-year exclusive use period.
The scientific payload of XRISM consists of two instruments, Resolve and Xtend.
The Resolve instrument has a Gate Valve (X-ray aperture door) that protects the detector on the ground as well as during launch and early operations, and is meant to be opened during commissioning. However, the Gate Valve has not opened, thereby shifting the nominal energy band of Resolve from 0.3–12 keV to 1.7–12 keV and lowering the effective area. While the XRISM team will continue to assess different approaches to opening the Gate Valve, the Cycle 1 program will be carried out with the closed Gate Valve configuration, and therefore this document describes Resolve in this configuration. Note that the Resolve Gate Valve does not affect the Xtend instrument.
5 eV energy resolution in the 1.7–12 keV bandpass with a field of view of 3 arcmin.
38 arcmin
over the energy range 0.4–13 keV. Xtend uses a lightweight XMA identical in design to that used for Resolve.
These instruments are nearly identical to the two soft X-ray instruments flown on Hitomi, a mission that was lost shortly after launch in 20161.1. The Soft X-ray Spectrometer (SXS) on Hitomi and Resolve on XRISM are sufficiently similar, as are the Soft X-ray Imager (SXI) on-board Hitomi and Xtend on XRISM, that the papers based on Hitomi data serve as an excellent guide in preparing XRISM observing proposals. Note also that all Hitomi observations were carried out with the SXS Gate Valve closed. In addition, data formats as well as data analysis and simulation software for XRISM are based largely on those developed for Hitomi.
This document is intended for researchers who have some general understanding of space-based astronomy and X-ray observations. It should provide the readers with a general understanding of the characteristics of Resolve and Xtend, including on-board data handling, calibration, and operational limitations. This document also explains the basics of how XRISM will be operated, and how the observing time will be allocated. Based on this document, the reader should be able to determine whether XRISM is the appropriate instrument to address their scientific question, and how to design appropriate observing program for the proposal.
This document is not intended as a data analysis guide. Neither is it intended to provide in-depth descriptions of the instruments. In addition, the mechanical details of proposal submission will be explained elsewhere.
The document is organized as follows. Chapter 2 summarizes the principal characteristics of the detectors on-board XRISM. Chapter 3 covers how the observing time will be allocated. This includes data rights and time available for General Observers (GOs), as well as policies regarding Targets of Opportunity (TOOs). In addition, observational constraints due to the orbit, Sun angle, and the pointing accuracy are described. The proposal process is reviewed, including how to submit a proposal, how they will be evaluated, and how observations will be scheduled, performed, and the results disseminated.
The subsequent three chapters describe XMA (Chapter 4), Resolve (Chapter 5), and Xtend (Chapter 6). Finally, Chapter 7 and Chapter 8 focus on particular caveats associated with, respectively, extended sources and bright sources, which may thus be of importance for many proposers.
Disclaimer:
The current version of this document was prepared largely based on the best pre-launch understanding of the observatory and its instruments, with some early indications from early commissioning activities. Our understanding of the performance of the mission is expected to evolve, quantitatively if not qualitatively. Any significant new information will be made available at our websites and through other communication channels.