We have been developing an X-ray imaging system, multi-image X-ray interferometer module (MIXIM), to achieve a high angular resolution with a compact system size. MIXIM is comprised of a mask with equally spaced apertures and an X-ray detector. The aperture size and the mask-detector distance determine the system’s angular resolution. Although a smaller aperture gives a better resolution, the degree of improvement is limited by a diffraction effect. MIXIM circumvents this problem by utilizing the Talbot effect. Our experiment with the previous model equipped with a multi-pinhole mask obtained an angular resolution of 0.5″ with a mask-detector distance of 92 cm. A major downside of the multi-pinhole mask is, however, that it has a very low opening fraction, which results in a very low effective area. Here, we newly adopt a multiple coded aperture (MCA) mask, an array of coded aperture patterns. Our proof-of-concept experiment demonstrates that the Talbot effect works even for the MCA mask with a high opening fraction of ∼50% at 12.4 keV. Consequently, the new MIXIM realizes ∼25 times as large an effective area as that of the previous model while maintaining a high angular resolution of 0.2″ and a compact size of ∼1.5 m.
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.
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.
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.
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.
IXPE, the first observatory dedicated to imaging x-ray polarimetry, was launched on Dec 9, 2021 and is operating successfully. A partnership between NASA and the Italian Space Agencey (ASI) IXPE features three x-ray telescopes each comprised of a mirror module assembly with a polarization sensitive detector at its focus. An extending boom was deployed on orbit to provide the necessary 4 m focal length. A three-axis-stabilized spacecraft provides power, attitude determination and control, and commanding. After one year of observation IXPE has measured statistically significant polarization from almost all the classes of celestial sources that emit X-rays. In the following we describe the IXPE mission, reporting on its performance after 1.5 year of operations. We show the main astrophysical results which are outstanding for a SMEX mission.
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.
XL-Calibur is a balloon-borne mission for hard x-ray polarimetry. The first launch is currently scheduled from Sweden in summer 2022. Japanese collaborators provide a hard x-ray telescope to the mission. The telescope’s design is identical to the Hard X-ray Telescope (HXT, conically-approximated Wolter-I optics) on board ASTROH with the same focal length of 12 m and the aperture of 45 cm, which can focus x-rays up to 80 keV. The telescope is divided into three segments in the circumferential direction, and confocal 213 grazing-incidence mirrors are precisely placed in the primary and secondary sections of each segment. The surfaces of the mirrors are coated with Pt/C depth-graded multilayer to reflect hard x-rays efficiently by the Bragg reflection. To achieve the best focus, optical adjustment of all of the segments was performed at the SPring-8/BL20B2 synchrotron radiation facility during 2020. A final performance evaluation was conducted in June 2021 and the experiment yields the effective area of 175 cm2 and 73 cm2 at 30 keV and 50 keV, respectively, with its half-power diameter of the point spread function as 2.1 arcmin. The field of view, defined as the full width of the half-maximum of the vignetting curve, is 5.9 arcmin.
We have developed a novel x-ray interferometer, multi-image x-ray interferometer module (MIXIM), comprised of a fine aperture mask and an x-ray detector. The angular resolution of this system can be improved with an increase of the distance between two components or a decrease of the aperture size. Although MIXIM has already achieved an angular resolution of less than 0.1” by applying the Talbot effect with a periodic multi-pinhole mask, there remains the issue that its low opening fraction of 1.3% decreases the effective area of the imaging system. Therefore, we newly introduced periodic coded aperture masks which have opening fractions of about 50% instead of the multi-pinhole mask. Conducting an experiment with a 12.4 keV parallel x-ray beam, we successfully demonstrated that the periodic coded aperture could form the self-image, and obtained the x-ray source profile with sub-arcsecond angular resolution by deciphering the coded pattern. The effective area increases about 25 times compared with the multi-pinhole mask by the introduction of the periodic coded aperture masks, which indicates that this novel method can be effective for addressing the problem.
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.
This paper introduces a second-generation balloon-borne hard X-ray polarimetry mission, XL-Calibur. X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as pulsars and binary black hole systems. The XL-Calibur contains a grazing incidence X-ray telescope with a focal plane detector unit that is sensitive to linear polarization. The telescope is very similar in design to the ASTRO-H HXT telescopes that has the world’s largest effective area above ~10 keV. The detector unit combines a low atomic number Compton scatterer with a CdZnTe detector assembly to measure the polarization making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. It also contains a CdZnTe imager at the bottom. The detector assembly is surrounded by the improved anti-coincidence shielding, giving a better sensitivity. The pointing system with arcsecond accuracy will be achieved.
XL-Calibur is a balloon-borne hard X-ray polarimetry mission, the first flight of which is currently foreseen for 2021. XL-Calibur carries an X-ray telescope consists of consists of 213 Wolter I grazing-incidence mirrors which are nested in a coaxial and cofocal configuration. The optics design is nearly identical to the Hard X-ray Telescope (HXT) on board the ASTRO-H satellite. The telescope was originally fabricated for the Formation Flying Astronomical Survey Telescope (FFAST) project. However, the telescope can be used for XL-Calibur, since the FFAST project was terminated before completion. The mirror surfaces are coated with Pt/C depth-graded multilayers to reflect hard X-rays above 10 keV by Bragg reflection. The effective area of the telescope is larger than 300 cm^2 at 30 keV. The mirrors are supported by alignment bars in the housing, and each of the bars has a series of 213 grooves to hold the mirrors. To obtain the best focus of the optics, the positions of the mirrors have to be adjusted by tuning the positions of the alignment bars. The tuning of the mirror positions is conducted using the X-ray beam at the synchrotron facility SPring-8 BL20B2, and this process is called optical tuning. First the positions of the second reflectors are tuned, and then those of the first reflectors are tuned. We did the first optical tuning in Jan 2020. The second tuning will be planned between April to July, 2020. This paper reports the current status of the hard X-ray telescope for XL-Calibur.
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.
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.
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.
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 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.
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.
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.
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.
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.
Hard X-ray imaging polarimeters are developed for the X-ray γ-ray polaeimtery satellite PolariS. The imaging polarimter is scattering type, in which anisotropy in the direction of Compton scattering is employed to measure the hard X-ray (10-80 keV) polarization, and is installed on the focal planes of hard X-ray telescopes. We have updated the design of the model so as to cover larger solid angles of scattering direction. We also examine the event selection algorithm to optimize the detection efficiency of recoiled electrons in plastic scintillators. We succeed in improving the efficiency by factor of about 3-4 from the previous algorithm and criteria for 18-30 keV incidence. For 23 keV X-ray incidence, the recoiled electron energy is about 1 keV. We measured the efficiency to detect recoiled electrons in this case, and found about half of the theoretical limit. The improvement in this efficiency directly leads to that in the detection efficiency. In other words, however, there is still a room for improvement. We examine various process in the detector, and estimate the major loss is primarily that of scintillation light in a plastic scintillator pillar with a very small cross section (2.68mm squared) and a long length (40mm). Nevertheless, the current model provides the MDP of 6% for 10mCrab sources, which are the targets of PolariS.
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.
PolariS (Polarimetry Satellite) is a Japanese small satellite mission dedicated to polarimetry of X-ray and γ-ray sources. The primary aim of the mission is to perform hard X-ray (10-80 keV) polarimetry of sources brighter than 10 mCrab. For this purpose, PolariS employs three hard X-ray telescopes and scattering type imaging polarimeters. PolariS will measure the X-ray polarization for tens of sources including extragalactic ones mostly for the first time. The second purpose of the mission is γ-ray polarimetry of transient sources, such as γ-ray bursts (GRBs). Wide field polarimeters based on similar concept as that used in the IKAROS/GAP but with higher sensitivity will be used, and polarization measurement of 10 GRBs per year is expected.
X-ray CCD operated onboard satellite are contaminated by outgas from organic material used in satellites. This contamination causes a significant reduction in the detection sensitivity of X-ray detectors.
In order to prevent such contamination to the Back-Illuminated CCD (BI-CCD) of the Soft X-ray Imager
(SXI) onboard ASTRO-H, we have developed a Contamination Blocking Filter (CBF), which consists of ~30nm thick Aluminum and ~200nm thick Polyimide. The CBF is be placed on the top of the CCD camera hood and is required to have a high X-ray transmission in order to take advantage of the high detection efficiency of BI-CCD.
We measured the X-ray transmission of three flight candidates of the CBF last October at the SPring-8 and obtained the X-ray transmission of three CBFs in the soft X-ray energy from 0.2 to 1.8 keV which covers the absorption edges around C-K, N-K, O-K, and Al-K including X-ray absorption fine structure (XAFS). In these measurements, we found three CBFs have high X-ray transmission below 2ke V, e.g. ~70% at around 0.5 keV, and determined the thickness of Al and Polyimide to be 220 nm and ~50 nm, respectively. We will calculate the response function of SXI including these results.
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.
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.
PolariS (Polarimetry Satellite) is a Japanese small satellite mission dedicated to polarimetry of X-ray and γ-ray sources. The primary aim of the mission is to perform wide band X-ray (4-80 keV) polarimetry of sources brighter than 10 mCrab. For this purpose, Polaris employs three hard X-ray telescopes and two types of focal plane imaging polarimeters. PolariS observations will measure the X-ray polarization for tens of sources including extragalactic ones mostly for the first time. The second purpose of the mission is γ-ray polarimetry of transient sources, such as γ-ray bursts. Wide field polarimeters based on similar concept as that used in the IKAROS/GAP but with higher sensitivity, i.e., polarization measurement of 10 bursts per year, will be employed.
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 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.
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 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-.
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.
The Soft X-ray Imager (SXI) is the X-ray CCD camera on board the NeXT mission that is to be launched around 2013. We are going to employ the CCD chips developed at Hamamatsu Photonics, K.K. We have been developing two types of the CCD: an N-channel chip and a P-channel chip. The effective area of the detector system will be 5-6 cm square with a depletion layer of 100-200μm. The P-channel chip will have thicker depletion layer that makes it easy to develop it to back-illuminated type CCD. It will need a year or so for us to reach the final conclusion which type will be available. Based on the Suzaku experience, we will incorporate the charge injection gate so that we can reduce the proton damage. Furthermore, we will employ a mechanical cooler to keep the CCD working temperature down to -120°C in spite that NeXT will be in the low earth orbit. We can expect the radiation damage on our system very small. The CCD will have an Al coat on the chip to prevent optical photons from entering. This also eliminates the vacuum-tight chamber and the door-opening mechanism. We are planning to employ a custom-made analog ASIC that will reduce the power consumption and the size. The ASIC may speed up the frame-time if we can use a multi-node CCD. With using the focal length of 6m, the SXI will fully function with the optics around 20" resolution. We will report the current plan of the SXI in detail.
We are planning to have a "formation flight all sky telescope"~(FFAST) that will cover a large sky area in relatively high energy X-ray. In particular, it will focus on the energy range above 10 keV. It consists of two small satellites that will go in a formation flight. One is an X-ray telescope satellite and the other is a detector satellite. Two satellites will be simultaneously launched by a single rocket vehicle into a low earth orbit. They are in a formation flight with a separation of 20m±10cm. The observation direction is determined by the two satellites. Since two satellites are put into Keplerian orbit, the observation direction is scanning the sky rather than pointing to a fixed direction.
The X-ray telescope satellite carries one super-mirror covering the energy range up to 80 keV. The telescope is 45-cm diameter and its focal length is 20m. The telescope is a "super mirror" ~that has a multi-layer coating covering the energy range up to 80 keV. The effective area is about 500cm2 at low energy and 200cm2 at 70 keV. The mirror system is a thin foil mirror that is developing at Nagoya University that is being developed. The PSF of the mirror will be about 1-2 arcmin. The satellite is equipped with an attitude control system using momentum wheel. It will keep the satellite such that the optical axis of the mirror is pointing to the detector satellite. The other is a detector satellite that carries an SDCCD system. The SDCCD is a CCD with a scintillator that is directly attached to the CCD. The CCD chip is fully depleted which can be a back-illuminated CCD. The scintillator is attached to the CCD at back side so that it has high detection efficiency for visible photons generated inside the scintillator. The X-ray enters into the CCD at front side. Therefore, low energy X-rays (below 10 keV) can be photo-absorbed in the depletion layer of the CCD while high energy X-rays will be absorbed in the scintillator that will emit visible photons The visible photons can be detected by the CCD. Depletion layer events usually form small charge spread while scintillator events usually form large charge spread. These events generate charge spread in a symmetric form with different size.
On the contrary, charged particles leave an elongated charge spread that can be distinguished from X-ray events by pattern recognition. This project, Formation Flight All Sky Telescope (FFAST), will scan a large sky area at hard X-ray region.
The NeXT (New exploration X-ray Telescope), the new Japanese X-ray Astronomy Satellite following Suzaku,
is an international X-ray mission which is currently planed for launch in 2013. NeXT is a combination of wide
band X-ray spectroscopy (3-80 keV) provided by multi-layer coating, focusing hard X-ray mirrors and hard
X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-10 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 and a non-focusing soft gamma-ray detector. With these instruments, NeXT
covers very wide energy range from 0.3 keV to 600 keV. The micro-calorimeter system will be developed by
international collaboration lead by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with
high spectral resolution of ΔE ~7 eV by the micro-calorimeter will enable a wide variety of important science
themes to be pursued.
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.
Since the launch of the Suzaku X-ray astronomy satellite into low- earth orbit in July, 2005, the performance
of the CCD detectors in the X-ray Imaging Spectrometer (XIS) detectors have slowly degraded, as expected,
due to accumulating radiation damage. We compare the evolution of front- and back-illuminated XIS CCDs
with one another and with that of very similar detectors installed in the ACIS instrument aboard the Chandra
X-ray Observatory, which is in a much higher orbit than Suzaku. We attempt to identify effects of the differing
radiation environments as well as those arising from structural differences between the two types of detector.
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.
We have been developing a hard X-ray polarimeter to open a new window for hard X-ray astronomy. The project is
called as PHENEX (Polarimetry for High ENErgy X rays). The PHENEX detector is Compton scattering type
polarimeter and it is constructed by several unit counters. The unit counter can achieve the modulation factor and the
detection efficiency of 53% and 20% at 80 keV, respectively. Installing four unit counters, we have carried out balloon-borne
experiment in Jun.13 2006 to preliminarily observe the polarization of the Crab Nebula in hard X-ray band. The
PHENEX polarimeter successfully operated on the level flight and observed the Crab Nebula for about one hour. From
the analysis of the obtained data, it was recognized that the PHENEX polarimeter does not make much spurious
modulation and that the ratio of the signal from the Crab Nebula to the background from the blank sky is 1:3. Though we
can not precisely determine the degree and the direction of the polarization for the Crab Nebula because of the trouble of
the attitude control system, the obtained results were not inconsistent with those in the X-ray band. We will carry out
balloon-borne experiment again, fixing the trouble of the attitude control system.
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.
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.
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.
We give overview and the current status of the development of the Soft X-ray Imager (SXI) onboard the NeXT
satellite. SXI is an X-ray CCD camera placed at the focal plane detector of the Soft X-ray Telescopes for Imaging
(SXT-I) onboard NeXT. The pixel size and the format of the CCD is 24 x 24μm (IA) and 2048 x 2048 x 2
(IA+FS). Currently, we have been developing two types of CCD as candidates for SXI, in parallel. The one is
front illumination type CCD with moderate thickness of the depletion layer (70 ~ 100μm) as a baseline plan.
The other one is the goal plan, in which we develop back illumination type CCD with a thick depletion layer
(200 ~ 300μm). For the baseline plan, we successfully developed the proto model 'CCD-NeXT1' with the pixel
size of 12μm x 12μm and the CCD size of 24mm x 48mm. The depletion layer of the CCD has reached 75 ~ 85μm.
The goal plan is realized by introduction of a new type of CCD 'P-channel CCD', which collects holes in stead
of electrons in the common 'N-channel CCD'. By processing a test model of P-channel CCD we have confirmed
high quantum efficiency above 10 keV with an equivalent depletion layer of 300μm. A back illumination type
of P-channel CCD with a depletion layer of 200μm with aluminum coating for optical blocking has been also
successfully developed. We have been also developing a thermo-electric cooler (TEC) with the function of the
mechanically support of the CCD wafer without standoff insulators, for the purpose of the reduction of thermal
input to the CCD through the standoff insulators. We have been considering the sensor housing and the onboard
electronics for the CCD clocking, readout and digital processing of the frame date.
The NeXT mission has been proposed to study high-energy non-thermal phenomena in the universe. The high-energy response of the super mirror will enable us to perform the first sensitive imaging observations up to 80 keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixelated CdTe detector, will provide spectra and images in the wide energy range from 0.5 keV to 80 keV. In the soft gamma-ray band upto ~1 MeV, a narrow field-of-view Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several x 10-8 photons/s/keV/cm2 in the hard X-ray region and a few x 10-7 photons/s/keV/cm2 in the soft gamma-ray region.
We present the current status of soft X-ray calibration of X-ray CCD cameras, X-ray Imaging Spectrometer (XIS), onboard Astro-E2. We perform soft X-ray calibration of four front illuminated (FI) CCD cameras and two back illuminated (BI) CCD cameras, among which four cameras will be selected to be installed on the satellite. The calibration aims to measure the quantum efficiency and re-distribution function of the CCDs as a function of incident X-ray energy. A soft X-ray spectrometer is used to measure these items. In addition, we employ a gas proportional counter and an XIS engineering unit as reference detectors for the quantum efficiency measurement. We describe how we calibrate the absolute quantum efficiency of the XIS using these instruments. We show some of the preliminary results of the calibration including quick look results of BI CCD cameras.
We make a plan of a hard X-ray polarimetry experiment with a small satellite. Bright point-like sources in 20-80keV are prime targets, for which we will not use focusing optics. Comparing various types of polarimeters, we adopt a scattering type in which anisotropy in scattering directions of photons is employed. After optimization of the design is considered with simplified models of scattering polarimeters, we propose to use segmented scatter targets made of plastic scintillators, with which scattering location is identified by detecting recoiled electrons. Simulations show that recoiled electrons are detectable when incident X-ray energies are above 40keV, for which higher polarimetry sensitivity is obtained. We confirmed the performance of such a polarimeter in experiments at a Synchrotron facility and performed a balloon flight in which a proto type unit of the polarimeter was onboard. We finally discuss feasibility of a small satellite experiment in which many of the polarimeter units will be employed. Twenty five units of the polarimeter enable us to detect hard X-ray polarization of 5-10% for a hundred mCrab sources. Improvement in the sensitivity to detect recoiled electrons will significantly improve the polarimetry sensitivity. We also consider a low energy extension of our system down to below 10keV in order to cover wide energy range.
The X-ray Imaging Spectrometer (XIS) on the Astro-E2 mission contains
X-ray CCDs fabricated at MIT Lincoln Laboratory. We present results from CCD subassembly calibration of these detectors. Absolute detection efficiency and spectral resolution in the 0.3-10 keV band
are presented for four front-illuminated and two back-illuminated flight candidate devices. In addition, we characterize the charge injection capabilities of these devices. The quantum efficiency measurements have been used to model the various dead layers in the gate structure and to constrain the depletion depth of the detectors.
Noise levels of 2 electrons, RMS, and spectral resolution better than 50 eV (FWHM) at 525 eV have been achieved. The small but measurable charge transfer inefficiency (less than 1e-5 per transfer at 5.9 keV) of these devices has been characterized as a function of X-ray energy.
NeXT is the X-ray satellite proposed for the next Japanese space
science mission. While the satellite total mass and the launching
vehicle are similar to the prior satellite Astro-E2, the
sensitivity is much improved; it requires all the components to
be lighter and faster than previous architecture. This paper shows
the data processing architecture of the X-ray CCD camera system SXI
(Soft X-ray Imager), which is the top half of the WXI (Wide-band X-ray
Imager) of the sensitivity in 0.2-80keV. The system is basically
a variation of Astro-E2 XIS, but event extraction speed is much faster
than it to fulfill the requirements coming from the large effective area and fast exposure period. At the same time, data transfer lines
between components are redesigned in order to reduce the number
and mass of the wire harnesses that limit the flexibility of the
component distribution.
We measured optical and soft X-ray transmission of Optical Blocking Filters (OBFs) for Charge Coupled Device (CCD) cameras, which will be launched as focal plane detectors of X-ray telescopes onboard the Japanese 5th X-ray astronomical satellite, Astro-E 2. The filters were made from polyimide coated with Al. The X-ray absorption fine structures (XAFSs) at the K edges of C, N, O and K and L edges of Al were measured. The depth of the absorption edge of O was deep, compared to the other elements of polyimide. This is evidence of the oxidation of Al. The optical transmission is roughly less than 10-6 except for a peak around the wave length of 550 nm. Long term change of the soft X-ray transmission was measured. No significant change of the thickness of the oxidation layer was found during half year.
We propose a new method for absolute calibration of detection efficiency of X-ray detector. The method utilizes measurements with different X-ray incident angles. We first introduce the idea of the method, slant incidence method, in a simplified example. Secondly, we apply the method to measure a filter thickness, using the X-ray CCD camera and a 55Fe isotope source in order to verify our idea. The slant incidence method functions as we expected, but contradiction as large as 30% is observed against the estimates by conventional on-off method. Finally, we apply the slant incidence method to measure the build-in dead layer thickness of an X-ray CCD. using the X-ray spectrometer as a source. We got reasonable estimates for the thickness of the dead layer. An X-ray spectrometer is used to get the ratio of detected intensity of 45"a incidence to that of 0"a incidence as a function of X-ray energy. We get reasonable estimates for the thicknesses of two kinds of dead layers, SiO2 and Si. Discussion on advantages and limitations of this method, and future prospect is mentioned shortly.
We report on design updates for the XIS (X-ray Imaging Spectrometer)
on-board the Astro-E2 satellite. Astro-E2 is a recovery mission of Astro-E, which was lost during launch in 2000. Astro-E2 carries a total of 5 X-ray telescopes, 4 of which have XIS sensors as their focal plane detectors. Each XIS CCD camera covers a field of view of 19×19 arcmin in the energy range of 0.4-12 keV. The design of the Astro-E2 XIS is basically the same as that for Astro-E, but some improvements will be implemented. These are (1) CCD charge injection capability, (2) a revised heat-sink assembly, and (3) addition of a 55Fe radio-isotope on the door. Charge injection may be used to compensate for and calibrate radiation-induced degradation of the CCD charge transfer efficiency. This degradation is expected to become significant after a few year's operation in space. The new heat-sink assembly is expected to increase the mechanical reliability and cooling capability of the XIS sensor. The new radio-isotope on the door will provide better calibration data. We present details of these improvements and summarize the overall design of the XIS.
We measure the polarization degree of monochromatic X-rays from an electron impact type X-ray generator through a double crystal spectrometer. The double crystal spectrometer is installed so that it enhances the polarization from the generator by its different efficiency for (pi) and (sigma) polarized X-rays. Measurement is performed for applied high voltage (HV) of 20 kV to 50 kV, and monochromatic X-ray energy in the unit of keV (Ex) of 0.7 to 0.9 times HV. We obtain the polarization degree of 0.48 and 0.41 for HV equals 20 and HV equals 50 with Ex/HV equals 0.9. We also measure the polarization degree of direct beam without the monochrometer, comparing the polarization boosting factor by crystals measured with theoretical model. The system is good for getting moderate intensity of partially polarized monochromatic X-ray beam.
We measure various spectral response characteristics around the oxygen and silicon K absorption edges of a Charge- Coupled Device X-ray detector used in the X-ray Imaging Spectrometer developed for the ASTRO-E mission. We have evaluated X-ray Absorption Fine Structure (XAFS) around oxygen K edge in detail. A strong absorption peak of 45% is confirmed just above the oxygen K edge and an oscillatory structure follows whose amplitude decreases from 20% at the edge to less than 1% at 0.9 keV. We also show XAFS and discuss on a change of the response function around the silicon K edge. The discontinuity of the signal pulse height at the silicon K edge is less than 1.8 eV. We determine the thickness of silicon, silicon dioxide, and silicon nitride in the dead layer using the depth of the absorption edge.
Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured with a grating spectrometer system at Osaka. First, relation between incident X-ray energy and output pulse height peak (E-PH relation) is examined with an SX grating. It is found that jump in the E-PH relation around Si-K edge is at most 2.7 eV. Second, quantum efficiency (QE) of the XIS in 0.4 - 2.2 keV range is measured relatively to the reference CCD of which absolute QE was calibrated with a gas proportional counter. The QE is fitted with a model in which CCD gate structures are considered. Systematic error on the QE results is estimated by referring an independent measurement. Third, tuning and improvement of the response function is performed. We employ six components to reproduce the response profile of the XIS. In this paper, improvement of one component which is originated in the events absorbed in the channel-stop is presented. Nevertheless, Astro-E was lost due to the launch failure. We overview the XIS project in its flight model phase, modified points of the design, problems and solutions etc., in order to be utilized in a possible recovery of the satellite.
The ASTRO-E X-ray Imaging Spectrometers (XISs) consists of four sets of X-ray CCD camera for the ASTRO-E mission. The XISs have been calibrated at Osaka University, Kyoto University, ISAS and MIT. The calibration experiment at Osaka focuses on the soft x-ray response of the XIS. The calibration of the XIS flight model has been performed since August 1998. We measured the signal-pulse height, the energy resolution and the quantum efficiency of the XIS as a function of energy, all of which are essential to construct the response function of the XIS. The detailed shape of the pulse-height-distribution are also investigated. We also constructed a numerical simulator of the XIS, which tracks the physical process in the CCD so as to reproduce the measured data. With a help of this simulator, we propose a model of the pulse-height-distribution of the XIS for single energy incident x-rays. The model consists of four components; two Gaussians, a constant, plus a triangle-shape component.
Monitor of All-Sky X-ray Image (MAXI) is the first astrophysical payload for the Japanese Experiment Module (JEM) on the International Space Station. It is designed for monitoring all sky in the x-ray band. Two kinds of x-ray detectors, the gas slit camera and the solid-state slit camera, are employed. The former is the gas proportional counter with 1D position sensitivity and the latter is the x-ray CCD. We have designed and constructed the engineering models of both detectors. We have also developed an x-ray irradiation facility in the Tsukuba Space Center of National Space Development Agency of Japan. We report the status of the mission and introduce the x-ray irradiation facility.
We report the x-ray quantum efficiency of the XIS in the soft x-ray band between 0.5 keV and 2.2 keV. We also report the x-ray and optical transmission of the OBF. We obtained the quantum efficiency of the XIS of approximately 0.25 at 0.53 keV. We also obtained the x-ray transmission of approximately 0.65 at O K(alpha) and optical transmission below 5 X 10-5 in the range 400-950 nm.
A mesh experiment for the x-ray CCD enables us to specify the interaction position of the x-ray photon with subpixel resolution. There are two types of experiments: a single- pitch mesh experiment and a multi-pitch mesh experiment. Using the multipitch mesh experiment, we have established the method to measure the charge cloud shape inside the CCD produced by an x-ray photon. We can measure signal outputs from the pixel according to the interaction position of x- rays. Finally, we obtain, in detail, the charge cloud shape which can be well represented by an asymmetric Gaussian function. The symmetry of the charge cloud shape is probably due to the asymmetry of the electric field inside the CCD.
The x-ray imaging spectrometers (XIS) are x-ray CCD cameras on-board the Astro-E satellite launched in 2000. The XIS consists of 4 cameras, each of them will be installed on a focal plane of the Astro-E X-ray Telescope (XRT). The XIS not only have a higher sensitivity, which comes from a larger effective area of the XRT and thicker depletion layers of the XIS CCDs, than ASCA SIS. But also have several features that will overcome the radiation damage effects anticipated in the orbit. The calibration experiment at Osaka focuses on the soft x-ray response of the XIS. The calibration system employs a grating spectrometer which irradiates the CCD with dispersed x-rays. We have obtained preliminary results on the XIS proto model, including the energy-pulse-height relation, the energy-resolution relation, and the quantum efficiency at the energy range of 0.25-2.2 keV.
NASDA (National Space Development Agency of Japan) has selected MAXI as an early payload of the JEM (Japanese experiment module) Exposed Facility (EF) on the space station. MAXI is designed for all sky x-ray monitoring, and is the first astrophysical payload of four sets of equipment selected for JEM. MAXI will monitor the activities of about 1000 - 2000 x-ray sources. In the present design, MAXI is a slit scanning camera system which consists of two kinds of x-ray detectors; one with one-dimensional position sensitive proportional counters and the other with an x-ray CCD array employed for one-dimensional imaging. MAXI will be able to detect one milli-Crab x-ray sources in a few-day observations. The whole sky will be covered completely in every orbit of the space station. MAXI will be capable of monitoring variability of galactic and extragalactic sources on timescales of days with a sensitivity improvement of a factor of 5 or more over previous missions. NASDA and RIKEN have jointly begun the design and construction of MAXI. The payload will be ready for launch in 2003. In this paper we present the scientific objectives of MAXI, a basic design and some simulation results, after introducing the present status of JEM.
We report here the results of polarized X-ray detection with a charge-coupled device (CCD). The photoelectron produced in the CCD is mainly ejected along the electric vector of the incident X-ray. This means that the primary charge cloud mainly remains in the depletion layer if the photo absorption occurs in it. Therefore, a primary charge cloud is elongated towards the X-ray polarization vector. The range of the electron in the silicon is roughly expressed (E/10 keV)1.75 micrometers where E is the electron energy in KeV. Therefore, the range of the photoelectron in this energy region is at most two-pixel length. We investigated the relation between the direction of the linear polarization of X-rays and the statistics of the charge cloud shape.
The x-ray optical properties of X-Ray Telescopes (XRTs) on board Asca were evaluated with an x-ray pencil beam at ISAS 30 m x-ray beam line. The total effective area of four XRTs is obtained to be about 1300 cm2, 800 cm2, and 450 cm2 at each energy of 1.5 keV, 4.5 keV, and 8.0 keV, respectively. These values are about 15% less than those calculated by ray tracing method in an ideal case. The shadow effect of closely packed foils might be the main reason for the degradation of effective area. The Point Spread Function of XRT was also measured by an x-ray CCD. We have also measured the contamination of stray light, which were caused by the one time reflected photons (by primary or secondary mirror) and photons reflected on the back side surface of the mirror shells. The stray light profile and intensity were consistent to the results simulated by the ray tracing.
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