This paper describes the strategy and planned implementation of the ground calibration of the X-IFU microcalorimeter spectrometer on-board Athena, the X-ray observatory from ESA to be launched after the mid-2030s. X-IFU is the second generation of space microcalorimeter instrument, and its calibration strategy benefits from the experience acquired on the present Japanese-US built Resolve instrument on-board XRISM. This calibration plan takes into account the reformulation of the Athena mission and its instruments that took place in 2022-23. The X-IFU calibration strategy is presented along with the set of X-ray sources needed for the ground calibration and the the definition of the sequences for using them.
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.
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 X-ray Imaging and Spectroscopy Mission (XRISM) is an X-ray astronomy satellite successfully launched in September 2023. The satellite carries two X-ray telescopes with a focal length of 5.6 meters. One of these is Resolve, which consists of an X-ray Mirror Assembly (XMA) and a microcalorimeter array, providing a relatively narrow field of view (FoV) of 3.05 arcminutes squared. The other is Xtend, which consists of an XMA and an X-ray CCD camera, offering a large FoV of 38 arcminutes squared. Due to Resolve’s limited FoV, pointing accuracy is crucial for stable observation. The observation aimpoint, defined as the position on the focal plane where an on-axis target is located, was verified within a few arcseconds of the center of the array after the satellite’s boresight correction. It was also confirmed to be suitable, with no significant irreversible shift detected over approximately half a year. In the commissioning phase, all measurable requirements for pointing accuracy were confirmed to be met. The absolute pointing determination accuracies are less than 20 arcseconds for both instruments. The aimpoint shift and its temperature dependence were also assessed for each detector. The aimpoint shifts of both instruments in each observation have a good correlation on the X-axis, but not on the Y-axis in the detector coordinates. Resolve’s Y-axis shift clearly depends on the base panel temperature, on the order of a few arcseconds, which can be ignored for the absolute control accuracy and effective area. The sharp PSF core with an FWHM of approximately 10 arcseconds and arcsecond-scale relative determination accuracy enable Xtend to achieve good image reconstruction performance.
The X-Ray Imaging and Spectroscopy Mission (XRISM) project at JAXA officially started in 2018. Following the development of onboard components, the proto-flight test was conducted from 2021 to 2023 at JAXA Tsukuba Space Center. The spacecraft was launched from JAXA Tanegashima Space Center on September 7, 2023 (JST), and onboard components, including the science instruments, were activated during the in-orbit commissioning phase. Following the previous report in 2020, we report the spacecraft ground tests, the launch operation, in-orbit operations, and the status and plan of initial and subsequent guest observations.
The XRISM (X-Ray Imaging and Spectroscopy Mission) satellite was successfully launched and put into low- Earth orbit on September 6, 2023 (UT). The Resolve instrument onboard XRISM hosts an x-ray microcalorimeter detector, which was designed to achieve a high-resolution (≤7 eV FWHM at 6 keV), high-throughput, and nondispersive spectroscopy over a wide energy range. It also excels in a low background with a requirement of < 2 × 10−3 s−1 keV−1 (0.3–12.0 keV), which is equivalent to only one background event per spectral bin per 100 ks exposure. Event screening to discriminate x-ray events from background is a key to meeting the requirement. We present the result of the Resolve event screening using the data sets on the ground and in the orbit based on the heritage of the preceding x-ray microcalorimeter missions, in particular, the Soft X-ray Spectrometer (SXS) onboard ASTRO-H. We optimize and evaluate 19 screening items of three types based on (1) the event pulse shape, (2) relative arrival times among multiple events, and (3) good time intervals. We show that the initial screening, which is applied for science data products in the performance verification phase, reduces the background rate to 1.8×10−3 s−1 keV−1 meeting the requirement. We further evaluate the additional screening utilizing the correlation among some pulse shape properties of x-ray events and show that it further reduces the background rate particularly in the <2 keV band. Over 0.3–12 keV, the background rate becomes 1.0 × 10−3 s−1 keV−1.
The Resolve instrument aboard the X-ray Imaging and Spectroscopy Mission (XRISM) is a 36-pixel microcalorimeter spectrometer that provides non-dispersive spectroscopy with 5 eV spectral resolution in the soft x-ray waveband. Resolve has a requirement to provide absolute energy-scale calibration of ± 2 eV from 0.3–12 keV. In this manuscript we describe our ground calibration strategy and results of a subset of the ground calibration campaigns, including a discussion of improvements in the energy scale ground calibration compared to Hitomi’s. These improvements include calibration of the low-energy band below 4 keV with the instrument in the flight dewar and the dewar aperture door open, which was not performed for Hitomi, and thorough measurements over an extended high-energy waveband to 22 keV. We also developed an improved technique for gain calibration of ‘mid-res’ secondary events, which have suppressed gain due to proximity to a preceding x-ray event (18-70 ms) on the same pixel. We provide an assessment of how well these pre-launch gain scales correct on-orbit data and discuss approaches for updating the gain curves. Energy-scale calibration approaches for future space-based instruments, including the X-ray Integral Field Unit (X-IFU) on Athena and the microcalorimeter spectrometer proposed for the Line Emission Mapper (LEM), have heritage in the calibration of XRISM. We briefly comment on lessons learned from Resolve calibration that are relevant for these future instruments.
The Resolve instrument was launched on-board the XRISM observatory in early September 2023. The Resolve spectrometer is based on a high-sensitivity X-ray calorimeter detector system that has been successfully deployed in many ground and sub-orbital spectrometers. However, the Resolve instrument will be the first long-term implementation in space. The instrument will provide essential diagnostics for nearly every class of X-ray emitting objects, from the atmosphere of Jupiter to the outskirts of galaxy clusters, without degradation for spatially extended objects. The Resolve detector system consists of a 36-pixel microcalorimeter array operated at a heat-sink temperature of 50mK. In pre-flight testing, the detector system demonstrated a resolving power of better than 1300 at 6 keV with a simultaneous bandpass from below 0.3 keV to above 12 keV and a timing precision better than 100 μs. An anti-coincidence detector placed directly behind the microcalorimeter array effectively suppresses background. The detector energy-resolution budget included terms for interference from the Resolve cooling system and the spacecraft. Additional terms for energy-scale stability, on-orbit effects, and use of mid-grade events were also included, predicting an end-of-life, on-orbit performance for high and mid-grade events that meets the requirement of 7 eV FWHM at 6 keV. Here we discuss the actual on-orbit performance of the Resolve detector system and compare this to performance in pre-flight testing, on-orbit predictions, and the almost identical Hitomi/SXS instrument. We will also discuss the on-orbit gain stability, any additional on-orbit interference, and measurements of the on-orbit background.
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.
The resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM) consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput x-ray mirror assembly (XMA) with a focal length of 5.6 m. XRISM is a recovery mission of ASTRO-H/Hitomi, and the Resolve instrument is a rebuild of the ASTRO-H soft x-ray spectrometer (SXS) and the Soft X-ray Telescope (SXT) that achieved energy resolution of ∼5 eV FWHM on orbit, with several important changes based on lessons learned from ASTRO-H. The flight models of the Dewar and the electronics boxes were fabricated and the instrument test and calibration were conducted in 2021. By tuning the cryocooler frequencies, energy resolution better than 4.9 eV FWHM at 6 keV was demonstrated for all 36 pixels and high resolution grade events, as well as energy-scale accuracy better than 2 eV up to 30 keV. The immunity of the detectors to microvibration, electrical conduction, and radiation was evaluated. The instrument was delivered to the spacecraft system in 2022-04 and is under the spacecraft system testing as of writing. The XMA was tested and calibrated separately. Its angular resolution is 1.27′ and the effective area of the mirror itself is 570 cm2 at 1 keV and 424 cm2 at 6 keV. We report the design and the major changes from the ASTRO-H SXS, the integration, and the results of the instrument test.
The super DIOS mission is a candidate of Japanese future satellite program after 2030’s and this scientific concept has been approved to establish an ISAS/JAXA research group. The main aim of the super DIOS is a x-ray survey to quantify of baryons, over several scales, from the circumgalactic medium around galaxies, cluster outskirts to the warm-hot intergalactic medium along the large cosmic structure by detections of the redshifted emission lines from OVII, OVIII and other ions, for investigating the dynamical state of baryons, including energy flow and metal cycles, in the universe. The super DIOS will have a resolution of 15 arcseconds and 3 kilo-pixels of transition edge sensor (TES) and its micro-wave SQUID multiplexer read-out system. This performance resolves most contaminating x-ray sources and reduces the level of diffuse x-ray background after subtracting point-like sources. The technical achievements of on-board cooling system reached by the Hitomi (ASTRO-H) and XRISM for microcalorimeter provide baseline technology for Super DIOS. We will also have a large scale collaborations with multi wave-length survey projects such as optical and radio survey observations.
We report the development of an optical encoder and its readout system for a cryogenically-cooled continuously rotating half-wave plate (HWP) polarization modulator unit (PMU) in the LiteBIRD low-frequency telescope. LiteBIRD is a cosmic microwave background polarization satellite mission to probe B-mode polarization, which originates from primordial gravitational waves, observing from the second Lagrange point (L2). LiteBIRD employs a continuously-rotating HWP to mitigate systematic effects. The knowledge of the position angle of the HWP is in a one-to-one relationship to the incident polarization angle. The required reconstruction accuracy is about 1 arcmin and the targeted rotational frequency stability is 1 mHz. A unique development constraint comes from a telemetry bandwidth limitation between the Earth and L2, and thus we implement a digital process to reduce the data volume assuming a future implementation of on-board processing of the encoder data before the downlink. The demonstrations were done experimentally using a breadboard model of the PMU: a readout system using FPGA (Spartan-6) and a rotational mechanism using a superconducting magnetic bearing and AC motor. We acquired the encoder data from the rotational mechanism operating under two conditions: liquid nitrogen at room pressure and below 10 K in a cryostat. We demonstrated the reconstruction of the position angle accuracy < 0.5 arcmin and the corresponding data volume of 0.12 GB/day, which is at least an order of magnitude smaller than the total data volume per day. We further discuss the sources of the position angle uncertainty and its implications to the observations.
The X-Ray Imaging and Spectroscopy Mission (XRISM) is the successor to the 2016 Hitomi mission that ended prematurely. Like Hitomi, the primary science goals are to examine astrophysical problems with precise highresolution X-ray spectroscopy. XRISM promises to discover new horizons in X-ray astronomy. XRISM carries a 6 x 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly and a co-aligned X-ray CCD camera that covers the same energy band over a large field of view. XRISM utilizes Hitomi heritage, but all designs were reviewed. The attitude and orbit control system were improved in hardware and software. The number of star sensors were increased from two to three to improve coverage and robustness in onboard attitude determination and to obtain a wider field of view sun sensor. The fault detection, isolation, and reconfiguration (FDIR) system was carefully examined and reconfigured. Together with a planned increase of ground support stations, the survivability of the spacecraft is significantly improved.
We are studying an improved DIOS (Diffuse Intergalactic Oxygen Surveyor) program, Super DIOS, which is accepted for establishing the Research Group in ISAS/JAXA, for a launch year after 2030. The aim of Super DIOS is an X-ray quantitative exploration of ”dark baryon” over several scales from circumgalactic medium, cluster outskirt to warm-hot intergalactic medium along the Cosmic web with mapping redshifted emission lines from mainly oxygen and other ions. These observations play key roles for investigating the physical condition, such as the energy flow and metal circulation, of most baryons in the Universe. This mission will perform wide field X-ray spectroscopy with a field of view of about 0.5–1 degree and energy resolution of a few eV with TES microcalorimeter, but with much improved angular resolution of about 10–15 arcseconds. We will also consider including a small gamma-ray burst monitor and a fast repointing system. We will have an international collaboration with US and Europe for all the onboard instruments.
The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5’ equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on ∼ 5” pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at ∼ 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 μm. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of ∼ 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (< 50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018.
The Resolve instrument onboard the X-ray Astronomy Recovery Mission (XARM) consists of
an array of 6x6 silicon-thermistor microcalorimeters cooled down to 50 mK
and a high-throughput X-ray mirror assembly with a focal length of 5.6 m.
The XARM is a recovery mission of ASTRO-H/Hitomi,
and is developed by international collaboration of Japan, USA, and Europe.
The Soft X-ray Spectrometer (SXS) onboard Hitomi demonstrated high resolution
X-ray spectroscopy of ~ 5 eV FWHM in orbit for most of the microcalorimeter pixels.
The Resolve instrument is planned to mostly be a copy of the Hitomi SXS and
Soft X-ray Telescope designs, though several changes are planned
based on the lessons learned of Hitomi.
The energy resolution budget of the microcalorimeters is updated,
reflecting the Hitomi SXS results.
We report the current status of the Resolve instrument.
The ASTRO-H mission was designed and developed through an international collaboration of JAXA, NASA, ESA, and the CSA. It was successfully launched on February 17, 2016, and then named Hitomi. During the in-orbit verification phase, the on-board observational instruments functioned as expected. The intricate coolant and refrigeration systems for soft X-ray spectrometer (SXS, a quantum micro-calorimeter) and soft X-ray imager (SXI, an X-ray CCD) also functioned as expected. However, on March 26, 2016, operations were prematurely terminated by a series of abnormal events and mishaps triggered by the attitude control system. These errors led to a fatal event: the loss of the solar panels on the Hitomi mission. The X-ray Astronomy Recovery Mission (or, XARM) is proposed to regain the key scientific advances anticipated by the international collaboration behind Hitomi. XARM will recover this science in the shortest time possible by focusing on one of the main science goals of Hitomi,“Resolving astrophysical problems by precise high-resolution X-ray spectroscopy”.1 This decision was reached after evaluating the performance of the instruments aboard Hitomi and the mission’s initial scientific results, and considering the landscape of planned international X-ray astrophysics missions in 2020’s and 2030’s. Hitomi opened the door to high-resolution spectroscopy in the X-ray universe. It revealed a number of discrepancies between new observational results and prior theoretical predictions. Yet, the resolution pioneered by Hitomi is also the key to answering these and other fundamental questions. The high spectral resolution realized by XARM will not offer mere refinements; rather, it will enable qualitative leaps in astrophysics and plasma physics. XARM has therefore been given a broad scientific charge: “Revealing material circulation and energy transfer in cosmic plasmas and elucidating evolution of cosmic structures and objects”. To fulfill this charge, four categories of science objectives that were defined for Hitomi will also be pursued by XARM; these include (1) Structure formation of the Universe and evolution of clusters of galaxies; (2) Circulation history of baryonic matters in the Universe; (3) Transport and circulation of energy in the Universe; (4) New science with unprecedented high resolution X-ray spectroscopy. In order to achieve these scientific objectives, XARM will carry a 6 × 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces the science objectives, mission concept, and observing plan of XARM.
We are working on an updated program of the future Japanese X-ray satellite mission DIOS (Diffuse Intergalactic Oxygen Surveyor), called Super DIOS. We keep the main aim of searching for dark baryons in the form of warmhot intergalactic medium (WHIM) with high-resolution X-ray spectroscopy. The mission will detect redshifted emission lines from OVII, OVIII and other ions, leading to an overall understanding of the physical nature and spatial distribution of dark baryons as a function of cosmological timescale. We are working on the conceptual design of the satellite and onboard instruments, with a provisional launch time in the early 2030s. The major changes will be improved angular resolution of the X-ray telescope and increased number of TES calorimeter pixels. Super DIOS will have a 10-arcsecond resolution and a few tens of thousand TES pixels. Most contaminating X-ray sources will be resolved, and the level of diffuse X-ray background will be reduced after subtraction of point sources. This will give us very high sensitivity to map out the WHIM in emission. The status of the spacecraft study will be presented: the development plan of TES calorimeters, on-board cooling system, X- ray telescope, and the satellite system. The previous study results for DIOS and technical achievements reached by the Hitomi (ASTRO-H) mission provide baseline technology for Super DIOS. We will also consider large scale international collaboration for all the on-board instruments.
The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.
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