研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 准教授国立大学法人総合研究大学院大学 物理科学研究科 宇宙科学専攻 准教授
- 学位
- 博士（理学）(2003年3月 京都大学)修士（理学）(2000年3月 京都大学)
- 連絡先
- tsujimot
astro.isas.jaxa.jp - 研究者番号
- 10528178
- ORCID ID
https://orcid.org/0000-0002-9184-5556- J-GLOBAL ID
- 201801010256574610
- Researcher ID
- ABC-6667-2020
- researchmap会員ID
- B000296937
- 外部リンク
経歴
5-
2019年6月 - 現在
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2008年7月 - 2019年5月
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2007年1月 - 2009年7月
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2005年4月 - 2006年12月
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2003年4月 - 2005年3月
学歴
3-
2000年4月 - 2003年3月
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1998年4月 - 2000年3月
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1994年4月 - 1998年3月
委員歴
1-
2021年4月 - 2023年3月
論文
212-
The Astrophysical Journal 965(2) 135-135 2024年4月1日 査読有り
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Astrophysical Journal 960(1) 2024年1月1日Supersoft X-ray sources (SSSs) are white dwarf (WD) binaries that radiate almost entirely below ∼1 keV. Their X-ray spectra are often complex when viewed with the X-ray grating spectrometers, where numerous emission and absorption features are intermingled and hard to separate. The absorption features are mostly from the WD atmosphere, for which radiative transfer models have been constructed. The emission features are from the corona surrounding the WD atmosphere, in which incident emission from the WD surface is reprocessed. Modeling the corona requires different solvers and assumptions for the radiative transfer, which has yet to be achieved. We chose CAL87, an SSS in the Large Magellanic Cloud, which exhibits emission-dominated spectra from the corona, as the WD atmosphere emission is assumed to be completely blocked by the accretion disk. We constructed a radiative transfer model for the corona using two radiative transfer codes: xstar for a one-dimensional two-stream solver and MONACO for a three-dimensional Monte Carlo solver. We identified their differences and limitations in comparison to the spectra taken with the Reflection Grating Spectrometer on board the XMM-Newton satellite. We finally obtained a sufficiently good spectral model of CAL87 based on the radiative transfer of the corona plus an additional collisionally ionized plasma. In the coming X-ray microcalorimeter era, it will be required to interpret spectra based on radiative transfer in a wider range of sources than what is presented here.
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Astrophysical Journal 958(1) 2023年11月1日Circinus X-1 (Cir X-1) is a neutron star binary with an elliptical orbit of 16.6 days. The source is unique for its extreme youth, providing a key to understanding early binary evolution. However, its X-ray variability is too complex to reach a clear interpretation. We conducted the first high-cadence (every 4 hr, on average) observations covering one entire orbit using the NICER X-ray telescope. The X-ray flux behavior can be divided into stable, dip, and flaring phases. The X-ray spectra in all phases can be described by a common model consisting of a partially covered disk blackbody emission and the line features from a highly ionized photoionized plasma. The spectral change over the orbit is attributable to rapid changes of the partial covering medium in the line of sight and gradual changes of the disk blackbody emission. Emission lines of H- and He-like Mg, Si, S, and Fe are detected, most prominently in the dip phase. The Fe emission lines change to absorption in the course of the transition from the dip phase to the flaring phase. The estimated ionization degree indicates no significant changes, suggesting that the photoionized plasma is stable over the orbit. We propose a simple model in which the disk blackbody emission is partially blocked by a local medium in the line of sight that has spatial structures depending on the azimuth of the accretion disk. Emission lines upon the continuum emission are from the photoionized plasma located outside of the blocking material.
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Journal of Low Temperature Physics 211(5-6) 426-433 2023年6月Low-temperature detectors often use mechanical coolers as part of the cooling chain in order to reach sub-Kelvin operating temperatures. The microphonic noise caused by the mechanical coolers is a general and inherent issue for these detectors. We have observed this effect in the ground test data obtained with the Resolve instrument to be flown on the XRISM satellite. Resolve is a cryogenic X-ray microcalorimeter spectrometer with a required energy resolution of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient temperature to ∼ 4 K: four two-stage Stirling coolers (STC) driven nominally at 15 Hz and a Joule–Thomson cooler (JTC) driven nominally at 52 Hz. In 2019, we operated the flight-model instrument for two weeks, in which we also obtained accelerometer data inside the cryostat at a low-temperature stage (He tank). X-ray detector and accelerometer data were obtained continuously while changing the JTC drive frequency, which produced a unique data set for investigating how the vibration from the cryocoolers propagates to the detector. In the detector noise spectra, we observed harmonics of both STCs and JTC. More interestingly, we also observed the low (< 20 Hz) frequency beat between the 4th JTC and 14th STC harmonics and the 7th JTC and the 23–24th STC harmonics. We present here a description and interpretation of these measurements.
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Astrophysical Journal 945(2) 2023年3月1日MAXI J1820+070 is a transient black hole binary discovered on 2018 March 11. The unprecedented rich statistics brought by the NICER X-ray telescope allow detailed timing analyses up to ∼1 kHz uncompromised by photon shot noise. To estimate the time lags, a Fourier analysis was applied, which led to two different conclusions for the system configuration: one supporting a lamp-post configuration with a stable accretion disk extending close to the innermost stable circular orbit and the other supporting a truncated accretion disk contracting with time. Using the same data set, we present the results based on the cross-correlation function (CCF). The CCF is calculated between two different X-ray bands where one side is subtracted from the other side, which we call the differential CCF (dCCF). Soft and hard lags of ∼0.03 and 3 s, respectively, are clearly identified without being diluted by the spectral mixture, demonstrating the effectiveness of the dCCF analysis. The evolution of these lags is tracked, along with spectral changes for the first 120 days since discovery. Both the dCCF and spectral fitting results are interpreted as the soft lag being a reverberation lag between the Comptonized emission and the soft excess emission, and that the hard lag is between the disk blackbody emission and the Comptonized emission. The evolutions of these lags are in line with the picture of a truncated disk contracting with time.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 75(1) 177-186 2023年2月gamma Cas analog sources are a subset of Be stars that emit intense and hard X-ray emission. Two competing ideas for their X-ray production mechanism are (a) the magnetic activities of the Be star and its disk and (b) the accretion from the Be star to an unidentified compact object. Among such sources, pi Aqr plays a pivotal role as it is one of the only two spectroscopic binaries observed for many orbital cycles and one of the three sources with X-ray brightness sufficient for detailed X-ray spectroscopy. Bjorkman et al. (2002, ApJ, 573, 812) estimated the secondary mass > 2.0 M-? with optical spectroscopy, which would argue against the compact object being a white dwarf (WD). However, their dynamical mass solution is inconsistent with an evolutionary solution and their radial velocity measurement is inconsistent with later work by Naze et al. (2019, A & A, 632, A23). We revisit this issue by adding a new data set with the NuSTAR X-ray observatory and the HIDES echelle spectrograph. We found that the radial velocity amplitude is consistent with Naze et al. (2019, A & A, 632, A23), which is only half of that claimed by Bjorkman et al. (2002, ApJ, 573, 812). Fixing the radial velocity amplitude of the primary, the secondary mass is estimated as < 1.4 M(? )over an assumed range of the primary mass and the inclination angle. We further constrained the inclination angle and the secondary mass independently by fitting the X-ray spectra with a non-magnetic or magnetic accreting WD model under the assumption that the secondary is indeed a WD. The two results match well. We thus argue that the possibility of the secondary being a WD should not be excluded for pi Aqr.
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Ground test results of the electromagnetic interference for the x-ray microcalorimeter onboard XRISMJournal of Astronomical Telescopes, Instruments, and Systems 9(1) 18004 2023年1月1日Electromagnetic interference (EMI) for low-temperature detectors is a serious concern in many missions. We investigate the EMI caused by the spacecraft components to the x-ray microcalorimeter of the Resolve instrument onboard the x-ray imaging and spectroscopy mission, which is currently under development by an international collaboration and is planned to be launched in 2023. We focus on the EMI from (a) the low-frequency magnetic field generated by the magnetic torquers (MTQ) used for the spacecraft attitude control and (b) the radio-frequency (RF) electromagnetic field generated by the S and X band antennas used for communication between the spacecraft and the ground stations. We executed a series of ground tests both at the instrument and spacecraft levels using the flight-model hardware in 2021-2022 in a JAXA facility in Tsukuba. We also conducted electromagnetic simulations partially using the Fugaku high-performance computing facility. The MTQs were found to couple with the microcalorimeter, which we speculate through pick-ups of low-frequency magnetic field and further capacitive coupling. There is no evidence that the resultant energy resolution degradation is beyond the current allocation of noise budget. The RF communication system was found to leave no significant effect. We present the result of the tests and simulation in this article.
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Journal of Astronomical Telescopes, Instruments, and Systems 9(1) 14003 2023年1月1日Resolve is a payload hosting an x-ray microcalorimeter detector operated at 50 mK in the x-ray imaging and spectroscopy mission. It is currently under development as part of an international collaboration and is planned to be launched in 2023. A primary technical concern is the microvibration interference in the sensitive microcalorimeter detector caused by the spacecraft bus components. We conducted a series of verification tests in 2021 to 2022 on the ground, the results of which are reported here. We defined the microvibration interface between the spacecraft and the Resolve instrument. In the instrument-level test, the flight-model hardware was tested against the interface level by injecting it with microvibrations and evaluating the instrument response using the 50 mK stage temperature stability, adiabatic demagnetization refrigerator magnet current consumption rate, and detector noise spectra. We found strong responses when injecting microvibration at 1/4200, 380, and 610 Hz. In the former two cases, the beat between the injected frequency and cryocooler frequency harmonics were observed in the detector noise spectra. In the spacecraft-level test, the acceleration and instrument responses were measured with and without suspension of the entire spacecraft. The reaction wheels (RWs) and inertial reference units (IRUs), two major sources of microvibration among the bus components, were operated. In conclusion, the observed responses of Resolve are within the acceptable levels in the nominal operational range of the RWs and IRUs. There is no evidence that the resultant energy resolution degradation is beyond the current allocation of noise budget.
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Journal of Low Temperature Physics 211(5-6) 384-397 2022年12月2日LiteBIRD is a future satellite mission designed to observe the polarization of the cosmic microwave background radiation in order to probe the inflationary universe. LiteBIRD is set to observe the sky using three telescopes with transition-edge sensor bolometers. In this work we estimated the LiteBIRD instrumental sensitivity using its current design. We estimated the detector noise due to the optical loadings using physical optics and ray-tracing simulations. The noise terms associated with thermal carrier and readout noise were modeled in the detector noise calculation. We calculated the observational sensitivities over fifteen bands designed for the LiteBIRD telescopes using assumed observation time efficiency.
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Journal of Low Temperature Physics 209(5-6) 1097-1103 2022年12月The radio frequency interference (RFI) due to the X-band telecommunication with the LiteBIRD spacecraft was computed using a 3D electromagnetic field simulator to evaluate its field strength at the instrument detectors. First, the level of RFI with different materials for the spacecraft main body was evaluated. The attenuation effects for aluminum (Al) and carbon-fiber-reinforced plastic (CFRP) in comparison with a perfect electric conductor (PEC) were 1.5 dB and 10.5 dB, respectively. Then, the electric field strength for various shield plate structures on the solar panels was evaluated. In the best case, the RFI level could be attenuated by another 31 dB with an optimum design. Finally, the frequency dependence of the RFI was evaluated across the X-band, giving an attenuation slope of − 10 dB/oct, leading to an electric field intensity of − 116.8 dBV/m at the detector position for a frequency of 8.4 GHz.
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Progress of Theoretical and Experimental Physics 2023(4) 2022年11月21日Abstract LiteBIRD the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun-Earth Lagrangian point L2, where it will map the cosmic microwave background (CMB) polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of 2.2 μK-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions and synergies with other projects. Subject Index LiteBIRD cosmic inflation, cosmic microwave background, B-mode polarization, primordial gravitational waves, quantum gravity, space telescope
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Journal of Low Temperature Physics 209(3-4) 396-408 2022年11月Feedhorn- and orthomode transducer- (OMT) coupled transition edge sensor (TES) bolometers have been designed and micro-fabricated to meet the optical specifications of the LiteBIRD high frequency telescope (HFT) focal plane. We discuss the design and optical characterization of two LiteBIRD HFT detector types: dual-polarization, dual-frequency-band pixels with 195/280 GHz and 235/337 GHz band centers. Results show well-matched passbands between orthogonal polarization channels and frequency centers within 3% of the design values. The optical efficiency of each frequency channel is conservatively reported to be within the range 0.64- 0.72, determined from the response to a cryogenic, temperature-controlled thermal source. These values are in good agreement with expectations and either exceed or are within 10% of the values used in the LiteBIRD sensitivity forecast. Lastly, we report a measurement of loss in Nb/SiNx/Nb microstrip at 100 mK and over the frequency range 200–350 GHz, which is comparable to values previously reported in the literature.
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JOURNAL OF LOW TEMPERATURE PHYSICS 2022年11月The radio frequency interference (RFI) due to the X-band telecommunication with the LiteBIRD spacecraft was computed using a 3D electromagnetic field simulator to evaluate its field strength at the instrument detectors. First, the level of RFI with different materials for the spacecraft main body was evaluated. The attenuation effects for aluminum (Al) and carbon-fiber-reinforced plastic (CFRP) in comparison with a perfect electric conductor (PEC) were 1.5 dB and 10.5 dB, respectively. Then, the electric field strength for various shield plate structures on the solar panels was evaluated. In the best case, the RFI level could be attenuated by another 31 dB with an optimum design. Finally, the frequency dependence of the RFI was evaluated across the X-band, giving an attenuation slope of - 10 dB/oct, leading to an electric field intensity of - 116.8 dBV/m at the detector position for a frequency of 8.4 GHz.
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JOURNAL OF LOW TEMPERATURE PHYSICS 209(3-4) 686-692 2022年11月LiteBIRD is a space-borne experiment dedicated to detecting large-scale B-mode anisotropies in the linear polarization of the Cosmic Microwave Background (CMB) predicted by the theory of inflation. It is planned to be launched in the late 2020s to the second Lagrange point (L2) of the Sun-Earth system. LiteBIRD will map the sky in 15 frequency bands. In comparison with Planck HFI, the previous lowtemperature bolometer-based satellite for CMB observations, the number of detector has increased by two orders of magnitude, up to similar to 5000 detectors in total. The data rate is 19 Hz from each detector. The bandpass to the ground is limited to 10 Mbps using the X-band for a few hours per day. These require the data to be compressed by more than 50%. The exact value depends on how much information entropy is contained in the real data. We have thus evaluated the compression by simulating the time-ordered data of polarization-sensitive bolometers. The foreground emission, detector noise, cosmic ray glitches, leakage from the CMB intensity to polarization, etc., are simulated. We investigated several algorithms and demonstrated that the required compression ratio can be achieved by some of them. We describe the details of this evaluation and propose algorithms that can be employed in the on-board digital electronics of LiteBIRD.
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Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray 12181 2022年8月31日The resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM) consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput x-ray mirror assembly (XMA) with a focal length of 5.6 m. XRISM is a recovery mission of ASTRO-H/Hitomi, and the Resolve instrument is a rebuild of the ASTRO-H soft x-ray spectrometer (SXS) and the Soft X-ray Telescope (SXT) that achieved energy resolution of a1/45 eV FWHM on orbit, with several important changes based on lessons learned from ASTRO-H. The flight models of the Dewar and the electronics boxes were fabricated and the instrument test and calibration were conducted in 2021. By tuning the cryocooler frequencies, energy resolution better than 4.9 eV FWHM at 6 keV was demonstrated for all 36 pixels and high resolution grade events, as well as energy-scale accuracy better than 2 eV up to 30 keV. The immunity of the detectors to microvibration, electrical conduction, and radiation was evaluated. The instrument was delivered to the spacecraft system in 2022-04 and is under the spacecraft system testing as of writing. The XMA was tested and calibrated separately. Its angular resolution is 1.27′ and the effective area of the mirror itself is 570 cm2 at 1 keV and 424 cm2 at 6 keV. We report the design and the major changes from the ASTRO-H SXS, the integration, and the results of the instrument test.
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Ground test results of the micro-vibration interference for the x-ray microcalorimeter onboard XRISMProceedings of SPIE - The International Society for Optical Engineering 12181 2022年Resolve is a payload hosting an x-ray microcalorimeter detector operated at 50 mK in the X-Ray Imaging and Spectroscopy Mission (XRISM), which is currently under development by an international collaboration and is planned to be launched in 2023. One of the technical concerns is the micro-vibration interference to the sensitive microcalorimeter detector by the spacecraft bus components. We verified this in a series of the ground tests in 2021–2022, the results of which are reported here. We defined the micro-vibration interface between the spacecraft and the Resolve instrument. In the instrument-level test, we tested the flight-model hardware against the interface level by injecting micro-vibration using vibrators and evaluated the instrument response using the 50 mK stage temperature stability, the ADR magnet current consumption rate, and the detector noise spectra. We found the strong responses when injecting micro-vibration at ∼200, 380, and 610 Hz. In the former two cases, the beat among the injected frequency and the cryocooler frequency harmonics are also observed in the detector noise spectra. In the spacecraft-level test, we measured the acceleration and the instrument responses with and without suspending the entire spacecraft. The reaction wheels and the inertial reference units, two major sources of micro-vibration among the bus components, were operated. We found that the observed Resolve responses are within acceptable levels.
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X-RAY, OPTICAL, AND INFRARED DETECTORS FOR ASTRONOMY X 12191 2022年The Resolve instrument onboard the XRISM satellite is equipped with 6 x 6 x-ray microcalorimeter detectors aiming at an energy resolution of 7 eV (FWHM) at 5.9 keV. It is currently under development by an international collaboration and will be launched in 2023. The detectors are operated at 50 mK, which is achieved by a combination of four Stirling coolers (STC), one Joule-Thomson cooler (JTC), three-stage adiabatic demagnetization refrigerators, and superfluid helium inside the dewar. The cryocoolers (STC and JTC) are significant sources of microphonic noise against the detector performance. To understand and characterize the microphonic propagation, we monitored the level of vibration throughout the ground instrument-level tests in 2019-2022, yielding a rich and unique data set of the accelerometers and the detector at 50 mK amounting to 1720 hours (6.2 Ms). In this article, we report the result of classifying thermal and non-thermal microcalorimeter noise, distinguishing the origin of the noise, and the method for optimizing the cooler drive frequency that minimizes the effect of the noise originating from the cooler.
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SPACE TELESCOPES AND INSTRUMENTATION 2022: ULTRAVIOLET TO GAMMA RAY 12181 2022年The spectroscopic performance of x-ray instruments can be affected at high count rates. The effects and mitigation in the optical chain, such as x-ray attenuation filters or de-focusing mirrors, are widely discussed, but those in the signal chain are not. Using the Resolve x-ray microcalorimeter onboard the XRISM satellite, we discuss the effects observed during high count rate measurements and how these can be modeled. We focus on three instrumental effects that impact performance at high count rate: CPU limit, pile up, and electrical cross talk. High count rate data were obtained during ground testing using the flight model instrument and a calibration x-ray source. A simulated observation of GX 13+1 is presented to illustrate how to estimate these effects based on these models for observation planning. The impact of these effects on high count rate observations is discussed.
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SPACE TELESCOPES AND INSTRUMENTATION 2022: ULTRAVIOLET TO GAMMA RAY 12181 2022年The Resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM) hosts an x-ray microcalorimeter that consists of 36 pixels in an array operated at 50 mK. It is currently under development and will be launched in 2022. X-ray microcalorimeters are known for their high spectral resolution, but they also excel in timing resolution for the necessity of cross-correlating event signals with templates in the time domain for accurate energy derivation. Primary and redundant modulated x-ray sources (MXS) are installed in Resolve for the purpose of correcting changes in the energy scale of the microcalorimeters while minimizing additional background; each source is switched on for intervals of O (1 ms) with a duty cycle of similar to 1 %. The MXS can also be utilized for calibrating relative timing as a function of pixel, event grade, and energy. We had a week-long run in 2022 June using the flight model hardware during the spacecraft level test with several different settings. We describe the method and the result of the relative timing calibration using this data set.
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SPACE TELESCOPES AND INSTRUMENTATION 2022: ULTRAVIOLET TO GAMMA RAY 12181 2022年Resolve is an X-ray microcalorimeter spectrometer on the X-Ray Imaging and Spectroscopy Mission (XRISM) to be launched in Japanese fiscal year 2022. Resolve is required to achieve an energy resolution of 7 eV at FWHM at 6 keV. To satisfy this requirement, it is necessary to correct the in-orbit gain drift. For this purpose, Resolve is equipped with multiple gain tracking calibration sources, including the modulated X-ray sources (MXS). The MXS will be operated in a pulsed mode, in which calibration X-rays illuminating the detector array are emitted at a duty cycle of similar to 1%. The low duty cycle allows us to monitor the gain drift with a small loss of the observing efficiency. However, the use of the MXS has drawbacks such as increase in the instrumental background due to exponentially decaying afterglow emission following each MXS pulse and the loss of throughput due to changes in the event-grade branching ratio. To minimize these effects, an optimization of the MXS operating parameters is needed. Based on the results of the MXS component-level tests, we established an analytical model that describes the MXS pulse and afterglow count rates. We obtained the optimal pulse parameters for various gain tracking intervals and estimated the effects of using the MXS on observation data. We further studied the trade-off between these effects and resolution degradation using the actual in-orbit drift observed with the Soft X-ray Spectrometer on the Hitomi satellite. Our study forms the basis of strategies for the in-orbit gain drift correction of Resolve.
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Ground test results of the electromagnetic interference for the x-ray microcalorimeter onboard XRISMSPACE TELESCOPES AND INSTRUMENTATION 2022: ULTRAVIOLET TO GAMMA RAY 12181 2022年Electromagnetic interference (EMI) for low-temperature detectors is a serious concern in many missions. We investigate the EMI caused by the spacecraft components to the x-ray microcalorimeter of the Resolve instrument onboard the X-Ray Imaging and Spectroscopy Mission (XRISM), which is currently under development by an international collaboration and is planned to be launched in 2023. We focus on the EMI from (a) the low-frequency magnetic field generated by the magnetic torquers used for the spacecraft attitude control and (b) the radio-frequency (RF) electromagnetic field generated by the S and X band antennas used for communication between the spacecraft and the ground stations. We executed a series of ground tests both at the instrument and spacecraft levels using the flight model hardware in 2021-2022 in a JAXA facility in Tsukuba. We also conducted electromagnetic simulations partially using the Fugaku high-performance computing facility. The magnetic torquers were found to couple with the microcalorimeter, but there is no evidence that the resultant degradation is beyond the current allocation of noise budget. The RF communication system was found to leave no significant effect. We present the result of the tests and simulation in this article.
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SPACE TELESCOPES AND INSTRUMENTATION 2022: OPTICAL, INFRARED, AND MILLIMETER WAVE 12180 2022年LiteBIRD is a space-borne experiment dedicated to detecting large-scale B-mode anisotropies of the linear polarization of the cosmic microwave background (CMB) predicted by the theory of inflation. It is planned to be launched in the late 2020s to the second Lagrangean point of the Sun-Earth system and map the sky in 15 frequency bands using thousands of transition edge sensor bolometers. LiteBIRD will be exposed to the cosmic-ray radiation throughout its lifetime, which may lead to the degradation of the scientific performance. Energy deposition by cosmic rays upon the focal plane bolometer detectors is considered a serious source of systematic effects. For a quantitative assessment of the effect, we present the result of Geant4 simulations to estimate the energy deposited by cosmic rays into the focal plane. We simulated different cosmic-ray components using CAD-based spacecraft models. We derive the spatial and energy distribution of the particles in the focal plane.
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Publications of the Astronomical Society of Japan 74(2) 283-297 2021年12月20日Presence of the apparently extended hard (2-10 keV) X-ray emission along the Galactic plane has been known since the early 1980s. With a deep X-ray exposure using the Chandra X-ray Observatory of a slightly off-plane region in the Galactic bulge, most of the extended emission was resolved into faint discrete X-ray sources in the Fe K band (Revnivtsev et al.,2009). The major constituents of these sources have long been considered to be X-ray active stars and magnetic cataclysmic variables (CVs). However, recent works including our NIR imaging and spectroscopic studies (Morihana et al.,2013, 2016) argue that other populations should be more dominant. To investigate this further, we conducted a much deeper NIR imaging observation at the center of the Chandra's exposure field. We have used the MOIRCS on the Subaru telescope, reaching the limiting magnitude of ~18 mag in the J, H, and Ks bands in this crowded region, and identified ~50 % of the X-ray sources with NIR candidate counterparts. We classified the X-ray sources into three groups (A, B, and C) based on their positions in the X-ray color-color diagram and characterized them based on the X-ray and NIR features. We argue that the major populations of the Group A and C sources are, respectively, CVs (binaries containing magnetic or non-magnetic white dwarfs with high accretion rates) and X-ray active stars. The major population of the Group B sources is presumably WD binaries with low mass accretion rates. The Fe K equivalent width in the composite X-ray spectrum of the Group B sources is the largest among the three and comparable to that of the Galactic bulge X-ray emission. This leads us to speculate that there are numerous WD binaries with low mass accretion rates, which are not recognized as CVs, but are the major contributor of the apparently extended X-ray emission.
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Journal of Cosmology and Astroparticle Physics 2021(9) 2021年9月Systematic effects arising from cosmic rays have been shown to be a significant threat to space telescopes using high-sensitivity bolometers. The LiteBIRD space mission aims to measure the polarised Cosmic Microwave Background with unprecedented sensitivity, but its positioning in space will also render it susceptible to cosmic ray effects. We present an end-to-end simulator for evaluating the expected scale of cosmic ray effects on the LiteBIRD space mission, which we demonstrate on a subset of detectors on the 166 GHz band of the Low Frequency Telescope. The simulator couples the expected proton flux at L2 with a model of the thermal response of the LFT focal plane and the electrothermal response of its superconducting detectors, producing time-ordered data which is projected into simulated sky maps and subsequent angular power spectra.
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Journal of Astronomical Telescopes, Instruments, and Systems 7(2) 2021年4月Resolve onboard the x-ray satellite X-Ray Imaging and Spectroscopy Mission (XRISM) is a cryogenic instrument with an x-ray microcalorimeter in a Dewar. A lid partially transparent to x-rays (called gate valve or GV) is installed at the top of the Dewar along the optical axis. Because observations will be made through the GV for the first few months, the x-ray transmission calibration of the GV is crucial for initial scientific outcomes. We present the results of our ground calibration campaign of the GV, which is composed of a Be window and a stainless steel mesh. For the stainless steel mesh, we measured its transmission using the x-ray beamline at ISAS. For the Be window, we used synchrotron facilities to measure the transmission and modeled the data with (i) photoelectric absorption and incoherent scattering of Be, (ii) photoelectric absorption of contaminants, and (iii) coherent scattering of Be changing at specific energies. We discuss the physical interpretation of the transmission discontinuity caused by the Bragg diffraction in polycrystal Be, which we incorporated into our transmission phenomenological model. We present the x-ray diffraction measurement on the sample to support our interpretation. The measurements and the constructed model meet the calibration requirements of the GV. We also performed a spectral fitting of the Crab nebula observed with Hitomi SXS and confirmed improvements of the model parameters.
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Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave 2020年12月21日
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Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X 11453 2020年12月16日LiteBIRD has been selected as JAXA's strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) B-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of-56 dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT: 34-161 GHz), one of LiteBIRD's onboard telescopes. It has a wide field-of-view (18° x 9°) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90a-▪ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.
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Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave 2020年12月15日
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Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave 2020年12月13日
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Cryogenics 108 2020年6月The X-ray Imaging and Spectroscopy Mission (XRISM) is a recovery mission of ASTRO-H (Hitomi) launched in 2016. The Resolve instrument on the XRISM is an 6 × 6 array of silicon-thermistor microcalorimeters cooled down to 50 mK combined with a 5.6 m focal length X-ray telescope. Its design inherits that of the Soft X-ray Spectrometer (SXS) onboard ASTRO-H that demonstrated high resolution spectroscopy of the X-ray microcalorimeters by observing astronomical objects and providing superb resolution spectra. The cooling chain of the Resolve consists of a 3-stage adiabatic demagnetization refrigerator (ADR), a Joule-Thomson cooler, ~30 L superfluid helium, four Stirling coolers and a vacuum vessel or a dewar. Design of the Resolve cooling system is basically the same as that in the SXS but several changes are adopted based on lessons learned. This paper describes mainly the cooling system from room temperature to about 1 K providing the ADR heat sink. Major changes include an aperture baffle for micrometeoroid and orbital debris protection and optical light reduction, an eddy current damper to slow a gate valve opening, a new vibration isolation system with launch-locks.
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Journal of Low Temperature Physics 199(3-4) 1107-1117 2020年5月1日Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite cosmic microwave background (CMB) polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA’s H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the CMB by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34 and 448 GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy’s foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5 K for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun–Earth Lagrangian point, L2, are planned for 3 years. An international collaboration between Japan, the USA, Canada, and Europe is sharing various roles. In May 2019, the Institute of Space and Astronautical Science, JAXA, selected LiteBIRD as the strategic large mission No. 2.
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Proceedings of SPIE - The International Society for Optical Engineering 11443 2020年The electromagnetic interference (EMI) is becoming an increasingly important factor in the spacecraft design equipped with highly sensitive detectors. This is particularly the case for LiteBIRD, in which the TES bolometers are exposed to space through the optical path. A particular concern is radiative interference caused by the X-band transmission during the ground communication. As the end-to-end verification test will be conducted in a later phase of the development, we need to derisk the concern early using simulation. In this report, we present the result of the EMI effects in the 1-GHz frequency range based on the electromagnetic simulation using a finite difference time domain (FDTD) solver. We modeled the dominant large structures of the spacecraft, calculated the spatial transmission of the antenna power, and estimated the electric field strength at the detector focal plane. The simulation results helped constrain aspects of the LiteBIRD satellite, such as the forward/backward ratio of the transmission antenna, to reduce the coupling between the antenna and the detectors.
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Proceedings of SPIE - The International Society for Optical Engineering 11443 2020年LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. JAXA selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with its expected launch in the late 2020s using JAXA's H3 rocket. LiteBIRD plans to map the cosmic microwave background (CMB) polarization over the full sky with unprecedented precision. Its main scientific objective is to carry out a definitive search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with an insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. To this end, LiteBIRD will perform full-sky surveys for three years at the Sun-Earth Lagrangian point L2 for 15 frequency bands between 34 and 448 GHz with three telescopes, to achieve a total sensitivity of 2.16 μK-arcmin with a typical angular resolution of 0.5° at 100 GHz. We provide an overview of the LiteBIRD project, including scientific objectives, mission requirements, top-level system requirements, operation concept, and expected scientific outcomes.
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Proceedings of SPIE - The International Society for Optical Engineering 11443 2020年LiteBIRD is a JAXA-led Strategic Large-Class mission designed to search for the existence of the primordial gravitational waves produced during the inflationary phase of the Universe, through the measurements of their imprint onto the polarization of the cosmic microwave background (CMB). These measurements, requiring unprecedented sensitivity, will be performed over the full sky, at large angular scales, and over 15 frequency bands from 34 GHz to 448 GHz. The LiteBIRD instruments consist of three telescopes, namely the Low-, Medium-and High-Frequency Telescope (respectively LFT, MFT and HFT). We present in this paper an overview of the design of the Medium-Frequency Telescope (89{224 GHz) and the High-Frequency Telescope (166{448 GHz), the so-called MHFT, under European responsibility, which are two cryogenic refractive telescopes cooled down to 5 K. They include a continuous rotating half-wave plate as the first optical element, two high-density polyethylene (HDPE) lenses and more than three thousand transition-edge sensor (TES) detectors cooled to 100 mK. We provide an overview of the concept design and the remaining specific challenges that we have to face in order to achieve the scientific goals of LiteBIRD.
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Proceedings of SPIE - The International Society for Optical Engineering 11453 2020年LiteBIRD has been selected as JAXA's strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) B-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of-56 dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT: 34-161 GHz), one of LiteBIRD's onboard telescopes. It has a wide field-of-view (18° x 9°) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90a-▪ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at 5 K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.
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Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年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 high-resolution X-ray spectroscopy. XRISM promises to discover new horizons in X-ray astronomy. XRISM carries a 6 x 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly and a co-aligned X-ray CCD camera that covers the same energy band over a large field of view. XRISM utilizes Hitomi heritage, but all designs were reviewed. The attitude and orbit control system were improved in hardware and software. The number of star sensors were increased from two to three to improve coverage and robustness in onboard attitude determination and to obtain a wider field of view sun sensor. The fault detection, isolation, and reconfiguration (FDIR) system was carefully examined and reconfigured. Together with a planned increase of ground support stations, the survivability of the spacecraft is significantly improved.
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Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年Resolve onboard the X-ray satellite XRISM is a cryogenic instrument with an X-ray microcalorimeter in a Dewar. A lid partially transparent to X-rays is installed at the top of the Dewar along the optical axis, which is called the gate valve (GV). Because observations will be made through the GV for the first few months, the X-ray transmission calibration of the GV is crucial for initial scientific outcomes. We present the results of our ground calibration campaign of the GV, which is composed of a Be window and a stainless steel mesh. For the stainless steel mesh, we measured its transmission using the X-ray beamline at ISAS for the first time. For the Be window, we used synchrotron facilities to measure the transmission and modeled the data with (i) photoelectric absorption and incoherent scattering of Be, (ii) photoelectric absorption of contaminants, and (iii) coherent scattering of Be. We discuss the physical interpretation of the transmission discontinuity caused by the Bragg diffraction in poly-crystal Be, which we incorporated into our phenomenological model. The measurements and the constructed model meet the calibration requirements of the GV. We also performed a spectral fitting of the Crab nebula data observed with Hitomi SXS and confirmed improvements of the model.
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Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年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 resolution to calibrate atomic codes, and cross-calibration between the XRISM instruments and with other observatories.
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Proceedings of SPIE - The International Society for Optical Engineering 11453 2020年The LiteBIRD satellite is planned to be launched by JAXA in the late 2020s. Its main purpose is to observe the large-scale B-mode polarization in the Cosmic Microwave Background (CMB) anticipated from the Inflation theory. LiteBIRD will observe the sky for three years at the second Lagrangian point (L2) of the Sun-Earth system. Planck was the predecessor for observing the CMB at L2, and the onboard High Frequency Instrument (HFI) suffered contamination by glitches caused by the cosmic-ray (CR) hits. We consider the CR hits can also be a serious source of the systematic uncertainty for LiteBIRD. Thus, we have started a comprehensive end-To-end simulation study to assess impact of the CR hits for the LiteBIRD detectors. Here, we describe procedures to make maps and power spectra from the simulated time-ordered data, and present initial results. Our initial estimate is that ClBB by CR is ∼ 2 ×10-6 μK2CMB in a one-year observation with 12 detectors assuming that the noise is 1 aW/ √ Hz for the differential mode of two detectors constituting a polarization pair.
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Proceedings of SPIE - The International Society for Optical Engineering 11447 2020年Narrow-band filters can detect emission and absorption line features from multiple sources in a field of view simultaneously without spectroscopy. However, it is difficult to estimate and subtract the continuum component from sources of different spectral slope, especially when the equivalent width of the target lines is small. For example, Cataclysmic Variables have equivalent widths of hydrogen recombination emission lines of about -10 to -100 angstroms, but many of the ones that have been detected by conventional NB filters so far have a large equivalent width. We have therefore constructed novel narrow-band filters with transmission bands on both sides of the central wavelengths of the Paβ (1.282 µm) and Brγ (2.167 µm) emission lines so that we can evaluate the continuum level more accurately than the conventional filters having transmission in only one side of the target line. We installed the narrow-band filters to the Simultaneous three-color InfraRed Imager for Unbiased Survey (SIRIUS) in the InfraRed Survey Facility (IRSF) telescope at South African Astronomical Observatory (SAAO), and evaluated their performance. We found that the narrow-band filters can detect emission line features with an equivalent width of several tens of angstroms. Thus, this filter set is useful for detecting emission line features from targets with small equivalent widths that have been difficult to detect with the conventional NB filter set.
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Journal of Low Temperature Physics 199(3-4) 1107-1117 2020年Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite cosmic microwave background (CMB) polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA's H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the CMB by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34 and 448 GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy's foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5 K for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun-Earth Lagrangian point, L2, are planned for 3 years. An international collaboration between Japan, the USA, Canada, and Europe is sharing various roles. In May 2019, the Institute of Space and Astronautical Science, JAXA, selected LiteBIRD as the strategic large mission No. 2.
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Journal of Low Temperature Physics 194(5-6) 443-452 2019年3月15日LiteBIRD is a candidate satellite for a strategic large mission of JAXA. With its expected launch in the middle of the 2020s with a H3 rocket, LiteBIRD plans to map the polarization of the cosmic microwave background radiation over the full sky with unprecedented precision. The full success of LiteBIRD is to achieve δr< 0.001 , where δr is the total error on the tensor-to-scalar ratio r. The required angular coverage corresponds to 2 ≤ ℓ≤ 200 , where ℓ is the multipole moment. This allows us to test well-motivated cosmic inflation models. Full-sky surveys for 3 years at a Lagrangian point L2 will be carried out for 15 frequency bands between 34 and 448 GHz with two telescopes to achieve the total sensitivity of 2.5 μ K arcmin with a typical angular resolution of 0.5 ∘ at 150 GHz. Each telescope is equipped with a half-wave plate system for polarization signal modulation and a focal plane filled with polarization-sensitive TES bolometers. A cryogenic system provides a 100 mK base temperature for the focal planes and 2 K and 5 K stages for optical components.
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Monthly Notices of the Royal Astronomical Society 482(4) 5316-5326 2019年2月1日Short X-ray reverberation lags are seen across a broad Fe–K energy band in more than 20 active galactic nuclei (AGNs). This broad iron line feature in the lag spectrum is most significant in super-Eddington sources such as Ark 564 (L/LEdd ∼ 1) and 1H 0707–495 (L/LEdd 10). The observed lag time-scales correspond to very short distances of several Rg/c, so that they have been used to argue for extremely small ‘lamp-post’ coronae close to the event horizon of rapidly spinning black holes. Here, we show for the first time that these Fe–K short lags are more likely to arise from scattering in a highly ionized wind, launched at ∼50 Rg, rotating and outflowing with a typical velocity of 0.2c. We show that this model can simultaneously fit the time-averaged energy spectra and the short-time-scale lag–energy spectra of both 1H 0707–495 and Ark 564. The Fe–K line in 1H 0707–495 has a strong P-Cygni-like profile, which requires that the wind solid angle is large and that our line of sight intercepts the wind. By contrast, the lack of an absorption line in the energy spectrum of Ark 564 requires rather face-on geometry, while the weaker broad Fe–K emission in the energy and lag–energy spectra argue for a smaller solid angle of the wind. This is consistent with theoretical predictions that the winds get stronger when the sources are more super-Eddington, supporting the idea of AGN feedback via radiation-pressure-driven winds.
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Journal of Low Temperature Physics 194(5-6) 443-452 2019年LiteBIRD is a candidate satellite for a strategic large mission of JAXA. With its expected launch in the middle of the 2020s with a H3 rocket, LiteBIRD plans to map the polarization of the cosmic microwave background radiation over the full sky with unprecedented precision. The full success of LiteBIRD is to achieve δr< 0.001 , where δr is the total error on the tensor-to-scalar ratio r. The required angular coverage corresponds to 2 ≤ ℓ≤ 200 , where ℓ is the multipole moment. This allows us to test well-motivated cosmic inflation models. Full-sky surveys for 3 years at a Lagrangian point L2 will be carried out for 15 frequency bands between 34 and 448 GHz with two telescopes to achieve the total sensitivity of 2.5 μ K arcmin with a typical angular resolution of 0.5 ∘ at 150 GHz. Each telescope is equipped with a half-wave plate system for polarization signal modulation and a focal plane filled with polarization-sensitive TES bolometers. A cryogenic system provides a 100 mK base temperature for the focal planes and 2 K and 5 K stages for optical components.
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Monthly Notices of the Royal Astronomical Society 482(4) 5316-5326 2019年Short X-ray reverberation lags are seen across a broad Fe-K energy band in more than 20 active galactic nuclei (AGNs). This broad iron line feature in the lag spectrum is most significant in super-Eddington sources such as Ark 564 (L/L-Edd similar to 1) and 1H 0707-495 (L/L-Edd greater than or similar to 10). The observed lag time-scales correspond to very short distances of several R-g/c, so that they have been used to argue for extremely small 'lamp-post' coronae close to the event horizon of rapidly spinning black holes. Here, we show for the first time that these Fe-K short lags are more likely to arise from scattering in a highly ionized wind, launched at similar to 50 R-g, rotating and outflowing with a typical velocity of 0.2c. We show that this model can simultaneously fit the time-averaged energy spectra and the short-time-scale lag-energy spectra of both 1H 0707-495 and Ark 564. The Fe-K line in 1H 0707-495 has a strong P-Cygni-like profile, which requires that the wind solid angle is large and that our line of sight intercepts the wind. By contrast, the lack of an absorption line in the energy spectrum of Ark 564 requires rather face-on geometry, while the weaker broad Fe-K emission in the energy and lag-energy spectra argue for a smaller solid angle of the wind. This is consistent with theoretical predictions that the winds get stronger when the sources are more super-Eddington, supporting the idea of AGN feedback via radiation-pressure-driven winds.
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Journal of Low Temperature Physics 193(5-6) 991-995 2018年12月1日The X-ray Astronomy Recovery Mission (XARM) is a recovery mission of ASTRO-H/Hitomi, which is expected to be launched in Japanese Fiscal Year of 2020 at the earliest. The Resolve instrument on XARM consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput X-ray mirror assembly with the focal length of 5.6 m. Hitomi was launched into orbit in February 2016 and observed several celestial objects, although the operation of Hitomi was terminated in April 2016. The soft X-ray spectrometer (SXS) on Hitomi demonstrated high-resolution X-ray spectroscopy of ~ 5 eV FWHM in orbit for most of the pixels. The Resolve instrument is planned to mostly be a copy of the Hitomi SXS and soft X-ray telescope designs, though several changes are planned based on the lessons learned from Hitomi. We report a brief summary of the SXS performance and the status of the Resolve instrument.
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Journal of Low Temperature Physics 193(5-6) 1048-1056 2018年12月1日Inflation is the leading theory of the first instant of the universe. Inflation, which postulates that the universe underwent a period of rapid expansion an instant after its birth, provides convincing explanation for cosmological observations. Recent advancements in detector technology have opened opportunities to explore primordial gravitational waves generated by the inflation through “B-mode” (divergent-free) polarization pattern embedded in the cosmic microwave background anisotropies. If detected, these signals would provide strong evidence for inflation, point to the correct model for inflation, and open a window to physics at ultra-high energies. LiteBIRD is a satellite mission with a goal of detecting degree-and-larger-angular-scale B-mode polarization. LiteBIRD will observe at the second Lagrange point with a 400 mm diameter telescope and 2622 detectors. It will survey the entire sky with 15 frequency bands from 40 to 400 GHz to measure and subtract foregrounds. The US LiteBIRD team is proposing to deliver sub-Kelvin instruments that include detectors and readout electronics. A lenslet-coupled sinuous antenna array will cover low-frequency bands (40–235 GHz) with four frequency arrangements of trichroic pixels. An orthomode-transducer-coupled corrugated horn array will cover high-frequency bands (280–402 GHz) with three types of single frequency detectors. The detectors will be made with transition edge sensor (TES) bolometers cooled to a 100 milli-Kelvin base temperature by an adiabatic demagnetization refrigerator. The TES bolometers will be read out using digital frequency multiplexing with Superconducting QUantum Interference Device (SQUID) amplifiers. Up to 78 bolometers will be multiplexed with a single SQUID amplifier. We report on the sub-Kelvin instrument design and ongoing developments for the LiteBIRD mission.
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Journal of Low Temperature Physics 193(5-6) 841-850 2018年12月1日The high-frequency telescope for LiteBIRD is designed with refractive and reflective optics. In order to improve sensitivity, this paper suggests the new optical configurations of the HFT which have approximately 7 times larger focal planes than that of the original design. The sensitivities of both the designs are compared, and the requirement of anti-reflection (AR) coating on the lens for the refractive option is derived. We also present the simulation result of a sub-wavelength AR structure on both surfaces of silicon, which shows a band-averaged reflection of 1.1–3.2% at 101–448 GHz.
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Publications of the Astronomical Society of Japan 70(6) 2018年12月1日We present the results from the Hitomi Soft Gamma-ray Detector (SGD) observation of the Crab nebula. The main part of SGD is a Compton camera, which in addition to being a spectrometer, is capable of measuring polarization of gamma-ray photons. The Crab nebula is one of the brightest X-ray/gamma-ray sources on the sky, and the only source from which polarized X-ray photons have been detected. SGD observed the Crab nebula during the initial test observation phase of Hitomi. We performed data analysis of the SGD observation, SGD background estimation, and SGD Monte Carlo simulations and successfully detected polarized gamma-ray emission from the Crab nebula with only about 5 ks exposure time. The obtained polarization fraction of the phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1%±10.6%), and the polarization angle is 110°.7 + 13°.2/-13°.0 in the energy range of 60.160 keV (the errors correspond to the 1 σ deviation). The confidence level of the polarization detection was 99.3%. The polarization angle measured by SGD is about one sigma deviation with the projected spin axis of the pulsar, 124°.0 ± 0°.0.1.
MISC
26共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2019年4月 - 2022年3月
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日本学術振興会 科学研究費助成事業 2018年4月 - 2022年3月
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日本学術振興会 科学研究費助成事業 2016年4月 - 2019年3月
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日本学術振興会 科学研究費助成事業 2015年4月 - 2018年3月
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日本学術振興会 科学研究費助成事業 2012年6月 - 2017年3月
