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 宇宙物理学研究系東京大学 大学院理学系研究科 天文学専攻
- J-GLOBAL ID
- 200901049964309113
- researchmap会員ID
- 5000001980
- 外部リンク
研究キーワード
5経歴
1-
2017年10月 - 現在
主要な論文
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Journal of Astronomical Telescopes, Instruments, and Systems 9(02) 2023年4月19日
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Journal of Astronomical Telescopes, Instruments, and Systems 9(02) 2023年4月12日
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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 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 $2.2\, \mu$K-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.
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Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave 2022年8月27日
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Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave 2022年8月27日
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SPACE TELESCOPES AND INSTRUMENTATION 2022: OPTICAL, INFRARED, AND MILLIMETER WAVE 12180 2022年LiteBIRD is a JAXA-led international project that aims to test representative inflationary models by performing an all-sky cosmic microwave background radiation (CMB) polarization survey for 3 years at the Sun-Earth Lagrangian point L2. We aim to launch LiteBIRD in the late 2020s. The payload module (PLM) is mainly composed of the Low-Frequency Telescope (LFT), the Mid-Frequency Telescope and High-Frequency Telescope (MHFT), and a cryo-structure. To conduct the high-precision and high-sensitivity CMB observations, it is required to cool the telescopes down to less than 5 K and the detectors down to 100 mK. The high temperature stability is also an important design factor. It is essential to design and analyze the cryogenic thermal system for PLM. In this study, the heat balance, temperature distribution, and temperature stability of the PLM for the baseline design are evaluated by developing the transient thermal model. The effect of the Joule-Thomson (JT) coolers cold tip temperature variation, the periodical changes in subK Adiabatic Demagnetization Refrigerator (ADR) heat dissipation, and the satellite spin that generates the variable direction of solar flux incident are implemented in the model. The effect of contact thermal conductance in the LFT and the emissivity of the V-groove on the temperature distribution and heat balance are investigated. Based on the thermal analysis, it was confirmed that the PLM baseline design meets the requirement of the temperature and the cooling capability of the 4K-JT cooler. In addition, the temperatures of the V-groove and the LFT 5-K frame are sufficiently stable for the observation. The temperature stability of the Low Frequency Focal Plane (LF-FP) is also discussed in this paper.
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Proceedings of SPIE - The International Society for Optical Engineering 11453 2020年© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. 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 11453 2020年© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. We are developing a 100-GHz band 109-pixel MKID camera for the Nobeyama 45-m telescope. The camera optics contains plano-convex silicon (Si) lenses with 300-and 154-mm diameters located at the 4-K and 1-K stages, and a vacuum window of 320-mm diameter. Antireflective subwavelength structures (SWSs) for the Si lenses and the vacuum window were designed to reduce surface reflection. Cyclo olefin polymer (COP) was chosen as the base material for vacuum window as the dielectric loss is comparable with high-density polyethylene and it is easy to fabricate. Antireflective SWSs optimized for 100-GHz band were simulated using ANSYS HFSS. A one-layer rectangular pillar was designed for a Si lens of 300-mm diameter and a 320-mm diameter COP window to examine the fabrication process in large areas. For 154-mm diameter Si lens, a 1.2-mm depth tapered structure was used to obtain broadband characteristics. These designed structures were fabricated on both sides using a three-Axis numerically-controlled machine. An end mill and a metal-bonded dicing blade were used for cutting the COP and Si, respectively. W-band vector network analyzer was used for S-parameter measurements of the SWS formed flat surface at an ambient temperature. Average surface reflectance of Si lenses and transmittance of the COP window in the 90-110 GHz range were found at approximately 1% and 98%, respectively.
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IEEE Transactions on Terahertz Science and Technology 9(6) 598-605 2019年11月 査読有り© 2019 IEEE. Polarization of the cosmic microwave background (CMB) has crucial information on the inflationary universe. To detect these signals, it is necessary to suppress far sidelobes of a telescope, which contaminate the CMB signals with strong foreground radiation, such as the Galactic plane. LiteBIRD is the only funded CMB observation satellite for the 2020s, and the low frequency telescope (LFT; 34-161 GHz) is one of its telescopes. We measured near-field antenna patterns of the LFT using its 1/4-scaled model and examined far sidelobes up to 60° from the peaks. To cover the 20° field of view of the LFT, we investigated the antenna patterns at the edges of the focal plane as well as at the center. The measurement frequencies were 140-220 GHz, which correspond to the lowest bands (35-55 GHz) of the full-scale LFT. The measurements were consistent with the simulated far-sidelobe patterns at least -50 dB level, and showed that far sidelobes for two orthogonal polarization directions are consistent with each other down to -40 dB level. We also measured the cross-polarization patterns, and their peak level was less than -20 dB.
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Journal of Astronomical Telescopes, Instruments, and Systems 5(4) 2019年10月1日 査読有り© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE). Radiative cooling with thermal isolation shields can provide a reliable cooling system for instruments onboard satellites in orbit. We report the optimization study for the cryogenic architecture of the LiteBIRD satellite using radiative cooling. A trade study that changed the number of thermal shields and shield emissivity were conducted. The heat flow from 300 to 4.5 K, including active cooling by mechanical cryocoolers, was evaluated among the trade designs. We found that the design that consists of low-emissivity four-layer thermal shields is optimum in terms of thermal performance and system design. The optimum design achieved a heat load of 29.9 mW for the 4.5-K cooling stage, whereas the requirement was 30 mW with the assumed cryogenic system.
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Proceedings of SPIE - The International Society for Optical Engineering 10698 2018年 査読有り© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. LiteBIRD is a candidate for JAXA's strategic large mission to observe the cosmic microwave background (CMB) polarization over the full sky at large angular scales. It is planned to be launched in the 2020s with an H3 launch vehicle for three years of observations at a Sun-Earth Lagrangian point (L2). The concept design has been studied by researchers from Japan, U.S., Canada and Europe during the ISAS Phase-A1. Large scale measurements of the CMB B-mode polarization are known as the best probe to detect primordial gravitational waves. The goal of LiteBIRD is to measure the tensor-to-scalar ratio (r) with precision of r < 0:001. A 3-year full sky survey will be carried out with a low frequency (34 - 161 GHz) telescope (LFT) and a high frequency (89 - 448 GHz) telescope (HFT), which achieve a sensitivity of 2.5 μK-arcmin with an angular resolution 30 arcminutes around 100 GHz. The concept design of LiteBIRD system, payload module (PLM), cryo-structure, LFT and verification plan is described in this paper.
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IEEE Transactions on Applied Superconductivity 25(3) 2015年6月1日 査読有り© 2002-2011 IEEE. We developed SIS mixers for Atacama large millimeter/submillimeter array (ALMA) Band 8 (385-500 GHz) receiver cartridges and evaluated their performance. DC IV curves of the SIS mixers showed small leakage current at the high current density. The current density and quality factor (R-{sg}/R-{n}) of the Band 8 SIS junction were 13 \hbox{kA/cm}{2} and approximately 20, respectively. Double-sideband noise temperature of the 266 SIS mixers was 92.8 K at 4.0 K bath temperature on the average from 385 to 500 GHz with a standard deviation of 7.0%. A couple of sideband-separating (2SB) mixers for dual polarizations were used in the Band 8 receiver cartridge. The 73 receivers have met ALMA specifications of the noise temperature. Single-sideband noise temperature and image rejection ratio of the receivers were 139.5 K and 20.5 dB on the average from 385 to 500 GHz, respectively. These test results of the receivers indicate high quality and uniformity of the 2SB mixers.
MISC
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Journal of Molecular Spectroscopy 185(1) 21-25 1997年9月 査読有りThe rotational spectral lines of the 13C isotopic species of CCS (13CCS, C13CS, and 13C13CS) have been observed using a Fourier transform microwave spectrometer in combination with a pulsed-discharge nozzle. The hyperfine-resolved JN = 10-01, JN = 21-10, and JN = 32-21 transitions have been observed in the 11-, 22-, and 33-GHz regions, respectively, with an accuracy of about 5 kHz. The observed transition frequencies for 13CCS and C13CS are analyzed simultaneously with millimeter-wave data, and the hyperfine interaction constants for both species are determined accurately. Astronomical implications for these radicals are discussed. © 1997 Academic Press.
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ASTROPHYSICAL JOURNAL 481(2) 821-831 1997年6月 査読有りHard X-ray and gamma-ray emissions from the Galactic ridge were studied with the large area proportional counter (LAC) on the Ginga satellite and a balloon-borne detector Welcome-1. In the scanning observations with the LAC, diffuse hard X-rays were detected along the Galactic plane between l = -20 degrees and l = 40 degrees. The measured spectrum shows that a hard component exists in the Galactic ridge emission above 10 keV, in addition to the hot plasma component. The estimated luminosity of the Galactic ridge emission is around 2 x 10(38) ergs s(-1) in the 3-16 keV band. Welcome-1 observed the gamma-ray ridge emission at around l similar to 345 degrees between 50 and 600 keV. These two results and a recent COMPTEL study suggest that the spectrum of the diffuse Galactic ridge emission extends over the keV-MeV range. From the observed spectral slope, bremsstrahlung by electrons is shown to be the dominant emission mechanism. This implies that low-energy electrons must be supplied continuously to sustain emission in the hard X-ray band. We propose a scenario in which the thermal electrons in the hot plasma responsible for the strong Fe K X-ray emission are shock-accelerated continuously in supernova remnants (SNRs), producing the observed hard X-ray and gamma-ray emissions from the Galactic ridge.
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Astrophysical Journal 489(1 PART II) 1997年 査読有りWe report CO (J = 2-1, J = 1-0) outflows from four X-ray-emitting protostars (EL29, IRS44, WL6, WL10) in the p Ophiuchi cloud core which have been firmly identified with the X-ray satellite ASCA. The common feature of these outflows is that the blue and red lobes are largely overlapped, which indicates that the inclination angle between the outflow axis and line of sight is smaller than 30° (nearly pole-on configuration). Taking account of the hard X-ray transparency (NH ∼ 1023 cm-2) and the column density of a circumstellar disk (NH > 1024 cm-2), it is naturally understood that hard X-rays emitted near the surface of protostars or the inner part of the disk are observed in the nearly pole-on configuration. The outflow detection rate (4/5) in the present observations shows that a low-mass protostar emits X-rays even in the outflow phase of early stellar evolution. © 1997. The American Astronomical Society. All rights reserved.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 48(6) 801-811 1996年12月We have studied Cen A (NGC 5128) in the X-ray band (3-20 keV) and soft gamma-ray band (40-600 keV) with the Large Area Counter (LAG) of the Ginga sattellite (1989 March and 1990 February) and with a balloon-borne low background detector (Welcome-1, 1991 November), respectively. The observed continuous spectra show a power-law shape (r similar to 1.8) with relatively heavy absorption (N-H similar to 1.5 x 10(23)H cm(-2)) at the low-energy end and a possible break at similar to 180 keV. We analyzed the total spectra as the sum of the direct power-law flux from the central engine, the Compton-scattered flux from a cold cloud near to the engine, and the iron fluorescence-line flux. By assuming that the geometry around the central engine remained unchanged during the two-year period, we studied two possible cold cloud geometries by comparing Monte-Carlo simulations with our observations: the first is the Compton-reflection model in which the cloud forms a slab covering 2 pi sr behind the central engine, the second is a case where the central source is totally surrounded by a cold cloud. We found that the latter geometry reproduces our data well; the observed power-law spectrum is then identified as direct flux from the central engine which undergoes a break at similar to 180 keV.
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International Journal of Infrared and Millimeter Waves 17(7) 1263-1284 1996年 査読有りWe measured atmospheric opacity at 220 GHz at the summit of Mt. Fuji (alt. 3776 m) about one year in order to explore a feasibility of submillimeter-wave astronomical observations. For this purpose, a 220 GHz radiometer system enclosed in a radome (51 × 51 × 62 cm3) has been developed. The 220 GHz opacity was lower than 0.06 for a significant fraction (∼ 45%) of time from November 1994 to March 1995. Diurnal variation of the opacity at the summit of Mt. Fuji is so small that continuous observation at submillimeter-wave is possible through day and night. Yearly variation of the opacity is studied from water vapor pressure data measured at the weather station for the past 3 years. To prevent accumulation of ice and snow on the Gore-Tex membrane in the radome, the outer membrane was supplied with a thermal flux of 0.63 kW m-2 and the adjacent metal radome surfaces were supplied with a flux of ∼0.9 kW m-2. We evaluate from the 220 GHz transmission data that this heat flux is sufficient to keep the membrane on the radome free of ice and snow during 83% of the time in 5 winter months. The summit of Mt. Fuji appears to be a promising site for submillimeter-wave observations. © 1996 Plenum Publishing Corporation.
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Publications of the Astronomical Society of Japan 48(2) 171-189 1996年 査読有りThe in-orbit performance and calibration of the Gas Imaging Spectrometer (GIS), located on the focal plane of the X-ray astronomy satellite ASCA, are described. An extensive in-orbit calibration has confirmed its basic performance, including a position resolution of 0.6 mm (FWHM) and an energy resolution of 7.8% (FWHM), both at 6 keV. When combined with the X-ray telescope, the GIS sensitivity range becomes 0.7-10 keV. The in-orbit non X-ray background of the GIS has been confirmed to be as low as (5-9) × 10-4 c s-1 cm-2 keV-1 over the 1-10 keV range. The long-term detector gain has been stable within a few % for nearly 3 years. Extensive observations of the Crab Nebula and other sources have provided accurate calibrations of the position response, photometric capability, dead time, and timing accuracy of the GIS. Furthermore, the overall energy response, including the temporal and positional gain variations and the absolute gain scale, has been calibrated to ∼ 1%. Thus, the GIS is working as an all-round cosmic X-ray detector, capable of X-ray imagery, fine X-ray spectroscopy, X-ray photometry with a flux dynamic range covering more than 5 orders of magnitude, and fast X-ray photometry with a time resolution up to 60 μs.
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Journal of Molecular Spectroscopy 174(1) 196-204 1995年11月 査読有りThe rotational spectral lines of the linear C5D radical in the 2Π electric ground state are observed with a source-modulation microwave spectrometer and a Fourier-transform microwave spectrometer. Forty-eight spectral lines in the 173-279 GHz region and 10 in the 11-16 GHz region are measured and 10 molecular constants, including hyperfine interaction constants, are determined by a least-squares method. Frequencies of low-J rotational transitions of C5D are calculated for radio astronomical observations. © 1995 Academic Press, Inc.
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Astrophysical Journal 443(1) 271-273 1995年4月 査読有りTwo pulsed X-ray profiles of the Crab pulsar taken at a 4.5 yr interval have been compared to study possible long-term variabilities in its pulse intensity and pulse profile. The intensity ratio of the second peak to the first peak remained constant within 2.7% in our study in the X-ray band, while the ratio has been reported to have varied by a factor around 3 over the same interval in the γ-ray band. Our results give constraints on possible origins of the reported variation in the γ-ray band for the Crab pulsar. The results also set a limit on possible change in its pulsed X-ray emission after the 1989 glitch.
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Astrophysical Journal 443(2) 780-785 1995年4月 査読有りBased on recent studies of soft γ-rays from PSR B1509-58, stability of the X-ray pulse from the Crab pulsar, and the interpulse emission from the Crab pulsar, a unified picture for high-energy emission in spin-powered pulsars is proposed. The picture assumes that pulsed X-rays and γ-rays are emitted both from the polar cap and outer gap regions. We then note that the luminosity and characteristic energy of emitted X-rays and γ-rays are expected to scale differently to the pulsar parameters, because the relevant physics processes are different in the two regions. We assume two baseline emissions, the Crab broad interpulse emission for the polar cap region and the Vela double peak emission for the outer gap region, and we scale them to predict high-energy emissions from other pulsars. The luminosity and energy range of the predicted pulsed emissions agree reasonably well with observations for PSR B1509-58: the observed broad X-ray/soft γ-ray emission comes from the polar cap region, while the double peak emission expected from the outer gap region is probably too faint for EGRET to observe. A broad polar cap emission is predicted for the Vela pulsar in the MeV range at a luminosity between the Crab interpulse and the broad PSR B1509-58 pulse.
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Proceedings of SPIE - The International Society for Optical Engineering 2518 85-95 1995年 査読有りThe ASTRO-E satellite is scheduled for launch in 2000 by the Institute of Space and Astronautical Science (ISAS). In this paper the design and performance of the hard x ray detector (HXD) developed for ASTRO-E are described. The HXD is a combination of YAP/BGO phoswich scintillators and silicon PIN diodes covering a wide energy band of 10 - 700 keV. The detector background is reduced down to several times 10 -6c/s/cm 2/keV, and the sensitivity of the HXD is more than one order of magnitude higher than any other past missions in the range of a few 10 keV to several 100 keV. Thus ASTRO-E HXD is expected to achieve an extreme high performance for detecting cosmic hard x rays and low-energy gamma rays. Astrophysics to be explored with the HXT are expected to be extremely widespread and rich.
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Proceedings of SPIE - The International Society for Optical Engineering 2518 2-12 1995年 査読有りThe fourth Japanese x-ray astronomy satellite, ASCA, carries two imaging gas scintillation proportional counters (GIS) on its focal plane. Extensive ground calibration has established its position resolution to be 0.5 mm and FWHM energy resolution to be 8.0% both at 6 keV. When combined with the x-ray telescope, a sensitivity range becomes 0.7 - 10 keV. These properties have been confirmed through in-orbit calibrations. The in-orbit background of the GIS has been confirmed to be as low as (5 - 7) × 10 -4 c s -1cm -2keV -1 over the 1 - 10 keV range. The long-term detector gain is stable within a few % for two years. Gain dependence on the position and temperature has been calibrated down to 1%. The overall energy response is calibrated very accurately. Thus the GIS is working as an all-round cosmic x-ray detector.
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Astrophysical Journal 428(1) 284-291 1994年6月10日 査読有りWe observed a young rotation-powered pulsar, PSR 1509-58, in the hard X-ray/y-ray or the soft γ-ray band with a balloon-borne detector in Brazil on 1991 November 19 (UT). With a timing analysis we detected pulsations in the energy band 94-240 keV at the 150.687 ms period determined from radio observations. The pulsating flux is (7.1 ± 1.7) × 10 -4 cm -2 s -1 in this band, and the energy spectrum follows a power law with photon index α = 1.64 ± 0.4. The averaged pulse profile shows a broad single peak with a sharp rise and has a duty cycle around 50% or higher: these features are similar to what have been observed in the X-ray band by the Ginga satellite. Based on the data available now, the fraction of energy transformed from rotational energy loss to pulsed/ nonpulsed soft γ-ray radiation is estimated. If the solid angle swept by the pulsed beam is about the same as for the Crab pulsar (PSR 0531+21) and the Vela pulsar (PSR 0833-45), PSR 1509-58 turn out to be an extremely efficient pulsar, converting a large fraction of its rotational energy loss to radiation, as the outer gap model predicts. The observed pulsed spectrum, however, is strong in the soft γ-ray band, in a sharp contrast to what has been observed in the Vela pulsar, a pulsar expected to be similar PSR 1509-58 in the outer gap model. The fact that the pulse profile remains broad and single-peaked in the soft γ-ray band is also new for Crab-like pulsars. In these regards, PSR 1509-58 may require some alteration to the standard outer gap model or even a new model for gamma-ray emission in pulsars.
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IEEE Transactions on Nuclear Science 40(4) 890-898 1993年8月 査読有りWe have developed a low background hard X-ray/gamma-ray telescope (Welcome-1) for balloon-borne experiments in the energy range from 40 keV to 800–1000 keV. The detector is based on newly developed well-type phoswich counters. In the first well-type phoswich counter, GSO(Ce) (Gd<inf>2</inf>SiO<inf>5</inf> doped with Ce) is used as the detection part and CsI(T1) as the shielding part. Welcome-1 consists of 64 GSO/CsI well-type phoswich counters assembled in the “compound-eye” configuration and the effective area is 740 cm2 at 122 keV and 222 cm2 at 511 keV line. The well-type phoswich counter and the compound eye configuration reduces background significantly both external and internal and allows us a high signal-to-noise ratio in balloon-borne experiments. The data from the detector is taken by the versatile data acquisition system based on the VME computer specially designed for balloon-borne experiments. In the system, the arrival time of each event is recorded by the clock system which utilizes GPS satellite. The background levels at an altitude of 4.5g/cm2 are 1×10-4/cm2/s/keV at 122 keV. Crab nebula has been observed with the signal to background ratio better than unity between 100 and 200 keV. In this paper, the desine of the telescope and the flight performace are presented. © 1993 IEEE
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IEEE Transactions on Nuclear Science 40(2) 204-207 1993年4月 査読有りWe have developed a new kind of phoswich counters that are capable of detecting low flux hard X-ray / γ-ray from localized sources. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The well-shaped shielding part acts as an active collimator as well as an active shield. The whole assembly is viewed by a phototube from the exterior bottom surface of the shielding part. By using an appropriate pulse-shape discriminator (PSD), hard X-rays/gamma-rays that have deposited energy only in the detection part can be selected. The first model counter was built by using a new scintillator (GSO) in the detection part and Csl(Tl) in the shielding part. A detector system consisting of 64 such phoswich counters (total area ~ 740 cm<sup>2</sup>) was flown on board a baloon, setting a limit to the <sup>57</sup>Co line flux from SN1987A at around 10<sup>-4</sup> cm<sup>-2</sup> s. The sensitivity for continuum flux was around a few X l0<sup>-6</sup> cm<sup>-2</sup> s<sup>-1</sup> keV<sup>-1</sup> between 100 and 200 keV. Efforts to lower the sensitivity further are under-way. In the second model, Csl(Tl) was replaced by BGO and radioactive contaminations in GSO were reduced. More improvements are to be made the in near future to reach a sensitivity (3σ) around 5 X 10<sup>-7</sup> cm<sup>-2</sup> s<sup>-1</sup> keV<sup>-1</sup> for continuum. © 1993 IEEE
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COMPTON GAMMA-RAY OBSERVATORY 280 355-359 1993年 査読有り© 1993 American Institute of Physics. The black hole candidate GX339-4 and the Galactic Center region were observed simultaneously in the hard X-ray region with the balloon-borne telescope, Welcome-1. The obtained energy spectrum of GX339-4 is harder than that of the Galactic Center and is consistent with a single power-law function of photon index α=1.52±0.34 in the energy range 60-600 keV.
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AIP Conference Proceedings 280 213-217 1993年 査読有り© 1993 American Institute of Physics. The energy spectra and the pulse light curve of PSR1509-58 in the X-ray range 2 - 60 keV are presented. The X-ray pulse spectrum can be fitted by a power-law model with a photon index of ∼ 1.3. The non-pulse component is softer, and has a photon index of 2.2 if modeled by a power-law. The Crab pulsar was observed by Ginga in March 1987 and September 1991. The variation of single pulse intensity was evaluated with a best statistics in the 2 - 11 keV X-ray, but no significant deviation from the Poisson fluctuation was found. The longterm variation of the relative intensity of the two peaks in the pulse profile was studied using the data taken 4.5 years apart. Unlike in the gamma-ray range, no significant variation of the pulse peaks were found. In this respect the soft X-ray pulse in the Crab pulsar shares more characteristics in common with the optical pulse rather than the gamma-ray.
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AIP Conference Proceedings 280 523-527 1993年 査読有り© 1993 American Institute of Physics. We studied hard X-ray/γ-ray emission from Cen A (NGC 5128) in a balloon experiment with a low background detector (Welcome-1) in Brazil. The energy spectrum of CenA is obtained from 40 keV to 600 keV. We combined the energy spectrum obtained by the Ginga satellite in a similar state. The combined spectrum indicates that there is a break at 185 ± 22 keV. The spectrum is fitted to the broken power law model with the photon index of α 1 =-1.79 up to 188 keV, and α 2 =-3.7 -1.7+0.9 above the break.
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IEEE Transactions on Nuclear Science 39(5) 1316-1320 1992年10月 査読有りWe have developed a simple pulse shape discriminator (PSD) for applications where a large number of channels are used within limited space and electric power. In the PSD, the output signal from a photomultiplier is differentiated and integrated to form a triple-polar pulse. The time interval between the first and second zero crossings depends on the decay time of the scintillation light. The circuit selects signals from the proper scintillator by using this interval. By this method, we can significantly reduce the effect of time slewing in the low energy region. We have successfully operated sixty four channels of the PSD in a balloon borne hard X-ray experiment. © 1992 IEEE
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Astrophysical Journal 397(2 PART 2) L83-L86 1992年10月1日 査読有りWe studied the γ-ray flux from SN 1987A with a balloon-borne detector in Brazil on 1990 November 29. By comparing on- and off-source data, we obtained limits to the total γ-ray flux due to 57Co decays and presumed pulsar activity. If the pulsar contribution is neglected, an upper limit (90% confidence limit) is set to the total 57Co contribution above 60 keV at 2.7 × 10-4 cm-2 s-1 where the 122 keV line contribution is 1.0 × 10-4 cm-2 s-1. The corresponding limit on the abundance ratio of 57Co and 56Co is 3.4 times that of the Sun. The present upper limit implies that the reported leveling off in the light curve of SN 1987A is primarily due to the pulsar activity. If the pulsar is Crab-like (photon index -2.2), the light curve requires an energy outflow greater than 0.95 × 1037 ergs s-1 (above 1 keV) now being supplied to SN 1987A by its presumed pulsar.
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宇宙科学研究所報告. 特集 30 61-81 1992年2月We have developed a new kind of phoswih counters (the well-type phoswich counter) that is capable of detecting very low flux hard X-rays/gamma-rays (60-800 keV) from astronomical object. We flew the first prototype detector system (Welcome-1) from Cachoeira Paulista, Brazil in November 1990. The objective was to detect ^<57>Co (122,136keV) and continuum emission from SN1987A. The background spectrum taken at an altitude of 4g/cm^2 indicates that the 3σ sensitivity reaches ∿a few×10^<-6>/cm^2/s/keV and ∿10^<-4>/cm^2/s by 10^4s observation for the continuum spectrum and line spectrum respectively.
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Proceedings of SPIE - The International Society for Optical Engineering 1734 44-55 1992年 査読有りWe have developed a low background hard x-ray/γ-ray telescope for balloon-borne experiments. The telescope called Welcome-1 (well type compound eye) utilizes newly developed well-type phoswich counters. In the well-type phoswich counter, the background from external and internal (nuclear activation) sources are reduced significantly. Welcome-1 is designed for observation in the energy range from 60 keV to 800 - 1000 keV. The effective area of Welcome-1 is 740 cm2 at 122 keV and 222 cm2 at 511 keV line. We flew Welcome-1 from Cachoeira Paulista, Brazil in 1990 and 1991 to detect hard x rays from SN1987A, PSR1509-58, Cen-A, and others. The background levels at an altitude of 4 g/cm2 are 1 × 10-4/cm2/s/keV at 122 keV and 4 × 10-5/cm2/s/keV at 511 keV. The data obtained during the flight shows that the detector in fact has the 3σ sensitivity of approximately a few × 10-6/cm2/s/keV and approximately 10-4/cm2/s in a 104s observation for the continuum spectrum and line spectrum, respectively. Crab nebula has been observed with S/N ratio better than unity between 100 and 200 keV.
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Proceedings of SPIE - The International Society for Optical Engineering 1734 2-13 1992年 査読有りWe have developed a new kind of phoswich counters that are capable of detecting low flux hard x ray/γ ray from localized sources. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The well-shaped shielding part acts as an active collimator as well as an active shield. The whole assembly is viewed by a phototube from the exterior bottom surface of the shielding part. By using an appropriate pulse-shape discriminator (PSD), hard x rays/γ rays that have deposited energy only in the detection part can be selected. The first counter was built by using a new scintillator (GSO) for the detection part and CsI(Tℓ) for the shielding part. A detector system consisting of 64 such phoswich counters (total area approximately 740 cm2) was flown three times on board a balloon, setting a limit to the 57Co line flux from SN1987A at around 10-4 cm-2s, determining the pulsating hard x/γ ray flux of PSR1509-58, determining the hard x/γ ray spectra of CenA and GX339-04. Analyses have revealed the fact that background counts due to the Compton scattering, nuclear reactions, and β-γ radioactivities in the detector are largely suppressed because they are likely to register at least one extra count in the shielding part. The ultimate sensitivity of the detector is then determined by the level of radioactive contamination. Other scintillator combinations such as GSO/BGO, NaI(Tℓ)/CsI(Tℓ), and YAlO3/BGO also have been studied. Efforts to reduce the radioactive contamination in scintillators also have been actively pursued. In the near future we expect to reach a sensitivity (3σ) around a few times 10-7 cm-2s-1keV-1 for continuum in a
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SCIENTIFIC BALLOONING 13 165-168 1992年We have developed a new kind of phoswich counters that will be capable of detecting low flux hard X-rays/gamma-rays from astronomical objects. The new phoswich counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a rectangular well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). Here, the well-shaped shielding part acts as an active collimator as well as an active shield. We have built a detector system consisting of 64 such phoswich counters: newly developed scintillator (GSO) is used for the detection part and CsI(Tl) is used for the shielding part. The total geometrical area of the 64 detection parts is about 740cm 2 and its 3σ sensitivity is expected to reach below 10 -5 cm -2 s -1 keV -1 up to 700keV. With several improvements such detectors will be able to detect hard X-rays/gamma-rays at a flux level around 10 -6 cm -2 s -1 keV -1 upto 2 MeV. © 1992.
講演・口頭発表等
78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 2023年6月 - 2027年3月
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1● 指導学生等の数
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年度2021年度(FY2021)博士課程学生数1修士課程学生数1インターンの人数9
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指導学生名高倉隼人所属大学東京大学受賞内容（タイトル、団体名等）B-mode from space受賞年月日2019-12-5
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専任大学名東京大学（University of Tokyo)
