We are developing monolithic active pixel sensors, x-ray SOIPIXs based on a Silicon-On-Insulator CMOS technology. Its event trigger output function offers a high time resolution better than ~10 usec. (1) In 2022-23, we and evaluated large sensors, XRPIX-X, with a pixel array size of 14mm x 22mm. We report its design and the results of the performance evaluation. (2) We are developing "Digital X-ray SOIPIXs" for satellite use, featuring on-chip ADCs, DACs, and BGRs for noise robustness. An on-chip clock pattern generator is also included to simplify the readout digital circuits. (3) XRPIXs are increasingly being utilized in various scientific applications beyond x-ray astronomy, and a brief introduction will be provided.
Current x-ray astronomical satellites carry CCD cameras that have moderate performance in imaging, spectroscopy and timing. Future x-ray telescopes with large effective areas and sharp point spread functions require quick readout of focal plane sensors to realize imaging spectroscopy without photon pile-up nor intermittency of exposure time. To fulfill the requirements we are developing a hybrid sensor of CCD and CMOS. The former has readout nodes for every columns and the latter equips corresponding readout ICs including analog-to-digital converters. Both parts are implemented in the same package. Vertical transfer frequency of 100kHz enables us to readout the whole frame within 10ms even with 1k by 1k pixel format. Our first test device with pixel format of 128×1024 and pixel size of 11μm square has been evaluated with monochromatic x-rays from 109Cd. X-ray events are successfully detected and the energy resolution is 1.43keV (full width at half maximum) at 22keV for the events whose signal charges are concentrated in a single pixel. Approximately 30% of charges are lost for the multi-pixel events, which implies that there might exist non-depleted region in the wafer. Pulse height comparison among the split pattern of the events indicated non-uniformity of the electric field in horizontal axis. As a next step We will adopt the CCD wafer that has been used for XRISM/Xtend in order to realize the optimum electric field.
We are developing a complementary metal oxide semiconductor (CMOS) camera to be onboard GEO-X (GEOspace X-ray imager) microsatellite. The GEO-X mission observes soft X-rays produced by Solar Wind Charge eXchange (SWCX), in which ions in the solar wind collide with atoms in the Earth’s exosphere and steal electrons, to visualize the day-side magnetospheric boundary. The payload of the satellite is approximately 3U (∼ L 10 cm ×W 10 cm × H 30 cm) in size and approximately 10 kg in mass and consists of the X-ray telescope and a focal plane detector. A back-side illuminated CMOS sensor is placed on the focal plane of the X-ray telescope, and the optical blocking filter is used for high-sensitivity imaging spectroscopy of X-rays from 0.3−2.0 keV. The design and fabrication of the printed circuit boards for housekeeping data collection and the housing assembly are also ongoing. We implement our own on-board event extraction logic to achieve data acquisition at 48 fps without any data loss. In addition, we performed functional testing of a digital processing board using SoC (Zynq) and its radiation tolerance investigation and found that the pedestal level is stable even when irradiated Zynq with 100 MeV/u protons. Furthermore, we irradiated the sensor cooled to −35 °C with polychromatic X-rays of 0.5 − 7.0 keV to evaluate the spectral performance of the sensor. The energy resolution is found to be 120 eV (FWHM) at 0.6 keV and the lower edge of the effective energy range is below 300 eV.
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.
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.
GEO-X (GEOspace X-ray imager) is a small satellite mission to visualize the Earth’s magnetosphere through Solar Wind Charge eXchange (SWCX). SWCX is known as soft X-ray emissions generated by the charge exchange between highly charged-state heavy ions and neutral atoms in the Earth’s exosphere. The GEO-X satellite is aimed to be launched during the upcoming solar maximum around 2025-2027 and is planned to be injected to a low-latitude orbit which allows visualization of the magnetosphere from outside the magnetosphere. The satellite will carry a light-weight X-ray imaging spectrometer, dramatically improving the size and weight of those onboard past X-ray astronomy satellites.
The Soft X-ray Imager (SXI) is an X-ray CCD camera of the Xtend system onboard the X-Ray Imaging and Spectroscopy Mission (XRISM), which was successfully launched on September 7, 2023 (JST). During ground cooling tests of the CCDs in 2020/2021, using the flight-model detector housing, electronic boards, and a mechanical cooler, we encountered an unexpected issue. Anomalous charges appeared outside the imaging area of the CCDs and intruded into the imaging area, causing pulse heights to stick to the maximum value over a wide region. Although this issue has not occurred in subsequent tests or in orbit so far, it could seriously affect the imaging and spectroscopic performance of the SXI if it were to happen in the future. Through experiments with non-flight-model detector components, we successfully reproduced the issue and identified that the anomalous charges intrude via the potential structure created by the charge injection electrode at the top of the imaging area. To prevent anomalous charge intrusion and maintain spectroscopic performance that satisfies the requirements, even if this issue occurs in orbit, we developed a new CCD driving technique. This technique is different from the normal operation in terms of potential structure and its changes during imaging and charge injection. In this paper, we report an overview of the anomalous charge issue, the related potential structures, the development of the new CCD driving technique to prevent the issue, the imaging and spectroscopic performance of the new technique, and the results of investigation experiments to identify the source of the anomalous charges.
Chronos is a X-ray observatory concept capable of “hour-level” follow up observations of transient alerts in 2030s’ multi-messenger astronomy, with 0.3–40+ keV wide X-ray band-width and 250–300 nm ultra-violet (UV) coverage. The mission has a good hard X-ray imaging spectroscopy with > 9′ field of view, the soft X-ray imager with > 30′ field of view, and the UV imager with > 7° field of view. Aiming at launch in mid-2030s, the mission is designed to provide wide-band spectroscopy of time dependent high-energy phenomena. The low background and large effective area in the hard X-ray band also make it good at observing diffuse hard X-ray emissions, such as many TeV sources which will be newly found in 2030s.
XRISM (X-Ray Imaging and Spectroscopy Mission) is an astronomical satellite with the capability of highresolution spectroscopy with the X-ray microcalorimeter, Resolve, and wide field-of-view imaging with the CCD camera, Xtend. The Xtend consists of the mirror assembly (XMA: X-ray Mirror Assembly) and detector (SXI: Soft X-ray Imager). The components of SXI include CCDs, analog and digital electronics, and a mechanical cooler. After the successful launch on September 6th, 2023 (UT) and subsequent critical operations, the mission instruments were turned on and set up. The CCDs have been kept at the designed operating temperature of −110°C after the electronics and cooling system were successfully set up. During the initial operation phase, which continued for more than a month after the critical operations, we verified the observation procedure, stability of the cooling system, all the observation options with different imaging areas and/or timing resolutions, and operations for protection against South Atlantic Anomaly. We optimized the operation procedure and observation parameters including the cooler settings, imaging areas for the specific modes with higher timing resolutions, and event selection algorithm. We summarize our policy and procedure of the initial operations for SXI. We also report on a couple of issues we faced during the initial operations and lessons learned from them.
XRISM (X-ray Imaging and Spectroscopy Mission) is an X-ray astronomy satellite developed in collaboration with JAXA, NASA and ESA. It successfully launched on Sept. 7, 2023. Two complementary X-ray telescopes, Resolve and Xtend are on-board XRISM. Resolve uses the pixelized X-ray micro calorimeter developed by NASA/GSFC and has very high energy resolution of 5 eV. On the other hand, Xtend uses an X-ray CCD camera as its focal plane detector which has high spatial resolution and a wide field of view. We evaluated the performance of the X-ray Mirror Assembly (XMA) for Xtend using data observed during the commissioning and PV phases of XRISM. To verify the imaging performance, the Point Spread Functions (PSF) generated from the observations of NGC 4151 and PDS 456 were compared with the ground-calibration results. The results show that the imaging performance of Xtend-XMA is not significantly different from that of the ground calibration, and that it meet the requirement. The effective area was verified by comparing the results of simultaneous observations of 3C 273 by XRISM and four X-ray astronomy satellites (Chandra, XMM-Newton, NuSTAR, and Swift). The results of the fitting of the X-ray spectrum of Xtend show no significant difference from the results of other satellites, suggesting the effective area used for fitting is correct. The on-axis position on the detector was estimated from the intensity of the Abell 2029 observations at four off-axis angles. The on-axis is about 40 arcsec away from the aim point, and the decrease in effective area at the aim point is less than 1%. Stray light observations of the Crab Nebula at 60 arcmin off-axis were obtained at two different satellite roll angles. The stray light intensity obtained at each roll angle was significantly different, verifying the dependence of the stray light on the roll angle.
We have been developing ultra-lightweight Wolter type-I X-ray telescopes fabricated with MEMS technologies for GEO-X (GEOspace X-ray imager) which is a small satellite mission to perform soft X-ray imaging spectroscopy of the entire Earth’s magnetosphere. The telescope is our original type of micropore optics and possesses lightness (∼5 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 first processed by deep reactive ion etching, which has numerous curvilinear micropores (a 20-μm width) whose sidewalls are utilized as X-ray reflective mirrors. High-temperature hydrogen annealing and chemical mechanical polishing processes are 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 a plasma atomic layer deposition process to focus X-rays with high reflectivity. Finally, we assemble two optics bent with different curvatures (1000- and 333-mm radii) and complete the Wolter type-I telescope. We optimized each process and conducted an X-ray irradiation test to assemble the full-processed optics into an EM telescope for the GEO-X mission, which enabled to complete the telescope to achieve an angular resolution of ∼4.8 arcmin in FWHM in the assembled telescope. We report on our latest development status and the X-ray imaging performance of the GEO-X EM telescope.
The number of magnetospheric solar wind charge exchange (SWCX) soft X-ray events detectable with GEO-X was estimated using the latest calibrated ACE/SWICS data on solar wind O7+ ions. The OVII line flux at a certain solar wind O7+ flux was calculated from an magnetohydrodynamic simulation of 2001 March 31 geomagnetic storm and scaled to the sum of emission lines from other solar wind ions based on Suzaku magnetospheric SWCX events. The instrumental background including radiation noise mainly due to energetic protons was estimated using GOES >10 MeV proton flux and our previously developed GEANT4 simulation. The number of detectable magnetospheric SWCX events that meet a criterion of signal-to-noise ratios grater than 20 peaks near solar maximum, reaching 49.7 events per year with an average duration of 2.94 hours. Assuming an observation efficiency of 30%, we found that at least one event can be detected within a 4-month time frame with a 90% probability.
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 propose an x-ray imaging system, multi-image x-ray interferometer module (MIXIM), with which a very high angular resolution can be achieved even with a small system size. MIXIM is composed of equally spaced multiple slits and an x-ray detector, and its angular resolution is inversely proportional to the distance between them. Here, we report our evaluation experiments of MIXIM with a newly adopted CMOS sensor with a high spatial resolution of 2.5 μm. Our previous experiments with a prototype MIXIM were limited to one-dimensional imaging, and more importantly, the achieved angular resolution was only ∼1 ″ , severely constrained due to the spatial resolution of the adopted sensor with a pixel size of 4.25 μm. By contrast, one-dimensional images obtained in this experiment had a higher angular resolution of 0.5″ when a configured system size was only ∼1 m, which demonstrates that MIXIM can simultaneously realize a high angular resolution and compact size. We also successfully obtained a two-dimensional profile of an x-ray beam for the first time for MIXIM by introducing a periodic pinhole mask. The highest angular resolution achieved in our experiments is smaller than 0.1″ with a mask-sensor distance of 866.5 cm, which shows the high scalability of MIXIM.
In this multi-messenger astronomy era, all the observational probes are improving their sensitivities and overall performance. The Focusing on Relativistic universe and Cosmic Evolution (FORCE) mission, the product of a JAXA/NASA collaboration, will reach a 10 times higher sensitivity in the hard X-ray band (E > 10 keV) in comparison with any previous hard x-ray missions, and provide simultaneous soft x-ray coverage. FORCE aims to be launched in the early 2030s, providing a perfect hard x-ray complement to the ESA flagship mission Athena. FORCE will be the most powerful x-ray probe for discovering obscured/hidden black holes and studying high energy particle acceleration in our Universe and will address how relativistic processes in the universe are realized and how these affect cosmic evolution. FORCE, which will operate over 1–79 keV, is equipped with two identical pairs of supermirrors and wideband x-ray imagers. The mirror and imager are connected by a high mechanical stiffness extensible optical bench with alignment monitor systems with a focal length of 12 m. A light-weight silicon mirror with multi-layer coating realizes a high angular resolution of < 15′′ in half-power diameter in the broad bandpass. The imager is a hybrid of a brand-new SOI-CMOS silicon-pixel detector and a CdTe detector responsible for the softer and harder energy bands, respectively. FORCE will play an essential role in the multi-messenger astronomy in the 2030s with its broadband x-ray sensitivity.
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.
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.
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 (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.
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.
We developed an X-ray imaging spectrometer with a high timing resolution. CMOS image sensors, widely used in optical imaging, have an excellent time resolution with considerably low readout noise. We performed experiments using a Zyla CMOS image sensor manufactured by Andor Technology pic. (UK). It employs a front illuminated(FI) scientific CMOS (sCMOS) with each pixel size of 6.5×6.5μm2. We found that nearly all X-ray events spread more than 5×5 pixels and obtained good energy resolution of 260 eV at 5.9 keV at room temperature. The spectrum shows no degradation at lower energy, which imply that there is negligibly small charge loss. We report photon counting performance for a broad range of X-rays from 3-25keV at room temperature.
We intoduce our novel method of super high resolution astronomical X-ray imaging, Multi Image X-ray Interferometer Method, Modules, Missions (MIXIM). In series of experiments on the ground we not only verified the concept of MIXIM but also realized 2D imaging with angular resolution better than 0. ′′1. Employment of small pixel size CMOS sensor was the key to this achievement. Scalability is also an important feature of MIXIM., and various mission format is available. We show some examples from a very small satellite for sub arcsecond resolution to a formation flight with a millions km separation to gain µas resolution. MIXIM is different from X-ray mirrors in various points, for example, it does not have a collecting power. Considering the limitations and advantages of MIXIM, we should choose bright apparently point-like sources as targets. Nearby AGNs are primary ones, and the MIXIM scope just corresponds to spatial scales which have not yet resolved in X-rays.
X-Ray Imaging and Spectroscopy Mission (XRISM) is the seventh Japanese X-ray astronomical satellite scheduled to be launched in the Japanese fiscal year 2022. XRISM has two mission instruments, “Resolve”, a soft X-ray spectrometer, and “Xtend”, a soft X-ray imager. The Former is an X-ray micro-calorimeter that has ∼ 5 eV of energy resolution with 3′ × 3 ′ of field of view. The Latter is an X-ray CCD camera with 38′ × 38′ of field of view. Both instruments are placed on the focal plane of X-ray telescopes, X-ray Mirror Assembly (XMA). Xtend CCDs are designed almost the same as those of Hitomi (ASTRO-H), whereas some improvements have been applied. In 2019, flight-model (FM) candidates of Xtend CCDs were fabricated by Hamamatsu Photonics K.K. We performed screening experiments to examine whether they met requirements or not, and then selected the best four chips as the FM. We then performed on-ground calibration on August 2019 and September 2019 for the FM chips to determine the gain correction parameters and to construct the detector response with several energies of monochromatic X-ray. In this paper, we report screening, selection, and on-ground calibration processes, especially focusing on the response verification.
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 have proposed a new style X-ray interferometer, Multi-Image X-ray Interferometer Module (MIXIM), to achieve high angular resolution. MIXIM is comprised of a grating and an X-ray detector, and its angular resolution is in inverse proportion to the distance between two components. Although we have already detected a 1D interference fringe which corresponds an angular resolution of about 1” in our past experiment, its amplitude is not so high partly because of the lack of the spatial resolution of the X-ray detector. Then we newly adopt a CMOS detector which has both high spatial resolution (< 2.5 μm) and high spectroscopic capability (FWHM∼ 170 eV @5.9 keV) and evaluate the performance of MIXIM at BL20B2 in SPring-8, the synchrotron radiation facility in Japan. 1D interference fringes in this experiment have much higher amplitudes than those in the past experiment, which demonstrates the improvement of the performance due to the new CMOS detector. We also introduce a 2D grating for the first time, and try to obtain the 2D profile of the X-ray beam of which the size is 0.28” (H) and 0.06” (V). Extending the distance between two components to 866.5 cm, 2D imaging by MIXIM succeeds in capturing the horizontally elongated beam structure. The angular resolution at this configuration is calculated to be 0.076”, which is the highest ever achieved for astronomical X-ray imagers.
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 report current status of developing Soft X-ray Imager (SXI), the X-ray CCD camera onboard X-Ray Imaging and Spectroscopy Mission (XRISM). Four flight model (FM) CCDs have been selected considering several items including energy resolution at 5.9keV, CTI, dark current, etc. We have also completed calibration campaign for all the FM CCDs. Initial analyses show that the response function for monochromatic X-rays is basically the same as that of Hitomi CCDs. The focal plane including the single-stage Stirling cooler has been assembled. Production of key parts in SXI sensor body such as contamination blocking filter and onboard calibration source has been finished and they are waiting for assemble. The digitized signals of the CCD are corrected step by step before conversion to X-ray energy. We are preparing calibration database for the correction such as CTI, gain, and line redistribution function.
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
X-ray polarimetry in astronomy has not been exploited well, despite its importance. The recent innovation of instruments is changing this situation. We focus on a complementary metal–oxide–semiconductor (CMOS) pixel detector with small pixel size and employ it as an x-ray photoelectron tracking polarimeter. The CMOS detector we employ is developed by GPixel Inc. and has a pixel size of 2.5 μm × 2.5 μm. Although it is designed for visible light, we succeed in detecting x-ray photons with an energy resolution of 176 eV (FWHM) at 5.9 keV at room temperature and the atmospheric condition. We measure the x-ray detection efficiency and polarimetry sensitivity by irradiating polarized monochromatic x-rays at BL20B2 in SPring-8, the synchrotron radiation facility in Japan. We obtain modulation factors of 7.63 % ± 0.07 % and 15.5 % ± 0.4 % at 12.4 and 24.8 keV, respectively. It demonstrates that this sensor can be used as an x-ray imaging spectrometer and polarimeter with the highest spatial resolution ever tested.
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.
X-ray Imaging Spectrometers (XIS) are the X-ray CCD cameras onboard Suzaku. They were operated in orbit from 2005 to 2015 and produced lots of findings with their good energy resolution and low non X-rat background. Precise calibration including the 10 eV accuracy in the energy scale reinforced them. Nevertheless, there has been a unresolved calibration issue in the spectral response around the Si-K edge (1.839 keV) appearing as systematic residuals up to 10%. The residual is negative peaking at 1.85 keV in the front illuminated (FI) sensors and positive peaking at 1.8 keV in the back illuminated (BI) sensor for X-ray sources dominated by continuum X-ray emission. Various attempts to eliminate these residuals by changing response parameters or quantum efficiency models have been insufficient. In this paper, we revisit this problem by focusing on the relation between incident X-ray energy and pulse height. We introduce a jump in that relation at the Si-K edge by modifying the , and optimize its value so as to minimize the residuals in the fit of the X-ray spectra for the black hole binary LMC X-3, a source dominated by continuum emission. We find the introduction of a jump significantly reduces the residuals. The optimized jump values are +4:2 channel, +4:0 channel, and -3:1 channel, corresponding to 15.3 eV, -11:3 eV, and 14.6 eV, for XIS0, XIS3 (FI), and XIS1 (BI), respectively. The direction of the jump is opposite for the FI and for the BI. We revise the response matrices generator so as to include the jump for each XIS sensor, and apply it to the X-ray spectra of the Perseus cluster of galaxies which has various emission lines in the spectra, and the blazar PKS2155-304 which was observed various epoch in the Suzakuoperation. We confirm the residuals are significantly reduced for these sources, too. We finally suggest the jump at Si-K edge in the energy and pulse height relation is qualitatively explained, if some of charges are lost in course of charger collection to the electrode of the CCD in the depletion later, and its amount is large for larger travel length in the depletion layer. If this explanation is correct, the Si-K edge problem and its solution presented in this paper is not specific only for the SuzakuXIS but also for other X-ray CCDs.
X-ray Astronomy Recovery Mission (XARM) scheduled to be launched in early 2020’s carries two soft X-ray telescopes. One is Resolve consisting of a soft X-ray mirror and a micro calorimeter array, and the other is Soft X-ray Imaging Telescope (Xtend), a combination of an X-ray mirror assembly (XMA) and an X-ray CCD camera (SXI). Xtend covers a field of view (FOV) of 38′ × 38′ , much larger than that of Resolve (3′ × 3 ′ ) with moderate energy resolution in the energy band from 0.4 keV to 13 keV, which is similar to that of Resolve (from 0.3 keV to 12 keV). Simultaneous observations of both telescopes provide complimentary data of X-ray sources in their FOV. In particular, monitoring X-ray sources outside the Resolve FOV but inside the Xtend FOV is important to enhance the reliability of super high resolution spectra obtained with Resolve. Xtend is also expected to be one of the best instruments for low surface brightness X-ray emissions with its low non X-ray background level, which is comparable to that of Suzaku XIS. The design of Xtend is almost identical to those of Soft X-ray Telescope (SXT) and Soft X-ray Imager (SXI) both on board the Hitomi satellite. However, several mandatory updates are included. Updates for the CCD chips are verified with experiment using test CCD chips before finalizing the design of the flight model CCD. Fabrication of the foils for XMA has started, and flight model production of the SXI is almost ready.
We have proposed a new type of X-ray interferometer called Multi Image X-ray Interferometer Module (MIXIM) consisting simply of a grating and an X-ray spectral imaging detector. The baseline concept of MIXIM is a slit camera to obtain the profile of X-ray sources, but aim to get a sub-arcsecond resolution. For that purpose, to avoid blurring of the image by diffraction is a key, and we select X-ray events of which energy satisfies the interferometric condition called Talbot effect. Stacking the images (X-ray interferometric fringes) with the period of the grating is another point of the method, which provides the self image of a grating slit convolved with the profile of the X-ray source. We started an experiment with a micro focus X-ray source, 4.8 μm pitch grating, and an SOI type X-ray detector XRPIX2b with a pixel size of 30 μm. The stacked self image was obtained with a magnification factor of 4.4. We, however, need finer positional resolution for the detector to obtain the self image to a parallel beam, for which the magnification factor must be 1. We thus focused on small pixel size CMOS sensors developed for visible light. We irradiated X-rays to one of such CMOS sensors GSENSE5130 with a pixel size of 4.25 μm, and found enough capability to detect X-rays, i.e., FWHM of 207 eV at 5.9 keV at room temperature. We then employed this sensor and performed an experiment at a 200 m beam line of BL20B2 in the synchrotron facility SPring8. Using a grating with a pitch of 4.8 µm and an opening fraction of f=0.5, we obtained the self image of the grating at the detector distance from the grating of 23 cm and 46 cm and the X-ray energy of 12.4 keV. We also performed an experiment using a 9.6 μm f = 0.2 grating with a detector-grating distance of 92 cm, and obtained higher contrast image of the grating. Note that the slit width of 2.4 μm at 46 cm corresponds to 1.1′′, while that of 1.9 μm at 92 cm does 0.43′′. We suggest several format of possible MIXIM missions, including MIXIM-S for very small satellite of 50cm size, MIXIM-P for parasite use of nominal X-ray observatory employing grazing X-ray telescopes with a focal length of 10 m, and MIXIM-Z in which the grating-detector distance of 100 m is acquired by formation flight or free fryers to yield 0.01” level resolution.
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.
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.
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 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 Imager (SXI) is an imaging spectrometer using charge-coupled devices (CCDs) aboard the Hitomi x-ray observatory. The SXI sensor has four CCDs with an imaging area size of 31 mm×31 mm arranged in a 2×2 array. Combined with the x-ray mirror, the Soft X-ray Telescope, the SXI detects x-rays between 0.4 and 12 keV and covers a 38′×38′ field of view. The CCDs are P-channel fully depleted, back-illumination type with a depletion layer thickness of 200 μm. Low operation temperature down to −120°C as well as charge injection is employed to reduce the charge transfer inefficiency (CTI) of the CCDs. The functionality and performance of the SXI are verified in on-ground tests. The energy resolution measured is 161 to 170 eV in full width at half maximum for 5.9-keV x-rays. In the tests, we found that the CTI of some regions is significantly higher. A method is developed to properly treat the position-dependent CTI. Another problem we found is pinholes in the Al coating on the incident surface of the CCDs for optical light blocking. The Al thickness of the contamination blocking filter is increased to sufficiently block optical light.
A new type of X-ray interferometer consisting of a grating and an X-ray spectral imaging detector is proposed. Parallel X-ray beam irradiating a grating makes the fringes on the X-ray detector. Each fringe represents the profiles of the X-ray source, and superposition of those fringe images makes the accurate source profile, when diffraction is negligible. We estimate the angular resolution of this system with 1m distance between the grating and the detector is limited to about 6.5" for 12.4 keV X-rays in the condition that the diffraction is negligible. However, even when the diffraction is significant, e.g., with a finer pitch grating, interference, or more specifically the Talbot effect, make the clear fringes at a specific distance known as the Talbot distance. If we place the X-ray detector at a distance and select X-ray events meeting the Talbot condition, we expect the fringes that is a self image of the grating, representing the source profile. If we employ, for example, 5 μm pitch grating 25 cm apart from the detector and select 12.4 keV X-rays, the angular resolution of 2" or better is expected. We consider there are significant room to improvement. We also show the experimental setup we have started in our laboratory.
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.
We report here the performance of the SXI on ASTRO-H that was started its operation from March,02 2016. The SXI consists of 4 CCDs that cover 38' X 38' sky region. They are P-channel back-illumination type CCD with a depletion layer of 200 μm. Charge injection (CI) method is applied from its beginning of the mission. Two single stage sterling coolers are equipped with the SXI while one of them has enough power to cool the CCD to -110°C. There are two issues in the SXI performance: one is a light-leak and the other is a cosmic-ray echo. The light-leak is due to the fact that the day-Earth irradiates visible lights onto the SXI body through holes in the satellite base plate. It can be avoided by selecting targets not on the anti-day-Earth direction. The cosmic-ray echo is due to the improper parameter values that is fixed by revising them with which the cosmic-ray echo does not affect the image. Using the results of RXJ1856.5-3754, we confirm that the possible contaminants on the CCD is well within our expectation.
The Soft X-ray Imager (SXI) is an X-ray CCD camera onboard the ASTRO-H X-ray observatory. The CCD chip used is a P-channel back-illuminated type, and has a 200-µm thick depletion layer, with which the SXI covers the energy range between 0.4 keV and 12 keV. Its imaging area has a size of 31 mm x 31 mm. We arrange four of the CCD chips in a 2 by 2 grid so that we can cover a large field-of-view of 38’ x 38’. We cool the CCDs to -120 °C with a single-stage Stirling cooler. As was done for the CCD camera of the Suzaku satellite, XIS, artificial charges are injected to selected rows in order to recover charge transfer inefficiency due to radiation damage caused by in-orbit cosmic rays. We completed fabrication of flight models of the SXI and installed them into the satellite. We verified the performance of the SXI in a series of satellite tests. On-ground calibrations were also carried out and detailed studies are ongoing.
Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched in 2015. The SXI camera contains four CCD chips, each with an imaging area of 31mm x 31 mm, arrayed in mosaic, covering the whole FOV area of 38′ x 38′. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200 _m. High QE of 77% at 10 keV expected for this device is an advantage to cover an overlapping energy band with the Hard X-ray Imager (HXI) onboard ASTRO-H. Most of the flight components of the SXI system are completed until the end of 2013 and assembled, and an end-to-end test is performed. Basic performance is verified to meet the requirements. Similar performance is confirmed in the first integration test of the satellite performed in March to June 2014, in which the energy resolution at 5.9 keV of 160 eV is obtained. In parallel to these activities, calibrations using engineering model CCDs are performed, including QE, transmission of a filter, linearity, and response profiles.
A formation flight astronomical survey telescope (FFAST) is a new project that will cover a large sky area in hard X-ray. In particular, it will focus on the energy range up to 80keV. It consists of two small satellites that will go in a formation flight. One is an X-ray telescope satellite carrying a super mirror, and the other is a detector satellite carrying an SDCCD. Two satellites are put into a low earth orbit in keeping the separation of 12m. This will survey a large sky area at hard X-ray region to study the evolution of the universe.
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 report on the development status of the readout ASIC for an onboard X-ray CCD camera. The quick low- noise readout is essential for the pile-up free imaging spectroscopy with the future highly sensitive telescope. The dedicated ASIC for ASTRO-H/SXI has sufficient noise performance only at the slow pixel rate of 68 kHz. Then we have been developing the upgraded ASIC with the fourth-order ΔΣ modulators. Upgrading the order of the modulator enables us to oversample the CCD signals less times so that we. The digitized pulse height is a serial bit stream that is decrypted with a decimation filter. The weighting coefficient of the filter is optimized to maximize the signal-to-noise ratio by a simulation. We present the performances such as the input equivalent noise (IEN), gain, effective signal range. The digitized pulse height data are successfully obtained in the first functional test up to 625 kHz. IEN is almost the same as that obtained with the chip for ASTRO-H/SXI. The residuals from the gain function is about 0.1%, which is better than that of the conventional ASIC by a factor of two. Assuming that the gain of the CCD is the same as that for ASTRO-H, the effective range is 30 keV in the case of the maximum gain. By changing the gain it can manage the signal charges of 100 ke-. These results will be fed back to the optimization of the pulse height decrypting filter.
FFAST is a large area sky survey mission at hard X-ray region by using a spacecraft formation flying. It consists of two small satellites, a telescope satellite, carrying a multilayer super mirror, and a detector satellite, carrying scintillator-deposited CCDs (SD-CCDs). SD-CCD is the imaging device which realized sensitivity to 80 keV by pasting up a scintillator on CCD directly. Soft X-ray events are directly detected in the CCD. On the other hand, Hard X-ray events are converted to optical photons by the scintillator and then the CCD detects the photons. We have obtained the spectrum with 109Cd and successfully detected the events originated from the CsI.
For a space use of a CCD, we have to understand aged deterioration of CCD in high radiative environments. In addition, in the case of SD-CCD, we must investigate the influence of radio-activation of a scintillator. We performed experiments of proton irradiation to the SD-CCD as space environmental tests of cosmic rays.
The SD-CCD is irradiated with the protons with the energy of 100 MeV and neglected for about 150 hours. As a result, the derived CTI profile of SD-CCD is similarly to ones of XIS/Suzaku and NeXT4 CCD/ASTRO-H. In contrast, CTIs derived from the data within 4 hours after irradiation is 10 times or more larger than the ones after 150 hours. This may be due to influence of an annealing. We also report a performance study of SD-CCD, including the detection of scintillation events, before proton irradiation.
The Soft X-ray Imager, SXI, is an X-ray CCD camera onboard the ASTRO-H satellite to be launched in 2015. ASTRO-H will carry two types of soft X-ray detector. The X-ray calorimeter, SXS, has an excellent energy resolution with a narrow field of view while the SXI has a medium energy resolution with a large field of view, 38′ square. We employ 4 CCDs of P-channel type with a depletion layer of 200 μm. Having passed the CDR, we assemble the FM so that we can join the final assembly. We present here the SXI status and its expected performance in orbit.
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.
Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched
in 2014. The SXI camera contains four CCD chips, each with an imaging area of 31mm×
31 mm, arrayed in
mosaic, which cover the whole FOV area of 38' ×
38'. The SXI CCDs are a P-channel back-illuminated (BI) type
with a depletion layer thickness of 200 μm. High QE of 77% at 10 keV expected for this device is an advantage
to cover an overlapping energy band with the Hard X-ray Imager (HXI) onboard ASTRO-H. Verification with
engineering model of the SXI has been performed since 2011. Flight model design was fixed and its fabrication
has started in 2012.
We report on the development of the X-ray CCD for the soft X-ray imager (SXI) onboard ASTRO-H. SXI CCDs are
P-channel, back-illuminated type manufactured by Hamamatsu Photonics K. K.
Experiments with prototype CCD for the SXI shows the device has a depletion layer as thick as 200μm, high efficiency for hard X-rays.
By irradiating soft X-rays to the prototype CCD for the SXI.
At the same time, we found a significant low energy tail in the soft X-ray response of the SXI prototype CCD.
We thus made several small size CCD chips with different treatment in processing the surface layers.
CCDs with one of the surface layers treatment show a low energy tail of
which intensity is one order of magnitude smaller than that of the original SXI prototype CCD for 0.5keV X-ray incidence.
The same treatment will be applied to the flight model CCDs of the SXI.
We also performed experiments to inject charge with the SXI prototype CCD, which is needed to mitigate the radiation damage in the orbit.
We investigated the operation conditions of the charge injection.
Using the potential equilibration method, charges are injected in each column homogeneously,
though the amount of the charge must be larger than 20ke-.
Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched
in 2014. The SXI camera contains four CCD chips, each with an imaing aread of 31mmx31 mm, arrayed in
mosaic, which cover the whole FOV area of 38'x38'. The SXI CCD of which model name is HPK Pch-NeXT4
is a P-channel type, back-illuminated, fully depleted device with a thickness of 200μm. We have developed an
engineering model of the SXI camera body with coolers, and analog electronics for them. Combined with the
bread board digital electronics, we succeeded in operation the whole the SXI system. The CCDs are cooled down
to -120°C with this system, and X-rays from 55Fe sources are detected. Although optimization of the system is in
progress, the energy resolution of typical 200 eV and best 156 eV (FWHM) at 5.9 keV are obtained. The readout
noise is 10 e- to 15 e-, and to be improved its goal value of 5 e-. On-going function tests and environment tests
reveal some issues to be solved until the producntion of the SXI flight model in 2012.
We present the development of the data acquisition system for the X-ray CCD camera (SXI: Soft X-ray Imager)
onboard the ASTRO-H satellite. Two types of breadboard models (BBMs) of SXI electronics have been produced
to verify the functions of each circuit board and to establish the data acquisition system from CCD to SpaceWire
(SpW) I/F. Using BBM0, we verified the basic design of the CCD driver, function of the Δ∑-ADC, data
acquisition of the frame image, and stability of the SpW communication. We could demonstrate the energy
resolution of 164 eV (FWHM) at 5.9 keV. Using BBM1, we verified acquisition of the housekeeping information
and the frame images.
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.
We are designing an X-ray CCD camera (SXI) for ASTRO-H, including many new items. We have developed
the CCD, CCD-NeXT4, that is a P-channel type CCD. It has a thick depletion layer of 200μm with an imaging
area of 30mm square. Since it is back-illuminated, it has a good low energy response and is robust against the
impact of micro-meteorites. We will employ 4 chips to cover the area of 60mm square. A mechanical rather
than peltier cooler will be employed so that we can cool the CCD to -120°C. We will also introduce an analog
ASIC that is placed very close to the CCD. It performs well, having a similar noise level to that assembled by
using individual parts used on SUZAKU. We also employ a modulated X-ray source (MXS), that improves the
accuracy of the calibration. The SXI will have one of the largest SΩ among various satellites.
We have developed a new back-illuminated (BI) CCD which has an Optical Blocking Layer (OBL) directly coating
its X-ray illumination surface with Aluminum-Polyimide-Aluminum instead of Optical Blocking Filter (OBF).
OBL is composed of a thin polyimide layer sandwiched by two Al layers. Polyimide and Al has a capability to
cut EUV and optical light, respectively. The X-ray CCD is affected by large doses of extreme ultraviolet (EUV)
radiation from Earth sun-lit atmosphere (airglow) in orbit as well as the optical light.
In order to evaluate the performance of the EUV-attenuating polyimide of the OBL, we measured the EUV
transmission of both the OBL and the OBF at energies between 15-72 eV by utilizing a beam line located
at the Photon Factory in High Energy Accelerator Research Organization (KEK-PF). We obtained the EUV
transmission to be 3% at 41 eV which is the same as the expected transmission from the designed thickness of
the polyimide layer. We also found no significant change of the EUV transmission of polyimide over the nine
month interval spanned by out two experiments.
We also measured the optical transmission of the OBL at wavelengths between 500-900Å to evaluate the
performance of the Al that attenuates optical light, and found the optical transmission to be less than 4×10-5.
We report on the performance of an analog application-specified integrated circuit (ASIC) developed for the front-end electronics of the X-ray CCD camera system (SXI: Soft X-ray Imager) onboard the ASTRO-H satellite. The ASIC consists of four identical channels and they simultaneously process the CCD signals at the pixel rate of 68kHz. Delta-Sigma modulator is adopted to achieve effective noise shaping and obtain a high resolution decimal values with relatively simple circuits. We will implement 16 ASIC chips in total in the focal plane assembly. The results of the unit test shows that it works properly with moderately low input noise of <30μV at the pixel rate of 80kHz. Power consumption is sufficiently low of 150mW. Dynamic range of input signals is +-20mV that covers effective energy range of the CCD chips of SXI (0.2-20keV). The integrated non-linearity of 0.2% satisfies the same performance as the conventional CCD detectors in orbit. The radiation tolerance against total ionizing dose (TID) effect and single event latch-up (SEL) has also been investigated. The irradiation test using 60Co gamma-rays and proton beam showed that the ASIC has sufficient tolerance against TID up to 200 and 167krad respectively, which thoroughly exceeds the expected operating duration in the planned low-inclination low-earth orbit. The irradiation of the Fe ion beam also showed no latch-up nor malfunctions up to the fluence of 4.7x10^7ions. The threshold against SEL is larger than 1.68MeVcm^2/mg, which is sufficiently high enough that SEL events should not be a major cause of instrument downtime.
We have developed application specific integrated
circuits(ASICs) for multi-readout X-ray CCDs in order to improve their
time resolution. ASICs with the size of 3mm × 3mm were fabricated by employing a Taiwan
Semiconductor Manufacturing Company(TSMC) 0.35 μm CMOS technology.
The number of channels is 4 and the each channel consists of a
preamplifier, 5-bit DAC and delta-sigma analog-to-digital converters
(ADCs). The measured equivalent input noise at the
pixel rate of 19.5 kHz and 625 kHz are 36 μV and 51 μV,
respectively. The power consumption is about 110 mW/chip at 625 kHz pixel rate,
which is about 10 times lower than that of our existing system.
We now expect to employ an ASIC as the readout system of X-ray CCD camera onboard the next Japanese X-ray astronomy satellite. We tested the
readout of the prototype X-ray CCDs by using ASICs and the total-dose effects of ASICs. We describe the overview of our ASICs and test results.
The X-ray Imaging Spectrometer (XIS) on board the Suzaku satellite is an X-ray CCD camera system that has features of a low background, high quantum efficiency, and good energy resolution in the 0.2 - 12 keV band. Because of the radiation damage, however, the energy resolution of the XIS has been degraded since Suzaku was launched (July 2005).
One of the major advantages of the XIS over the other X-ray CCDs in orbit is the provision of a precision charge injection (CI) capability. In order to improve the energy resolution, the precise measurement of charge transfer inefficiency (CTI) is essential. For this purpose, we applied the checker-flag CI, and we were able to measure the CTI of each CCD column. Furthermore, we were able to obtain the pulse height dependency of the CTI.
Our precise CTI correction using these results improved the energy resolution from 193 eV to 173 eV in FWHM at 5.9 keV in July 2006 (one year after the launch).
The energy resolution can be improved also by reducing the CTI. For this purpose, we applied the spaced-row charge injection (SCI); periodically injected artificial charges
work as if they compensate radiation-induced traps and prevent electrons produced by X-rays from being captured by the charge traps. Using this method, the energy resolution improved from 210 eV to 150 eV at 5.9 keV in September 2006, which is close to the resolution just after the launch (145 eV).
We report the current in-orbit calibration status of the XIS data using these two techniques. We present the time history of the gain and energy resolution determined from onboard calibration sources (55Fe) and observed calibration objects like E0102-72.
We report on the development of high-speed and low-noise readout system of X-ray CCD camera with ASIC and the Camera Link standard.
The ASIC is characterized by AD-conversion capability and it processes CCD output signals with a high pixel rate of 600 kHz, which is ten times quicker than conventional frame transfer type X-ray CCD cameras in orbit.
There are four identical circuits inside the chip and all of them process CCD signals simultaneously. ΔΣ modulator is adopted to achieve effective noise shaping and obtain a high resolution decimal values with relatively simple circuits.
The results of the unit test shows that it works properly with moderately low input noise of ~70 μV at pixel rate of 625 kHz, and ~40 μV @ 40 kHz.
Power consumption is sufficiently low of <120 μuV @ 1.25 MHz. We have also developed the rest of readout and driving circuits. As a data acquisition scheme we adopt the Camera Link standard in order to support the high readout rate of the ASIC.
In the initial test of the CCD camera system, we used the P-channel CCD developed for Soft X-ray Imager onboard next Japanese X-ray astronomical satellite. The thickness of its depletion layer reaches up to 220 μm and therefore we can detect the X-rays from 109Cd with high sensitivity rather than N-channel CCDs. The energy resolution by our system is 379 (±7)eV (FWHM) @ 22.1 keV, that is, ΔE/E=1.8% was achieved with a readout rate of 44 kHz.
The Soft X-ray Imager (SXI) is the X-ray CCD detector system on board the NeXT mission that is to be launched around 2013. The system consists of a camera, an SXI-specific data processing unit (SXI-E) and a CPU unit commonly used throughout the NeXT satellite. All the analog signal handling is restricted within the camera unit, and all the I/O of the unit are digital.
The camera unit and SXI-E are connected by multiple LVDS lines, and SXI-E and the CPU unit will be connected by a SpaceWire (SpW) network. The network can connect SXI-E to multiple CPU units (the formal SXI CPU and neighbors) and all the CPU units in the network have connections to multiple neighbors: with this configuration, the SXI system can work even in the case that one SpW connection or the formal SXI CPU is down.
The main tasks of SXI-E are to generate the CCD driving pattern, the acquisition of the image data stream and HK data supplied by the camera and transfer them to the CPU unit with the Remote Memory Access Protocol (RMAP) over SpW. In addition to them, SXI-E also detects the pixels whose values are higher than the event threshold and both adjacent pixels in the same line, and send their coordinates to the CPU unit. The CPU unit can reduce its load significantly with this information because it gets rid of the necessity to scan whole the image to detect X-ray events.
The CCD detectors in the X-ray Imaging Spectrometers (XIS) aboard Suzaku have been equipped with a precision
charge injection capability. The purposes of this capability are to measure and reduce the detector degradation
caused by charged particle radiation encountered on-orbit. Here we report the first results from routine operation
of the XIS charge injection function. After 12 months' exposure of the XIS to the on-orbit charged particle
environment, charge injection already provided measurable improvements in detector performance: the observed
width of the 5.9 keV line from the onboard calibration source was reduced from 205 eV to less than 145 eV.
The rate of degradation is also significantly smaller with charge injection, so its benefit will increase as the
mission progresses. Measured at 5.9 keV, the radiation-induced rate of gain degradation is reduced by a factor
of 4.3 ± 0.1 in the front-illuminated sensors when injecting charge greater than 6 keV equivalent per pixel. The
corresponding rate of degradation in spectral resolution is reduced by a factor 6.5 ± 0.3. Injection of a smaller
quantity of injected charge in the back-illuminated XIS sensor produces commensurately smaller improvement
factors. Excellent uniformity of the injected charge pattern is essential to the effectiveness of charge injection in
the XIS.
The energy resolution of the X-ray CCDs onboard the Suzaku satellite (X-ray Imaging Spectrometer; XIS) has
been degraded since the launch due to radiation damage. To recover from this, we have applied a spaced-row
charge injection (SCI) technique to the Suzaku XIS in orbit. By injecting charge into CCD rows periodically,
the energy resolution 14 months after launch is improved from 210 eV to 150 eV at 5.9 keV, which is close to
the resolution just after the launch (140 eV). Additional information on these results is given in a companion
paper by the XIS team. In this paper, we report the details of CCD charge transfer inefficiency (CTI) in the
SCI mode, the correction method, and the implementation of it in ground analysis software for XIS data. In the
SCI mode, CTI depends on the distance of a charge packet from the nearest charge-injected row, and the gain
shows a periodic non-uniformity. Using flight data obtained with the onboard calibration sources, as well as a
cosmic source (the Perseus cluster of galaxies), we studied the non-uniformity in detail. We developed a method
to correct for the non-uniformity that will be valuable as the radiation damage progresses in future.
We summarize the on-orbit performance of the CCD detectors in the Suzaku X-ray Imaging Spectrometer during the first eight months of the mission. Gradual changes in energy scale, spectral resolution and other performance characteristics, mainly due to radiation exposure, are presented and compared with pre-launch expectations.
The X-ray Imaging Spectrometer on the Suzaku satellite consists three front-illuminated (FI) and one back-illuminated (BI) CCD cameras. Using ground calibration data taken at Kyoto University and Osaka University, we obtained the energy response of the XIS, which consists of at least six components: 1. a main peak, 2. a sub peak, 3. a triangle component, 4. a Si escape, 5. a Si line, and 6. a constant component. The relation between the energy and the pulse height was also estimated, which is called as a gain. The relation cannot be represented with a single linear function. Then we divided the gain into two parts at the Si edge (1.839 keV) and each part can be described with a single linear function. Thus there is a discontinuity at 1.839 keV in the XIS gain. We have monitored the variation of the gain and energy resolution in orbit by observing the calibration source of 55Fe illuminating two corners of each CCD.
Suzaku is the fifth Japanese X-ray astronomical satellite and it was launched in July 2005. The Suzaku X-ray
Imaging Spectrometers (XISs) consist of four X-ray Charge-Coupled Device (CCD) cameras. Three of them are
front-illuminated (FI) CCD, and the other is back-illuminated (BI) CCD. The strong points of the XIS are a
high energy resolution, a large effective area, and a low and stable background. In particular, the background
level of the Suzaku/XIS is much lower than the other X-ray satellites, XMM-Newton/EPIC and Chandra/ACIS.
We investigated the background property of the XIS using the data obtained when the satellite is looking at the
night earth, and proved the low level and the stability of the XIS background. Non X-ray background (NXB)
consists of continuum component and some emission lines. The continuum component is very different between
the FI-CCD and the BI-CCD. We discussed the positional dependence of the continuum component and the line
components, and proved that the flux of the line components of the NXB is higher in the frame-store region than
the imaging area. Finally, we investigated the effects of magnetic cut-off rigidity (COR) upon the count rate of
NXB.
We report on the results of the ground calibration of Astro-E2/XIS with front-illuminated (FI) chips. The sensors have basically the same performance as that of Astro-E/XIS. However, there are some improved points: (1) A 55Fe radio isotope is equipped on a door, and (2) a charge injection (CI)capability (described below) is added. The FI sensors have been calibrated at Kyoto University, Osaka University, and MIT. At Kyoto University we focus on the high energy range (>1.5 keV). We measured the gain, energy resolution, and quantum efficiency as the function of energy by using characteristic X-rays for each sensor. An energy resolution of 130 eV@5.9 keV (FWHM) and a quantum efficiency of 82%@6.4 keV are achieved. After XIS is launched, the Charge Transfer Inefficiency (CTI) increases due to the radiation damage by cosmic rays. Then XIS equips the CI capability to calibrate and compensate the increase of the CTI. In order to utilize the CI capability, the amount of charge injected into the CCDs is expected to be kept constant. The time variability of the amount of the injected charge is estimated.
Diesel engines are useful for commercial vehicles because of low fuel consumption and CO2 emissions that cause the greenhouse effect. However, it is necessary for environmental conservation to develop clean combustion. For thirty years, the combustion phenomena of diesel engines using combustion chamber visualization techniques have been widely studied by many researchers. Since in-cylinder flame temperature affects directly on NOx characteristics in engines, this phenomena has been studied in detail in multi-cylinder diesel engines using a new method to measure the in-cylinder temperature distribution by a two color method. Typical two color methods for two dimensional temperature distribution have used negative color films as recording media. So it took several days to analyze the flame temperature. However since the new system consists of a CCD camera and computer, the analyzing time is reduced to about 10 minutes. Parametric studies on injection timings, engine loads, intake valve layouts, and EGR rates using multi-cylinder commercial engines were carried out to investigate the effect of the flame temperature on NOx concentration. Each parameter study showed that the maximum temperature which occurred in a local stoichiometric combustion area of flame is correlative with NOx emissions rather than mean temperature.
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