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 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.
The in-orbit performance verification and calibration of the X-ray Mirror Assembly (XMA) on the XRISM satellite are ongoing. The optical performance of the XMA is being measured with bright point-like or bright small enough sources in orbit. This paper reports the preliminary results for the XMA of Resolve (Resolve- XMA). The in-orbit on-axis and off-axis (1.8′–9′ away from the aimpoint) Point Spread Function (PSF) of the Resolve-XMA were measured using 3C 273 and Cyg X-2, respectively. No significant changes were found in the PSF compared to on-ground results, indicating that the Resolve-XMA is functioning as expected (HPD ∼ 1.3′). For the Effective Area (EA) calibration, XRISM observed 3C 273 alongside other satellites. The Resolve spectrum of 3C 273 is well reproduced by an absorbed power law. While the best-fit photon index is consistent with that measured by NuSTAR, the flux is 5% higher than the NuSTAR measurement. In-orbit stray light observation was conducted with Crab at 60′ off from the aimpoint, and a signature of stray light on Resolve was detected. The observation of Resolve optical search has not yet been performed, and GX 3+1 has been proposed as the target.
The X-Ray Imaging and Spectroscopy Mission (XRISM) is a collaborative mission between the Japan Aerospace Exploration Agency (JAXA) and the National Aeronautics and Space Administration (NASA), with the participation of the European Space Agency (ESA). This mission is designed to investigate celestial X-ray objects in the Universe with high-throughput imaging and high-resolution spectroscopy, using its Xtend and Resolve instruments. The satellite was successfully launched from Japan in September 2023. The ground-based calibration of the X-ray Mirror Assemblies (XMAs) for both instruments onboard the XRISM satellite was performed at several facilities, almost exclusively at NASA’s Goddard Space Flight Center. A raytracing simulator (xrtraytrace) has been developed by the Hitomi and XRISM teams, and its XRISM model input files have been tuned to reproduce the calibration data. In this paper, we first present the various ground-calibration measurements. We then explain the analyses of the data resulting from these measurements. Next, we show how we used the products of these analyses to tune the simulator parameters in order to match the calibration measurements. Finally, we show a comparison of the simulated results with the measured effective areas, vignetting curves, and point spread functions. We found that the on-axis effective area measurements and the raytracing results are consistent within 6% in the nominal energy band, and the off-axis effective areas at 6.4 keV agree within 5% for Resolve-XMA (up to 5′) and within 8% for Xtend-XMA (up to 20′). Furthermore, the tuned raytracing simulator allows the on-axis PSF to be reproduced with less than 40% accuracy for both XMAs (at 1.5, 6.4 and 9.4 keV).
Xtend is one of the two telescopes onboard the X-ray imaging and spectroscopy mission (XRISM), which was launched on September 7th, 2023. Xtend comprises the Soft X-ray Imager (SXI), an X-ray CCD camera, and the X-ray Mirror Assembly (XMA), a thin-foil-nested conically approximated Wolter-I optics. A large field of view of 38′ × 38′ over the energy range from 0.4 to 13 keV is realized by the combination of the SXI and XMA with a focal length of 5.6 m. The SXI employs four P-channel, back-illuminated type CCDs with a thick depletion layer of 200 μm. The four CCD chips are arranged in a 2×2 grid and cooled down to −110°C with a single-stage Stirling cooler. Before the launch of XRISM, we conducted a month-long spacecraft thermal vacuum test. The performance verification of the SXI was successfully carried out in a course of multiple thermal cycles of the spacecraft. About a month after the launch of XRISM, the SXI was carefully activated and the soundness of its functionality was checked by a step-by-step process. Commissioning observations followed the initial operation. We here present pre- and post-launch results verifying the Xtend performance. All the in-orbit performances are consistent with those measured on ground and satisfy the mission requirement. Extensive calibration studies are ongoing.
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 X-Ray Imaging and Spectroscopy Mission (XRISM) is an x-ray astronomy satellite being developed in collaboration between NASA, JAXA, and ESA, and is scheduled for launch in Japanese fiscal year 2022. The x-ray mirror assembly (XMA) for XRISM has been developed at NASA’s Goddard Space Flight Center (GSFC). Two units were fabricated, one each for a micro-calorimeter array (Resolve) and a CCD array (Xtend). The ground calibration and performance verification measurements for XRISM XMA were taken at the 100-m x-ray beamline at NASA/GSFC. X-ray images at the focal plane were taken by scanning across the entire mirror aperture with a 15 mm×15 mm pencil beam. These measurements were performed at seven different energies including 1.5 keV (Al Kα), 4.5 keV (Ti Kα), 6.4 keV (Fe Kα), 8.0 keV (Cu Kα), 9.4 keV (Pt Lα), 11.1 keV (Pt Lβ), 17.5 keV (Mo Kα). A method for background subtraction was developed using a back-illuminated CCD camera with a 30 mm×30 mm (i.e. 17′×17′) array at the focal plane. Results from the measurements on the imaging performance show a small energy dependence in the angular resolution. We will also present the results of the stray light measurements.
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.
Xtend is a soft x-ray imaging telescope developed for the x-ray imaging and spectroscopy mission (XRISM). XRISM is scheduled to be launched in the Japanese fiscal year 2022. Xtend consists of the soft x-ray imager (SXI), an x-ray CCD camera, and the x-ray mirror assembly (XMA), a thin-foil-nested conically approximated Wolter-I optics. The SXI uses the P-channel, back-illuminated type CCD with an imaging area size of 31mm on a side. The four CCD chips are arranged in a 2×2 grid and can be cooled down to −120 °C with a single-stage Stirling cooler. The XMA nests thin aluminum foils coated with gold in a confocal way with an outer diameter of 45 cm. A pre-collimator is installed in front of the x-ray mirror for the reduction of the stray light. Combining the SXI and XMA with a focal length of 5.6m, a field of view of 38′ × 38′ over the energy range from 0.4 to 13 keV is realized. We have completed the fabrication of the flight model of both SXI and XMA. The performance verification has been successfully conducted in a series of sub-system level tests. We also carried out on-ground calibration measurements and the data analysis is ongoing.
A measurement called “local spot scan (LSS)” reveals the detailed local performance of the x-ray mirror assembly (XMA) of the XRISM satellite. A 6.4 keV 10 mm×10 mm pencil beam was tiled across the mirror aperture. We extracted three local performance metrics at each spot: effective area (EA), image shift, and image profile. The EA maps on the aperture of all the quadrants (QTs) are quantitatively very similar to each other. The inner region has two times larger local EA than the outer one because of the difference in reflectivity at shallower incident angles. The pattern of the image shift is different per QT. The pattern indicates systematic shifts of reflectors by the reflector alignment structures rather than random shifts, and most area of the XMA aperture has a longer focal length than the design. The image profile was quantified using the half power diameter (HPD). There is much less variation in the HPD maps than in the image shift. The inner region has better HPD because of its better conical approximation and figure error of the reflectors. Patterns visible in the HPD maps are associated with alignment structures at a certain radial range. The local performances acquired by the LSS will be compiled into the calibration data base (CalDB) files.
We present a summary of the ground calibration of the x-ray mirror assemblies (XMAs) for the XRISM satellite, that has been performed at the x-ray beamline at NASA’s Goddard Space Flight Center. We used a scan method with a narrow x-ray pencil beam to calibrate both Resolve and Xtend XMAs, at eight different energies. In this paper, we give an overview of the measurement setup, and show the resulting on-axis and off-axis effective area response. Results of imaging performance, stray light, and performance variation across the aperture will be presented in separate publications.
We describe an implementation of a broad-band soft X-ray polarimeter, substantially based on previous designs. The Globe-Orbiting Soft X-ray Polarimeter (GOSoX) is a SmallSat. As in a related mission concept the PiSoX Polarimeter, the grating arrangement is designed optimally for the purpose of polarimetry matching the dispersion of a spectrometer to a laterally graded multilayer (LGML). For GOSoX, the optics are lightweight Si mirrors in a one-bounce parabolic configuration. The instrument covers the wavelength range from 31 A to 75 A (165 - 400 eV). Upon satellite rotation, the intensities of the dispersed spectra, after reflection and polarizing by the LGMLs, give the three Stokes parameters needed to determine a source's linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe the potential scientific return and the proposed mission concept following the results of a JPL Team X concept study.
We describe a new implementation of a broad-band soft X-ray polarimeter, substantially based on a previous design. This implementation, the Pioneer Soft X-ray Polarimeter (PiSoX) is a SmallSat, designed for NASA’s call for Astrophysics Pioneers, small missions that could be CubeSats, balloon experiments, or SmallSats. As in REDSoX, the grating arrangement is designed optimally for the purpose of polarimetry with broad-band focussing optics by matching the dispersion of the spectrometer channels to laterally graded multilayers (LGMLs). The system can achieve polarization modulation factors over 90%. For PiSoX, the optics are lightweight Si mirrors in a one-bounce parabolic configuration. High efficiency, blazed gratings from opposite sectors are oriented to disperse to a LGML forming a channel covering the wavelength range from 35 Å to 75 Å (165 - 350 eV). Upon satellite rotation, the intensities of the dispersed spectra, after reflection and polarizing by the LGMLs, give the three Stokes parameters needed to determine a source’s linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe examples of the potential scientific return from instruments based on this design.
The XRISM X-ray observatory will fly two advanced instruments, the Resolve high-resolution spectrometer and the Xtend wide-field imager. These instruments, particularly Resolve, pose calibration challenges due to the unprecedented combination of spectral resolution, spectral coverage, and effective area, combined with a need to characterize the imaging fidelity of the full instrument system to realize the mission’s ambitious science goals. We present the status of the XRISM in-flight calibration plan, building on lessons from Hitomi and other X-ray missions. We present a discussion of targets and observing strategies to address the needed calibration measurements, with a focus on developing methodologies to plan a thorough and flexible calibration campaign and provide insight on calibration systematic error. We also discuss observations that exploit Resolve’s spectral
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.
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