We report a development status of a focal plane detector for the GEO-X (GEOspace X-ray imager) mission that will perform soft X-ray (≤2 keV) imaging spectroscopy of Earth’s magnetosphere from a micro satellite. The mission instrument consists of a microelectromechanical systems (MEMS) X-ray mirror and a focal plane detector. A sensor with fine positional resolution and moderate energy resolution in the energy band of 0.3 to 2 keV is required. Because the observing target is the magnetosphere around the day-side Earth, the visible-light background must be decreased by shortening the integration time for readout. To satisfy the above requirements, a high-speed X-ray CMOS sensor is being evaluated as a primary candidate for the detector. Irradiating the flight candidate sensor with monochromatic X-rays, we obtained the energy resolution of 205 eV (FWHM) at 6 keV by cooling the devices to −15°C. Radiation tolerance of the sensor, especially in terms of total dose effect, is investigated with 100 MeV proton. The amount of degradation of energy resolution is <50 eV up to 10 krad, which ensures that we will be able to track and calibrate the change of the line width in orbit.
GEOspace X-ray imager (GEO-X) is a small satellite mission aiming at visualization of the Earth’s magnetosphere by X-rays and revealing dynamic couplings between solar wind and the magnetosphere. In-situ spacecraft have revealed various phenomena in the magnetosphere. X-ray astronomy satellite observations recently discovered soft X-ray emissions originating from the magnetosphere. We are developing GEO-X by integrating innovative technologies of a wide field of view (FOV) X-ray instrument and a small satellite for deep space exploration. The satellite combines a Cubesat and a hybrid kick motor, which can produce a large delta v to increase the altitude of the orbit to about 30 to 60 RE from a relatively low-altitude (e.g., geo transfer orbit) piggyback launch. GEO-X carries a wide FOV (5 × 5 deg) and a good spatial resolution (10 arcmin) X-ray (0.3 to 2 keV) imaging spectrometer using a micro-machined X-ray telescope and a CMOS detector system combined with an optical blocking filter. We aim to launch the satellite around the solar maximum of solar cycle 25.
We have been developing an ultra-lightweight Wolter type-I X-ray telescope fabricated with micro electro mechanical systems (MEMS) technologies for GEO-X (GEOspace X-ray Imager) mission.
GEO-X will aim global imaging of the Earth's magnetosphere using X-rays.
The telescope is our original micropore optics which is light in weight (~5 g), compact with a short focal length (~250 mm), and has a wide field-of-view (~5 deg x 5 deg).
In this talk we show developed assembly processes to meet the requirements of the GEO-X mission and the telescope's X-ray imaging performance as an engineering model with this method.
We have been developing silicon foil X-ray optics using a hot plastic deformation process for future astronomical observations. Our foil mirror is made of a 0.3-mm thick silicon wafer and is plastically deformed into a high-accurate conical shape with a curvature radius of ~100 mm. The angular resolution we evaluated using a test sample mirror was ~32 arcseconds in the best region. We have also successfully coated a platinum film on the foil mirror using the atomic layer deposition process. In this talk, we report on the fabrication method and the X-ray imaging capability of our silicon foil X-ray optics.
GEO-X (GEOspace X-ray imager) is a small satellite mission aiming at visualization of the Earth’s magnetosphere by X-rays and revealing dynamical couplings between solar wind and magnetosphere. In-situ spacecraft have revealed various phenomena in the magnetosphere. In recent years, X-ray astronomy satellite observations discovered soft X-ray emission originated from the magnetosphere. We therefore develop GEO-X by integrating innovative technologies of the wide FOV X-ray instrument and the microsatellite technology for deep space exploration. GEO-X is a 50 kg class microsatellite carrying a novel compact X-ray imaging spectrometer payload. The microsatellite having a large delta v (<700 m/s) to increase an altitude at 40-60 RE from relatively lowaltitude (e.g., Geo Transfer Orbit) piggyback launch is necessary. We thus combine a 18U Cubesat with the hybrid kick motor composed of liquid N2O and polyethylene. We also develop a wide FOV (5×5 deg) and a good spatial resolution (10 arcmin) X-ray (0.3-2 keV) imager. We utilize a micromachined X-ray telescope, and a CMOS detector system with an optical blocking filter. We aim to launch the satellite around the 25th solar maximum.
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 are developing a novel Bragg reflection x-ray polarimeter using hot plastic deformation of silicon wafers. A Bragg reflection polarimeter has the advantage of simple principle and large modulation factor but suffers from the disadvantage of a narrow detectable energy band and difficulty to focus an incident beam. We overcome these disadvantages by bending a silicon wafer at high temperature. The bent Bragg reflection polarimeter have a wide energy band using different angles on the wafer and enable focusing. We have succeeded in measuring x-ray polarization with this method for the first time using a sample optic made from a 4-inch silicon (100) wafer.
We are developing an x-ray CMOS detector for the GEO-X (GEOspace x-ray imager) mission that will perform soft x-ray (≤2 keV) imaging spectroscopy of Earth’s magnetosphere using a micro satellite. The mission instrument consists of a MEMS x-ray mirror and a focal plane detector. For the latter, we need a sensor with fine positional resolution and moderate energy resolution in the energy band of 0.3 to 2 keV. Because we observe the day-side structure of the earth’s magnetosphere, visible-light background must be decreased by shortening the integration time for readout. To satisfy the above requirements, a high-speed x-ray CMOS sensor is being evaluated as a primary candidate for the detector. We adopt back-side illuminated sensors that have been originally developed for visible-light or UV imaging. The sensors have different specification in terms of the thickness of epitaxial wafer and specific resistance. Irradiating sensors with monochromatic x-rays from 55Fe, we obtained the energy resolution of 205 and 227 eV (FWHM) depending on the sensor type for single pixel events at 6 keV by cooling down the sensor to −15°C. On the other hand, we found that the pulse height of the events whose charges spread over multiple pixels are significantly lower than that of single pixel events in some chips. Then we selected the chips that shows better charge collection efficiency as flight candidate. Radiation tolerance of the sensor, especially in terms of total dose effect, is investigated with 100 MeV proton. The amount of dose ranges up to 100 krad depending on position in the sensor. In spite of the excessive dose compared with 10 krad/yr in the expected highly elliptical orbit, Mn Kα and Kβ are well resolved. The amount of degradation of energy resolution is less than 50 eV up to 10 krad, which ensures that we will be able to track and calibrate the change of the line width in orbit We also utilize multi-color x-rays to investigate spectroscopic performance in the energy band of 0.5 to 7 keV. Multiple lines below 1 keV are resolved and energy resolutions are evaluated as well as linearity performance.
We have been developing an ultra-lightweight Wolter type-I x-ray telescope fabricated with MEMS technologies for GEO-X (geospace x-ray imager) which is an 18U CubeSat (∼20 kg) to perform soft x-ray imaging spectroscopy of the entire Earth’s magnetosphere from Earth orbit near the moon. The telescope is our original micropore optics which possesses lightness (∼15 g), a short focal length (∼250 mm), and a wide field of view (∼5 ◦ × ∼5 ◦ ). The MEMS x-ray telescope is made of 4-inch Si (111) wafers. The Si wafer is firstly processed by deep reactive ion etching such that they have numerous curvilinear micropores (20-µm width) whose sidewalls are utilized as X-ray reflective mirrors. High-temperature hydrogen annealing and chemical mechanical polishing processes are then applied to make those sidewalls smooth and flat enough to reflect X-rays. After that, the wafer is plastic-deformed into a spherical shape and Pt-coated by plasma atomic layer deposition (ALD) process to focus x-rays with high reflectivity. Finally, we assemble two optics bent with different curvatures (1000- and 333-mm radius) into the Wolter type-I telescope. Optimizing the annealing and polishing processes, we found that the optic achieves an angular resolution of ∼5.4 arcmins in HPW. This is comparable with the requirement for GEO-X (∼5 arcmins in HPD at single reflection). Our optic was also successfully Pt-coated by a plasma-enhanced ALD process to enhance x-ray reflectivity. Moreover, we fabricated an STM telescope and confirmed its environmental tolerances by conducting an acoustic test with the H-IIA rocket qualification test level and a radiation tolerance test with a 100 MeV proton beam for 30 krad equivalent to a 3-year duration in the GEO-X orbit.
GEO-X is a small satellite mission in near moon orbit to visualize the Earth’s magnetosphere. Since the Earth is a bright x-ray source, its x-rays have a potentially effect on the GEO-X observations. Fluxes of the unexpected x-rays, stray lights, and of the GEO-X signal can be estimated. In order to estimate the stray light effect on the GEO-X FOV, we carried out a ray-tracing simulation and calculated the signal-to-noise ratio for elongations from the Earth. The S/N ratio shows a range depending on signal flux. The signal estimated by MHD simulations is smaller than estimation based on the typical observation. When we apply the small signal flux, the S/N ratio is <10 at 7 deg elongation of the GEO-X FOV from the Earth in an orbital altitude of 60RE. In order to improve the S/N ratio, there are two ways, installing a collimator in front of the optics and adjusting the observation position to obtain a large elongation. The ray-tracing simulation reveals that the collimator with 30 µm pore width and 300 µm thickness can improve the S/N ratio. The S/N ratio with the collimator can achieve >10 when the elongation is 7 deg in the orbital altitude of 60 RE. A sample collimator was fabricated by a Si dry etching. Difference of the pore width from the designed value was occurred. Since the difference can lead to extra photon loss, a trade-off study between fabrication precision and observation position is important.
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.
We report development status of an X-ray imaging spectrometer for scientific micro satellite mission GEO-X that aims for imaging of Earth’s magnetosphere from the vicinity of the Moon (∼40 RE). The planned direction for the observations includes proximity of the day-side Earth. Therefore the primary requirement for the detector is the fast frame rate to decrease the visible light background. In this regard we will apply complementary MOS (CMOS) sensor that is originally fabricated for the visible light and/or infrared spectroscopy. Faster readout speed improves time resolution and decrease the contribution from visible light compared with the conventional CCD detectors. We evaluate imaging and spectroscopic performances of backside illumination type scientific CMOS sensors with low noise performance. Most of the signals produced by X-rays distributes within 2 by 2 pixels. Spectra of monochromatic X-rays exhibit significant difference of pulse height between the event within single pixel and that spreads across multiple pixels, which indicates that a part of the signal charges are lost around the pixel edges. Then we adopt another type of the sensor that have been updated in terms of the incident surface treatment. We found that the amount of the lost charges are substantially decreased with the new sensor. Another measure to improve the spectroscopic performance is the dark level determination. Gradual or discontinuous change of the dark level in orbit might it difficult to evaluate the appropriate dark level especially for the high frame rate and the limited resources of onboard computer. Then we take the average of pulse heights for the outermost pixels in a event (5 by 5 pixels) and correct the pulse height of all pixels with the average value. With these measures the energy resolution improved successfully.
GEO-X (GEOspace X-ray imager) is a 50 kg-class small satellite to image the global Earth’s magnetosphere in X-rays via solar wind charge exchange emission. A 12U CubeSat will be injected into an elliptical orbit with an apogee distance of ∼40 Earth radii. In order to observe the diffuse soft X-ray emission in 0.3-2 keV and to verify X-ray imaging of the dayside structures of the magnetosphere such as cusps, magnetosheaths and magnetopauses which are identified statistically by in-situ satellite observations, an original light-weight X-ray imaging spectrometer (∼10 kg, ∼10 W, ∼10×10×30 cm) will be carried. The payload is composed of a ultra light-weight MEMS Wolter type-I telescope (∼4×4 deg2 FOV, <10 arcmin resolution) and a high speed CMOS sensor with a thin optical blocking filter (∼2×2 cm2 , frame rate ∼20 ms, energy resolution <80 eV FWHM at 0.6 keV). An aimed launch year is 2023-25 corresponding to the 25th solar maximum.
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 source position determination method of the multiplexing lobster-eye optics (MuLE), which is a newly proposed configuration of the Lobster-Eye (LE) optics to reduce the number of focal plane detectors significantly, was developed. In the MuLE configuration, X-rays came from different field-of-views (FoVs) were focused on a single imager. To separate the multiplexed FoVs, the optics was designed so that cross-like responses of LE mirror in different FoVs had different azimuthal rotation angles. In this paper, we show the method to determine the rotation angles and verify the FoV discrimination power by using a ray tracing simulation. The configuration we assumed in the simulation was nine multiplexed FoVs projecting onto a single imager (nine-segment MuLE optics) with a 30 cm focal length and a 9×9 cm2 effective area of each LE segment. One LE segment covers 9.6°× 9.6° FoV and the total FoV of the nine-segment MuLE configuration was 9 times of that. Our method provided 100% correct FoV discrimination at the 5σ detection limit flux (35–70 mCrab) for a transient source with a duration of 100 s except for the edge of the FoV.
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 propose a concept of multiplexing lobster-eye (MuLE) optics to achieve significant reductions in the number of focal plane imagers in lobster-eye (LE) wide-field x-ray monitors. In the MuLE configuration, an LE mirror is divided into several segments and the x-rays reflected on each of these segments are focused on a single image sensor in a multiplexed configuration. If each LE segment assumes a different rotation angle, the azimuthal rotation angle of a cross-like image reconstructed from a point source by the LE optics identifies the specific segment that focuses the x-rays on the imager. With a focal length of 30 cm and LE segments with areas of 10 × 10 cm2, ∼1 sr of the sky can be covered with 36 LE segments and only four imagers (with total areas of 10 × 10 cm2). A ray tracing simulation was performed to evaluate the nine-segment MuLE configuration. The simulation showed that the flux (0.5 to 2 keV) associated with the 5σ detection limit was ∼2 × 10 − 10 erg cm − 2 s − 1 (10 mCrab) for a transient with a duration of 100 s. The simulation also showed that the direction of the transient for flux in the range of 14 to 17 mCrab at 0.6 keV was determined correctly with a 99.7% confidence limit. We conclude that the MuLE configuration can become an effective on-board device for small satellites for future x-ray wide-field transient monitoring.
Toward an era of x-ray astronomy, next-generation x-ray optics are indispensable. To meet a demand for telescopes lighter than the foil optics but with a better angular resolution <1 arcmin, we are developing micropore x-ray optics based on micromaching technologies. Using sidewalls of micropores through a thin silicon wafer, this type can be the lightest x-ray telescope ever achieved. Two Japanese missions, ORBIS and GEO-X, will carry this telescope. ORBIS is a small x-ray astronomy mission to monitor supermassive blackholes, while GEO-X is a small exploration mission of the Earth’s magnetosphere. Both missions need an ultralightweight (<1 kg) telescope with moderately good angular resolution (<10 arcmin) at an extremely short focal length (<30 cm). We plan to demonstrate this type of telescope in these two missions around 2020.
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.
We describe the development of the focal plane detector onboard a micro-satellite aimed for observing cosmic Xray emission. Combined with an X-ray optics with focal length of approximately 40 mm, an X-ray CCD camera realizes low and stable background thanks to its capability of event classification by pulse height distribution of a event. The mission will intensively monitor a specific binary black hole to investigate periodic time variability owing to its possible binary motion. The focal plane detector adopts P-channel back-illumination type CCD. It is a miniature version of the sensors utilized in the CCD camera aboard Hitomi satellite but is upgraded in terms of the energy resolution and the prevention of visible light transmittance. We have built up an equipment for cooling and driving the device. Dark current as a function of device temperature is investigated. We see clear difference of the amount of the dark current between the imaging area and frame store area, which is probably due to the difference of the pixel size. The result indicates sufficiently low dark current can be achieved with temperature lower or equal to -80 °C. Number of pinholes in a surface aluminium layer is significantly different between devices. We identified a process with which we decrease the number of pinholes. To realize a whole instrument, we develop communication board and compact analog board.
Toward a new era of X-ray astronomy, next generation X-ray optics are indispensable. To meet a demand for telescopes lighter than the foil optics but with a better angular resolution less than 1 arcmin, we are developing micropore X-ray optics based on micromaching technologies. Using sidewalls of micropores through a thin silicon wafer, this type can be the lightest X-ray telescope ever achieved. Two new Japanese missions ORBIS and GEOX will carry this optics. ORBIS is a small X-ray astronomy mission to monitor supermassive blackholes, while GEO-X is a small exploration mission of the Earth’s magnetosphere. Both missions need a ultra light-weight (<1 kg) telescope with moderately good angular resolution (<10 arcmin) at an extremely short focal length (<30 cm). We plan to demonstrate this optics in these two missions around 2020, aiming at future other astronomy and exploration missions.
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.
The soft x-ray spectrometer (SXS) was a cryogenic high-resolution x-ray spectrometer onboard the Hitomi (ASTRO-H) satellite that achieved energy resolution of 5 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator (ADR). The cooling chain from room temperature to the ADR heat sink was composed of two-stage Stirling cryocoolers, a He4 Joule–Thomson cryocooler, and superfluid liquid helium and was installed in a dewar. It was designed to achieve a helium lifetime of more than 3 years with a minimum of 30 L. The satellite was launched on February 17, 2016, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the helium tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and the cryocoolers.
We summarize all of the in-orbit operations of the soft x-ray spectrometer (SXS) onboard the ASTRO-H (Hitomi) satellite. The satellite was launched on February 17, 2016, and the communication with the satellite ceased on March 26, 2016. The SXS was still in the commissioning phase, in which the set-ups were progressively changed. This paper is intended to serve as a concise reference of the events in orbit in order to properly interpret the SXS data taken during its short lifetime and as a test case for planning the in-orbit operation for future microcalorimeter missions.
When using superfluid helium in low-gravity environments, porous plug phase separators are commonly used to vent boil-off gas while confining the bulk liquid to the tank. Invariably, there is a flow of superfluid film from the perimeter of the porous plug down the vent line. For the soft x-ray spectrometer onboard ASTRO-H (Hitomi), its approximately 30-liter helium supply has a lifetime requirement of more than 3 years. A nominal vent rate is estimated as ∼30 μg/s, equivalent to ∼0.7 mW heat load. It is, therefore, critical to suppress any film flow whose evaporation would not provide direct cooling of the remaining liquid helium. That is, the porous plug vent system must be designed to both minimize film flow and to ensure maximum extraction of latent heat from the film. The design goal for Hitomi is to reduce the film flow losses to <2 μg/s, corresponding to a loss of cooling capacity of <40 μW. The design adopts the same general design as implemented for Astro-E and E2, using a vent system composed of a porous plug, combined with an orifice, a heat exchanger, and knife-edge devices. Design, on-ground testing results, and in-orbit performance are described.
The soft x-ray spectrometer (SXS) onboard the Hitomi satellite achieved a high-energy resolution of ∼4.9 eV at 6 keV with an x-ray microcalorimeter array cooled to 50 mK. The cooling system utilizes liquid helium, confined in zero gravity by means of a porous plug (PP) phase separator. For the PP to function, the helium temperature must be kept lower than the λ point of 2.17 K in orbit. To determine the maximum allowable helium temperature at launch, taking into account the uncertainties in both the final ground operations and initial operation in orbit, we constructed a thermal mathematical model of the SXS dewar and PP vent and carried out time-series thermal simulations. Based on the results, the maximum allowable helium temperature at launch was set at 1.7 K. We also conducted a transient thermal calculation using the actual temperatures at launch as initial conditions to determine flow and cooling rates in orbit. From this, the equilibrium helium mass flow rate was estimated to be ∼34 to 42 μg/s, and the lifetime of the helium mode was predicted to be ∼3.9 to 4.7 years. This paper describes the thermal model and presents simulation results and comparisons with temperatures measured in the orbit.
KEYWORDS: X-rays, Sensors, Spectroscopy, Space operations, Lithium, Field effect transistors, Satellites, Calibration, Single crystal X-ray diffraction, Magnetic sensors
We present the overall design and performance of the Astro-H (Hitomi) Soft X-Ray Spectrometer (SXS). The instrument uses a 36-pixel array of x-ray microcalorimeters at the focus of a grazing-incidence x-ray mirror Soft X-Ray Telescope (SXT) for high-resolution spectroscopy of celestial x-ray sources. The instrument was designed to achieve an energy resolution better than 7 eV over the 0.3-12 keV energy range and operate for more than 3 years in orbit. The actual energy resolution of the instrument is 4-5 eV as demonstrated during extensive ground testing prior to launch and in orbit. The measured mass flow rate of the liquid helium cryogen and initial fill level at launch predict a lifetime of more than 4 years assuming steady mechanical cooler performance. Cryogen-free operation was successfully demonstrated prior to launch. The successful operation of the SXS in orbit, including the first observations of the velocity structure of the Perseus cluster of galaxies, demonstrates the viability and power of this technology as a tool for astrophysics.
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 2016 February 17, the spacecraft lost its function on 2016 March 26, but the commissioning phase for about a month provided valuable information on the on-board 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.
The Soft X-ray Spectrometer (SXS) is a cryogenic high-resolution X-ray spectrometer onboard the ASTRO-H satellite, that achieves energy resolution better than 7 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator. The cooling chain from room temperature to the ADR heat sink is composed of 2-stage Stirling cryocoolers, a 4He Joule-Thomson cryocooler, and super uid liquid He, and is installed in a dewar. It is designed to achieve a helium lifetime of more than 3 years with a minimum of 30 liters. The satellite was launched on 2016 February 17, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the He tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and cryocoolers.
DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for a launch around 2022 with JAXA’s Epsilon rocket. Its main aim is a search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy of redshifted emission lines from OVII and OVIII ions. The superior energy resolution of TES microcalorimeters combined with a wide field of view (30' diameter) will enable us to look into gas dynamics of cosmic plasmas in a wide range of spatial scales from Earth’s magnetosphere to unvirialized regions of clusters of galaxies. Mechanical and thermal design of the spacecraft and development of the TES calorimeter system are described. Employing an enlarged X-ray telescope with a focal length of 1.2 m and fast repointing capability, DIOS can observe absorption features from X-ray afterglows of distant gamma-ray bursts.
We summarize all the in-orbit operations of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H (Hit- omi) satellite. The satellite was launched on 2016/02/17 and the communication with the satellite ceased on 2016/03/26. The SXS was still in the commissioning phase, in which the setups were progressively changed. This article is intended to serve as a reference of the events in the orbit to properly interpret the SXS data taken during its short life time, and as a test case for planning the in-orbit operation for future micro-calorimeter missions.
Suppression of super fluid helium flow is critical for the Soft X-ray Spectrometer onboard ASTRO-H (Hitomi). In nominal operation, a small helium gas flow of ~30 μg/s must be safely vented and a super fluid film flow must be sufficiently small <2 μg/s. To achieve a life time of the liquid helium, a porous plug phase separator and a film flow suppression system composed of an orifice, a heat exchanger, and knife edge devices are employed. In this paper, design, on-ground testing results and in-orbit performance of the porous plug and the film flow suppression system are described.
The Soft X-ray Spectrometer (SXS) onboard ASTRO-H (Hitomi) achieved a high energy resolution of ~ 4.9 eV at 6 keV with an X-ray microcalorimeter array kept at 50 mK in the orbit. The cooling system utilizes liquid helium, and a porous plug phase separator is utilized to confine it. Therefore, it is required to keep the helium temperature always lower than the λ point of 2.17 K in the orbit. To clarify the maximum allowable helium temperature at the launch also considering the uncertainties of the initial operation in the orbit, we constructed a thermal mathematical model of the SXS dewar which properly implements the helium mass flow rate through the porous plug, and carried out time-series thermal simulations. Based on the results, the maximum allowable helium temperature at the launch was set at 1.7 K. We also conducted a transient thermal calculation using the actual temperatures at the launch as initial conditions. As a result, the helium mass flow rate when the helium temperature was in equilibrium is estimated to be 34–42 μg/s, and the life time of the helium mode is predicted to be ~ 3.9–4.7 years. The present paper reports model structures, simulation results, and the comparisons with temperatures measured in the orbit.
DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for a launch around 2020 with JAXA’s Epsilon rocket. Its main aim is a search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy of redshifted emission lines from OVII and OVIII ions. The superior energy resolution of TES microcalorimeters combined with a very wide field of view (30–50 arcmin diameter) will enable us to look into gas dynamics of cosmic plasmas in a wide range of spatial scales from Earth’s magnetosphere to unvirialized regions of clusters of galaxies. Mechanical and thermal design of the spacecraft and development of the TES calorimeter system are described. We also consider revising the payload design to optimize the scientific capability allowed by the boundary conditions of the small mission.
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of ΔE ≤ 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.
We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.
DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small scientific satellite with the main aim of searching warm-hot intergalactic medium using redshifted OVII and OVIII lines. The wide-field spectroscopic capability of DIOS will also bring rich science about the dynamics of cosmic hot plasmas in all spatial scales. The instrument will consist of a 4-stage X-ray telescope and an array of TES microcalorimeters with up to 400 pixels, cooled with mechanical coolers. Hardware development of DIOS and outstanding issues about the payload are described. DIOS will be further developed with international collaboration and will be proposed to the earliest call of JAXA’s small scientific satellite series.
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated
by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the highenergy
universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV.
These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3–12 keV with
high spectral resolution of ΔE ≦ 7 eV, enabled by a micro-calorimeter array located in the focal plane of
thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5–80 keV, located in the focal plane of
multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4–12 keV,
with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera
type soft gamma-ray detector, sensitive in the 40–600 keV band. The simultaneous broad bandpass, coupled
with high spectral resolution, will enable the pursuit of a wide variety of important science themes.
One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three
missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This
instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition
Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The
array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena.
In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given.
Our development of ultra light-weight X-ray micro pore optics based on MEMS (Micro Electro Mechanical System)
technologies is described. Using dry etching or X-ray lithography and electroplating, curvilinear sidewalls
through a flat wafer are fabricated. Sidewalls vertical to the wafer surface are smoothed by use of high temperature
annealing and/or magnetic field assisted finishing to work as X-ray mirrors. The wafer is then deformed to
a spherical shape. When two spherical wafers with different radii of curvature are stacked, the combined system
will be an approximated Wolter type-I telescope. This method in principle allows high angular resolution and
ultra light-weight X-ray micro pore optics. In this paper, performance of a single-stage optic, coating of a heavy
metal on sidewalls with atomic layer deposition, and assembly of a Wolter type-I telescope are reported.
Microelectromechanical systems (MEMS) micropore X-ray optics were proposed as an ultralightweight, high-
resolution, and low cost X-ray focusing optic alternative to the large, heavy and expensive optic systems in
use today. The optic's monolithic design which includes high-aspect-ratio curvilinear micropores with minimal
sidewall roughness is challenging to fabricate. When made by either deep reactive ion etching or X-ray LIGA, the
micropore sidewalls (re
ecting surfaces) exhibit unacceptably high surface roughness. A magnetic eld-assisted
nishing (MAF) process was proposed to reduce the micropore sidewall roughness of MEMS micropore optics
and improvements in roughness have been reported. At this point, the best surface roughness achieved is 3
nm Rq on nickel optics and 0.2 nm Rq on silicon optics. These improvements bring MEMS micropore optics
closer to their realization as functional X-ray optics. This paper details the manufacturing and post-processing
of MEMS micropore X-ray optics including results of recent polishing experiments with MAF.
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated
by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the
high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular
resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination
of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray
mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV)
provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD
camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray
detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led
by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of
ΔE ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be
pursued.
The Soft X-ray Spectrometer (SXS) is a cryogenic high resolution X-ray spectrometer onboard the X-ray astronomy
satellite ASTRO-H. The detector array is cooled down to 50 mK using a 3-stage adiabatic demagnetization
refrigerator (ADR). The cooling chain from room temperature to the ADR heat-sink is composed of superfluid
liquid He, a 4He Joule-Thomson cryocooler, and 2-stage Stirling cryocoolers. It is designed to keep 30 L of liquid
He for more than 3 years in the nominal case. It is also designed with redundant subsystems throughout from
room temperature to the ADR heat-sink, to alleviate failure of a single cryocooler or loss of liquid He.
DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small scientific satellite with a main aim for the search of warm-hot intergalactic medium using redshifted OVII and OVIII lines. The instrument will consist of a 4-stage X-ray telescope and an array of TES microcalorimeters with 256 pixels, cooled with mechanical coolers.
Hardware development of DIOS and the expected results are described. Survey observations over about 5° x 5° area will reveal new filamentary structures. DIOS will be proposed to the 3rd mission in JAXA's small satellite series in 2011, aiming for launch around 2016 if it will be selected.
One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the
X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is
based on X-ray micro-calorimeters with Transition Edge Sensor thermometers. The pixels have metallic X-ray absorbers
and are read-out by multiplexed SQUID electronics. The requirements for this instrument are demanding. In the central
array (40 x 40 pixels) an energy resolution of < 2.5 eV is required, whereas the energy resolution of the outer array is
more relaxed (≈ 10 eV) but the detection elements have to be a factor 16 larger in order to keep the number of read-out
channels acceptable for a cryogenic instrument. Due to the large collection area of the IXO optics, the XMS instrument
must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In
addition, an anti-coincidence detector is required to suppress the particle-induced background.
In this paper we will summarize the instrument status and performance. We will describe the results of design studies for
the focal plane assembly and the cooling systems. Also the system and its required spacecraft resources will be given.
We present the science and an overview of the Soft X-ray Spectrometer onboard the ASTRO-H mission with
emphasis on the detector system. The SXS consists of X-ray focusing mirrors and a microcalorimeter array and
is developed by international collaboration lead by JAXA and NASA with European participation. The detector
is a 6×6 format microcalorimeter array operated at a cryogenic temperature of 50 mK and covers a 3' ×3' field
of view of the X-ray telescope of 5.6 m focal length. We expect an energy resolution better than 7 eV (FWHM,
requirement) with a goal of 4 eV. The effective area of the instrument will be 225 cm2 at 7 keV; by a factor of
about two larger than that of the X-ray microcalorimeter on board Suzaku. One of the main scientific objectives
of the SXS is to investigate turbulent and/or macroscopic motions of hot gas in clusters of galaxies.
In recent years, X-ray telescopes have been shrinking in both size and weight to reduce cost and volume on
space flight missions. Current designs focus on the use of MEMS technologies to fabricate ultra-lightweight and
high-resolution X-ray optics. In 2006, Ezoe et al. introduced micro-pore X-ray optics fabricated using anisotropic
wet etching of silicon (110) wafers. These optics, though extremely lightweight (completed telescope weight 1
kg or less for an effective area of 1000 cm2), had limited angular resolution, as the reflecting surfaces were flat
crystal planes. To achieve higher angular resolution, curved reflecting surfaces should be used.
Both silicon dry etching and X-ray LIGA were used to create X-ray optics with curvilinear micro-pores;
however, the resulting surface roughness of the curved micro-pore sidewalls did not meet X-ray reflection criteria
of 10 nm rms in a 10 μm2 area. This indicated the need for a precision polishing process. This paper describes
the development of an ultra-precision polishing process employing an alternating magnetic field assisted finishing
process to polish the micro-pore side walls to a mirror finish (< 4 nmrms). The processing principle is presented,
and a polishing machine is designed and fabricated to explore the feasibility of this polishing process as a possible
method for processing MEMS X-ray optics to meet X-ray reflection specifications.
We report on our development of hot plastic deformation of silicon wafer for high-resolution and light-weight
X-ray optics. The highly polished silicon wafer with an excellent flat surface is a promising candidate for the
next generation space X-ray telescopes. Deformation accuracy and stability, especially if elastic deformation
is used, are issues. The hot plastic deformation of the silicon wafer allows us 3-dimensional shaping without
spring back after the deformation. As a first step of R & D, we conducted the hot plastic deformation of 4-inch
silicon (111) wafers with a thickness of 300 μm by using hemispherical dies with a curvature radius of 1000 mm.
The deformed wafer kept good surface quality but showed a slightly large curvature of 1030 mm. We measured
the X-ray reflectivity of the deformed wafer at Al Kα 1.49 keV. For the first time, we detected the total X-ray
reflection on the deformed wafer. Estimated rms surface roughness was 0-1 nm and no significant degradation
from the bare silicon wafers was seen.
We have been developing ultra light-weight X-ray optics using MEMS (Micro Electro Mechanical Systems)
technologies.We utilized crystal planes after anisotropic wet etching of silicon (110) wafers as X-ray mirrors and
succeeded in X-ray reflection and imaging. Since we can etch tiny pores in thin wafers, this type of optics can
be the lightest X-ray telescope. However, because the crystal planes are alinged in certain directions, we must
approximate ideal optical surfaces with flat planes, which limits angular resolution of the optics on the order of
arcmin. In order to overcome this issue, we propose novel X-ray optics based on a combination of five recently
developed MEMS technologies, namely silicon dry etching, X-ray LIGA, silicon hydrogen anneal, magnetic fluid
assisted polishing and hot plastic deformation of silicon. In this paper, we describe this new method and report
on our development of X-ray mirrors fabricated by these technologies and X-ray reflection experiments of two
types of MEMS X-ray mirrors made of silicon and nickel. For the first time, X-ray reflections on these mirrors
were detected in the angular response measurements. Compared to model calculations, surface roughness of the
silicon and nickel mirrors were estimated to be 5 nm and 3 nm, respectively.
Our recent development of transition-edge sensor (TES) microcalorimeters for future X-ray astronomical missions
such as DIOS is reported. In-house micromaching processes has been established aiming at prompt fabrication
of TES devices. With a single-pixel TES microcalorimeter and an Au absorber, the energy resolution of 4.8 eV
at 5.9 keV is achieved. 16×16 pixel arrays of TES microcalorimeters are successfully fabricated by using deep
dry etching technique. The energy resolution is 11 eV and 26 eV with and without an Au absorber, respectively.
The worse energy resolution than a single-pixel TES is due to large decrease of TES sensitivity and increase
of transition temperature after etching. The reason for these phenomena is under investigation. In parallel,
mushroom-type Au absorber structures are being tested. Furthermore, to precisely measure TES sensitivities
and heat capacity, an experimental setup for impedance measurements is established.
We present the current status of a small X-ray mission DIOS (Diffuse Intergalactic Oxygen Surveyor), consisting
of a 4-stage X-ray telescope and an array of TES microcalorimeters, cooled with mechanical coolers, with a total
weight of about 400 kg. The mission will perform survey observations of warm-hot intergalactic medium using
OVII and OVIII emission lines, with the energy coverage up to 1.5 keV. The wide field of view of about 50'
diameter, superior energy resolution close to 2 eV FWHM, and very low background will together enable us a
wide range of science for diffuse X-ray sources. We briefly describe the current status of the development of the
satellite, and the subsystems.
KEYWORDS: X-rays, Sensors, Mirrors, Signal to noise ratio, Spectral resolution, Plasmas, Galaxy groups and clusters, Temperature metrology, Ionization, Iron
Spatially resolved X-ray spectroscopy with high spectral resolution allows the study of astrophysical processes in
extended sources with unprecedented sensitivity. This includes the measurement of abundances, temperatures, densities,
ionisation stages as well as turbulence and velocity structures in these sources. An X-ray calorimeter is planned for the
Russian mission Spektr Röntgen-Gamma (SRG), to be launched in 2011. During the first half year (pointed phase) it will
study the dynamics and composition of of the hot gas in massive clusters of galaxies and in supernova remnants (SNR).
During the survey phase it will produce the first all sky maps of line-rich spectra of the interstellar medium (ISM).
Spectral analysis will be feasible for typically every 5° x 5° region on the sky. Considering the very short time-scale for
the development of this instrument it consists of a combination of well developed systems. For the optics an extra
eROSITA mirror, also part of the Spektr-RG payload, will be used. The detector will be based on spare parts of the
detector flown on Suzaku combined with a rebuild of the electronics and the cooler will be based on the design for the
Japanese mission NeXT. In this paper we will present the science and give an overview of the instrument.
The Soft X-ray Spectrometer (SXS) onboard the NeXT (New exploration X-ray Telescope) is an X-ray spectrometer
utilizing an X-ray microcalorimeter array. Combined with the soft X-ray telescope of 6 m focal length,
the instrument will have a ~ 290cm2 effective at 6.7 keV. With the large effective area and the energy resolution
as good as 6 eV (FWHM), the instrument is very suited for the high-resolution spectroscopy of iron K emission
line. One of the major scientific objectives of SXS is to determine turbulent and/or macroscopic motions of the
hot gas in clusters of galaxies of up to z ~ 1. The instruments will use 6 × 6 or 8 × 8 format microcalorimeter
array which is similar to that of Suzaku XRS. The detector will be cooled to a cryogenic temperature of 50 mK
by multi-stage cooling system consisting of adiabatic demagnetization refrigerator, super fluid He, a 3He Joule
Thomson cooler, and double-stage stirling cycle cooler.
The SXS (Soft X-ray Spectrometer) onboard the coming Japanese X-ray satellite NeXT (New Exploration Xray
Telescope) and the SXC (Spectrum-RG X-ray Calorimeter) in Spectrum-RG mission are microcalorimeter
array spectrometers which will achieve high spectral resolution of ~ 6 eV in 0.3-10.0 keV energy band. These
spectrometers are well-suited to address key problems in high-energy astrophysics. To achieve these high spectral
sensitivities, these detectors require to be operated under 50 mK by using very efficient cooling systems including
adiabatic demagnetization refrigerator (ADR). For both missions, we propose a two-stage series ADR as a cooling
system below 1 K, in which two units of ADR consists of magnetic cooling material, a superconducting magnet,
and a heat switch are operated step by step. Three designs of the ADR are proposed for SXS/SXC. In all three
designs, ADR can attain the required hold time of 23 hours at 50 mK and cooling power of 0.4μW with a low
magnetic fields (1.5/1.5 Tesla or 2.0/3.0 Tesla) in a small configuration (180 mmφ× 319 mm in length).
We also fabricated a new portable refrigerator for a technology investigation of two-stage ADR. Two units of
ADR have been installed at the bottom of liquid He tank. By using this dewar, important technologies such as an operation of two-stage cooling cycle, tight temperature control less than 1 μK (in rms) stability, a magnetic
shielding, saltpills, and gas-gap heat switches are evaluated.
How structures of various scales formed and evolved from the early Universe up to present time is a fundamental
question of astrophysics. EDGE will trace the cosmic history of the baryons from the early generations of massive
stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low
redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing
gravitational collapse by dark matter (the so-called warm hot intragalactic medium). In addition EDGE, with its
unprecedented capabilities, will provide key results in many important fields. These scientific goals are feasible with a
medium class mission using existing technology combined with innovative instrumental and observational capabilities
by: (a) observing with fast reaction Gamma-Ray Bursts with a high spectral resolution (R ~ 500). This enables the study
of their (star-forming) environment and the use of GRBs as back lights of large scale cosmological structures; (b)
observing and surveying extended sources (galaxy clusters, WHIM) with high sensitivity using two wide field of view
X-ray telescopes (one with a high angular resolution and the other with a high spectral resolution). The mission concept
includes four main instruments: a Wide-field Spectrometer with excellent energy resolution (3 eV at 0.6 keV), a Wide-
Field Imager with high angular resolution (HPD 15") constant over the full 1.4 degree field of view, and a Wide Field
Monitor with a FOV of 1/4 of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response
up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part
of the Cosmic Vision call. We will briefly review the science drivers and describe in more detail the payload of this
mission.
The first light of a ultra-lightweight and low-cost micro-pore X-ray optic utilizing MEMS (Micro Electro Mechanical
Systems) technologies is reported. Our idea is to use silicon (111) planes appeared after anisotropic wet
etching of silicon wafers. As a first step to Wolter type-1 optics, a single-stage optic with a focal length of 750
mm and a diameter of 100 mm was designed for energies below 2 keV. The optic consists of 218 mirror chips
for X-ray reflection and an optic mount for packing these chips. Design parameters and required fabrication
accuracies were determined with numerical simulations. The fabricated optic satisfied these accuracies and its
imaging quality was measured at the ISAS X-ray beam line at Al Kα 1.49 keV. A focused image was successfully
obtained. The measured image size of ~4 mm was consistent with the chip sizes. The estimated X-ray reflectivity
also could be explained by micro-roughness of less than 3 nm and geometrical occulting effect due to large
obstacle structures on the reflection surface.
Recent development of the extremely light-weight micro pore optics based on the semiconductor MEMS (Micro Electro Mechanical System) technologies is reported. Anisotropic chemical wet etching of silicon (110) wafers were utilized, in order to obtain a row of smooth (111) side walls vertical to the wafer face and to use them as X-ray mirrors. To obtain high performance mirrors with smooth surfaces and a high aspect ratio, several modifications were made to our previous manufacturing process shown in Ezoe et al. (2005). After these improvements, smooth surfaces with rms roughness of the order of angstroms and also a high aspect ratio of 20 were achieved. Furthermore, a single-stage optic was designed as a first step to multi-stage optics. A mounting device and a slit device for the sample optic were fabricated fully using the MEMS technologies and evaluated.
Development of a new light-weight and low-cost micro pore optics is reported. Utilizing anisotropic chemical wet etching of MEMS (Micro Electro Mechanical System) technology, a number of smooth sidewalls are obtained at once. These sidewalls are potential X-ray mirrors. As a first step of R&D, basic characters of sidewalls such as surface roughness and X-ray reflectivity are experimentally studied. Rms-roughness of 10 ~ 20Å is confirmed in a KOH-etched wafer. Furthermore, the X-ray reflection is for the first time detected at Mg Kα 1.25 keV. Based on the obtained results, numerical simulations of four-stage MEMS X-ray optics are performed for future satellite mission.
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