KEYWORDS: Space operations, Data processing, Photovoltaics, Equipment, Calibration, Source mask optimization, Information technology, Data archive systems, Satellites, X-rays
The X-Ray Imaging and Spectroscopy Mission (XRISM) is an international X-ray observatory developed by Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA) in collaboration with European Space Agency (ESA), successfully launched in September 2023. Since the early stage of the project, the XRISM science operations team (SOT) was organized independently of the spacecraft bus system and mission instrument development teams, having prepared for the in-orbit science operations to maximize the scientific outputs. During about half year for the initial operation phase after launch, operations for the mission instruments were started, and the quick-look and the pipeline processes were carried out by SOT in order to check the functions of the instruments. After transition to the nominal operation phase, we started the target observations in the performance verification phase, whose short and long-term observation plans are considered by SOT, including planning the target of opportunity observations. The information on the observation modes of the mission instruments and the status of the data processing is maintained collectively in database synchronized between JAXA and NASA. We also performed the performance verification and optimization activities which provide the well-calibrated data, appropriate tools, and analysis methods for the users and established a help desk that supports the XRISM data analysis. The publicly solicited observation for the guest observer will be started from August or September 2024. These daily science operations are being carried out by dedicated scientists belonging to JAXA in collaboration with the other SOT members, the mission operations team and the instrument teams. This paper will introduce the ground system for the XRISM science operations and report on the activities of the SOT from the launch to today and plans for future science operations.
Semiconductor Compton telescope (SCT) is one of the promising technologies in cosmic MeV gamma-ray observation, because of good angular resolution measure thanks to its high energy and positional resolutions. However, it cannot be better than a few degrees because of quantum limitation, known as doppler broadening. With improving sensitivity in MeV astronomy, realization of 10-arcmin-level of angular resolution is becoming more important. Combining a coded-aperture mask imaging to SCT is the simplest measure to obtain this level of angular resolution in MeV astronomy. Since the mask made of heavy metal is a BGD source and contribution from bright sources and CXB limits the statistical significance of the mask decoding, we propose the concept of attaching a coded mask to a narrow-field Si/CdTe SCT such as the SGD on the ASTRO-H mission. We developed a concept verification system, mini-SGI, adopting 0.5 mm thick DSSDs and 2 mm thick CdTe-DSD, covered with BGO active shield. By irradiating a 133Ba source, we succeeded to obtain 1° resolution coded-mask imaging applied to Compton reconstructed image with ARM resolution of 9.8 degree and 3.0 degree to 81 keV and 356 keV lines, respectively.
The MeV band covers the physics of the lowest energy end of the non-thermal universe and nuclear reactions in metal synthesis and/or matters interacting with cosmic rays. Nevertheless, sensitivity in this band is still limited. Improving MeV sensitivity is one of the most important issues in modern astronomy. The soft gamma-ray detector (SGD) onboard the Hitomi satellite launched in 2016 was an innovative narrow field-of-view semiconductor Compton telescope (SCT), which aims at background reduction through deep active-shielding combined with SCT using Si and CdTe, a Si/CdTe-SCT. Although with a limited operation time, it is the sole SCT proven in orbit to date, and succeeded in detecting ∼ 100 keV polarization with only 5 ks exposure. Based on these achievements, we propose a new approach “narrow field-of-view Si/CdTe-SCT at balloon altitude”. At the altitude of 32-40 km, detectors do not suffer severe proton bomberment, which was one of the major contributor to the SGD background, while able to observe MeV gamma rays from the universe. Atmospheric gamma rays is non-negligible, but as it is stronger near horizon, narrowing the field-of-view and aiming around zenith will cut most of them. The detector loses wide field of view, but can be used as a probe in sub-MeV band. As the first step of this approach, we are planning a balloon experiment, miniSGD, to confirm the concept. It is very compact and not aiming at real observation, but has all the components integrated within the 40 × 40 × 50 cm3 volume, including detectors, electronics and the collimator. The Si/CdTe-SCT was made of a single layer of 0.5 mm thick double-sided Si strip detectors (DSSDs) and newly developed 2 mm thick CdTe double sided strip detectors (CdTe-DSDs), surrounded by nine units of 2-3 cm thick BGO scintillator crystals. The miniSGD experiment is to fly as a piggy-back payload in the 2023 Spring campaign of JAXA Ballooning team at Alice Springs, Australia. Technologies to be verified in miniSGD are also applicable to the future hard X-ray missions, such as the FORCE mission.
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