X-Ray Imaging and Spectroscopy Mission (X線分光撮像衛星)

Diagram of the XRISM observatory
Names	XRISM ASTRO-H Successor ASTRO-H2 XARM
Mission type	X-ray astronomy
Operator	JAXA
COSPAR ID	2023-137A
SATCATno.	57800
Website	xrism.isas.jaxa.jp/en www.nasa.gov/content/goddard/xrism-x-ray-imaging-and-spectroscopy-mission
Mission duration	3 years (planned) 2 years, 159 days (elapsed)
Spacecraft properties
Spacecraft type	ASTRO
Bus	ASTRO-H
Launch mass	2,300 kg (5,100 lb)
Start of mission
Launch date	6 September 2023, 23:42:11 UTC[1]
Rocket	H-IIA 202
Launch site	Tanegashima,LA-Y1
Contractor	Mitsubishi Heavy Industries
Orbital parameters
Reference system	Geocentric orbit
Regime	Low Earth orbit
Perigee altitude	550 km
Apogee altitude	550 km
Inclination	31.0°
Period	96.0 minutes
Main telescope
Name	Soft X-ray Telescope
Diameter	45 cm (18 in)[2]
Focal length	5.6 m (18 ft)
Instruments Resolve Soft X-ray Spectrometer Xtend Soft X-ray Imager
ASTRO program ← Hitomi (ASTRO-H)

TheX-Ray Imaging and Spectroscopy Mission (XRISM, pronounced 'crism'^[3] or 'krizz-em',^[4] as if the X was achi), is anX-rayspace telescope. It is a mission of theJapan Aerospace Exploration Agency (JAXA) in partnership withNASA andESA, intended to studygalaxy clusters, outflows fromgalaxy nuclei, anddark matter.^[5][6]

XRISM is a next generationX-ray astronomy spacecraft, succeeding theChandra X-ray Observatory andXMM-Newton.^[2][7] XRISM is intended to fill a gap in observational capabilities between the anticipated retirement of those older X-ray telescopes and the future launch of the plannedAdvanced Telescope for High Energy Astrophysics (ATHENA). TheHitomi X-ray telescope was intended to fill that gap, but destroyed itself a few weeks after launch in 2016.^[2][7] XRISM replaces Hitomi's role of filling the expected observational gap.

During its early design phase, XRISM was known as the "ASTRO-H Successor" or "ASTRO-H2". After the loss of Hitomi, the nameX-ray Astronomy Recovery Mission (XARM) was used, the R in the acronym referring to recovering Hitomi's capabilities. The name was changed to XRISM in 2018 when JAXA formally initiated the project team.^[8]

With the retirement ofSuzaku in September 2015, and the detectors onboardChandra X-ray Observatory andXMM-Newton operating for more than 15 years and gradually aging, the failure ofHitomi meant that X-ray astronomers would have a 13-year blank period in soft X-ray observation, until the launch of ATHENA in 2035.^[a][2][7][9] This would result in a major setback for the international community,^[10] as studies performed by large scale observatories in other wavelengths, such as the James Webb Space Telescope and theThirty Meter Telescope were planned to commence in the early 2020s, while there would be no telescope to cover the most important part of X-ray astronomy.^[2][7] A lack of new missions could also deprive young astronomers a chance to gain hands-on experience from participating in a project.^[2][7] Along with these reasons, motivation to recover science that was expected as results fromHitomi, became the rationale to initiate theXRISM project.XRISM has been recommended by ISAS's Advisory Council for Research and Management, the High Energy AstroPhysics Association in Japan, NASA Astrophysics Subcommittee, NASA Science Committee, NASA Advisory Council.^[7][11]

With its successful launch in September 2023,^[1]XRISM is expected to cover the science that was lost withHitomi, such as the structure formation of the universe, feedback from galaxies/active galaxy nuclei, and the history of material circulation from stars to galaxy clusters.^[6] The space telescope will also take overHitomi's role as a technology demonstrator for the EuropeanAdvanced Telescope for High Energy Astrophysics (ATHENA) telescope.^[9][12][13] Multiple space agencies, includingNASA and theEuropean Space Agency (ESA) are participating in the mission.^[14] In Japan, the project is led by JAXA'sInstitute of Space and Astronautical Science (ISAS) division, and U.S. participation is led by NASA'sGoddard Space Flight Center (GSFC). The U.S. contribution is expected to cost around US$80 million, which is about the same amount as the contribution toHitomi.^[15][16]

The X-ray Imaging and Spectroscopy Mission is one of the first projects for ISAS to have a separate project manager (PM) and primary investigator (PI). This is part of ISAS's reform in project management to prevent the recurrence of theHitomi accident.^[7] In traditional ISAS missions, the PM was also responsible for tasks that would typically be allocated to PIs in a NASA mission.

WhileHitomi had an array of instruments spanning from soft X-ray to soft gamma ray,XRISM focuses around the Resolve instrument (equivalent toHitomi's soft X-ray spectrometer),^[17] as well as Xtend (SXI), which has a high affinity to Resolve.^[18] The elimination of a hard X-ray telescope was justified by the 2012 launch of NASA'sNuSTAR satellite, which did not exist whenHitomi (then known as the New X-Ray Telescope, NeXT) was initially formulated.^[19][b] NuSTAR's spatial and energy resolution is analogous toHitomi's hard X-ray instruments.^[19] OnceXRISM's operation starts, collaborative observations with NuSTAR will likely be essential.^[6] Meanwhile, the scientific value of the soft and hard X-ray band width boundary has been noted; therefore the option of upgradingXRISM's instruments to be partially capable of hard X-ray observation is under consideration.^{[18][19][needs update]}

A hard X-ray telescope with abilities surpassingHitomi was proposed in 2017.^[20] TheFORCE (Focusing On Relativistic universe and Cosmic Evolution) space telescope is a candidate for the next ISAS competitive medium class mission. If selected,FORCE would be launched after the mid-2020s, with an eye towards conducting simultaneous observations with ATHENA.^[20][6]

Following the premature termination of theHitomi mission, on 14 June 2016 JAXA announced their proposal to rebuild the satellite.^[21] The XARM pre-project preparation team was formed in October 2016.^[22] In the U.S. side, formulation began in the summer of 2017.^[5] In June 2017, ESA announced that they would participate in XARM as a mission of opportunity.^[14]

XRISM carries two instruments for studying the soft X-ray energy range, Resolve and Xtend. The satellite has separate telescopes for each of the instruments, SXT-I (Soft X-ray Telescope for Imager) and SXT-S (Soft X-ray Telescope for Spectrometer).^[7] Both telescopes have a focal length of 5.6 m (18 ft).^[2]

Resolve is an X-raymicro calorimeter developed byNASA and theGoddard Space Flight Center.^[24] The instrument is a duplicate version of itsHitomi predecessor. It used some space-qualified hardware left from the manufacture ofHitomi's SXS.^[25]

Xtend is an X-rayCCD camera. Xtend improves on the energy resolution ofHitomi's SXI.^[26]

JAXA launched XRISM on 6 September 2023 at 23:42 UTC (7 September 08:42 Japan Standard Time) using anH-IIA rocket fromTanegashima Space Center. XRISM was successfully inserted into orbit on the same day, and the accompanying launch payload,SLIM, began its multi-month journey to the Moon.^[1]

A protective shutter over the Resolve instrument's detector has failed to open. This does not prevent the instrument from operating, but limits it to observing X-rays of energy1800 eV and above, as opposed to the planned300 eV.^[27][28] A similar shutter over Xtend has opened normally.

• Suzaku
• List of X-ray space telescopes
• X-ray astronomy

• XRISM official website
• X-Ray Imaging and Spectroscopy Mission (XRISM) at JAXA
• X-ray Imaging and Spectroscopy Mission at NASA Goddard Space Flight Center
• Beyond the loss ofHitomi(in Japanese)

• Space telescopes
• Satellites of Japan
• X-ray telescopes
• Spacecraft launched in 2023
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• Explorers Program
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• 2023 in Japan

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