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 教授東京大学大学院 理学系研究科 物理学専攻 教授量子場計測システム国際拠点(QUP) (主任研究者)北里大学大学院 理学研究科 客員教授
- 学位
- 博士（理学）(1996年3月 東京大学)
- ORCID ID
https://orcid.org/0000-0003-4885-5537- J-GLOBAL ID
- 200901003330670433
- Researcher ID
- C-2252-2008
- researchmap会員ID
- 5000019022
- 外部リンク
経歴
2-
2002年7月 - 2018年1月
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1993年 - 2002年
学歴
2-
1989年4月 - 1993年3月
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1985年4月 - 1989年3月
委員歴
2-
2017年10月 - 2023年9月
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2014年10月 - 2017年9月
論文
257-
Proceedings of SPIE - The International Society for Optical Engineering 5168 364-375 2004年X-Ray Spectrometer (XRS) is the microcalorimeter onboard the X-ray astronomy satellite Astro-E2 which is scheduled to be launched early in 2005. For the XRS to achieve its best energy resolution of 6 eV at 6 keV, X-ray intensity should be limited up to several c s-1 pixel-1. The filter wheel (FW) is the instrument to reduce incident X-ray intensity on the XRS using extinction filters. The FW consists of a stepping motor, extinction filters, and a filter disk which has six mounting positions for the extinction filters. Among the six mounting points, two are used for Neutral Density (ND) filters, another two are for Beryllium (Be) filters, and the other two are remained open. The biggest modification from Astro-E is that we attach radioisotopes of 55Fe and 41Ca on the filter disk, which illuminate the XRS pixels to monitor the gain in orbit. We present here the mechanical design of the FW especially on improvements from Astro-E, and the results of our calibration measurements on X-ray transmission of the extinction filters.
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SENSORS AND ACTUATORS A-PHYSICAL 114(2-3) 2004年 査読有り
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 523(1-2) 2004年 査読有り
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Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 43(3) 1190-1195 2004年 査読有りAn X-ray microcalorimeter is a cryogenic energy-dispersive spectrometer, which has an energy resolution almost comparable to that of conventional wavelength-dispersive spectrometers. Using a transition edge sensor (TES) as a temperature sensor, the energy resolution can be further improved. We have developed a new method of achieving an array of TES microcalorimeters for the purpose of X-ray imaging. To achieve this, mushroom-shaped X-ray microabsorbers formed using electrodeposition were applied. The temperature of the TES, which is easily degraded by thermal diffusion, was kept sufficiently low throughout the process to achieve practical use. On the bases of this new method, a 2 × 2 (× 4) array of TES microcalorimeters was fabricated and tested. A high energy resolution of 13.0 eV at 6 keV was achieved and the filling factor was improved to 83%. Although several issues still need to be investigated, we verified that our method is useful for fabricating a Ti-Au TES microcalorimeter array.
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Advances in Space Research 34(12) 2530-2534 2004年 査読有りWe report on the results of Chandra observations of the galaxy cluster AWM7. The ACIS image reveals new substructures with a spatial extent of more than 8″ (4 kpc at AWM7) near the cD galaxy center, represented by a hard sub-peak and a soft peak. These substructures suggest that a dynamical process related to the formation of the cD galaxy is now taking place. Inside the cluster core within a radius of 2′, annular spectra with every 10″ step are fitted well by single temperature models. The temperature gradually drops from 4.2 keV at a radius of 60 kpc (2′) to 1.8 keV at the cluster center. The radial abundance profile shows a gradient with a peak metallicity of 1.5 solar at a radius of about 15″ (7 kpc). A two-dimensional map shows two high metallicity blob-like regions, which may be the gas expelled from the cD galaxy. © 2004 Published by Elsevier Ltd on behalf of COSPAR.
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Publications of the Astronomical Society of Japan 56(3) 453-464 2004年 査読有りWe report on ASCA observations of the two nearby globular clusters, M 4 and NGC 6397. Although 14 and 8 sources were detected at more than the 5 σ confidence level from each cluster field, respectively, the majority of them, except for the cores of both clusters, were found unlikely to be associated with the clusters. The core of NGC 6397 shows optically thin thermal plasma emission with a temperature of kT ≳ 12 keV. This result supports the results of HST, ROSAT, and Chandra, indicating that the main constituent of the NGC 6397 core is cataclysmic variables (CVs). The high temperature suggests it to be magnetic CVs, which supports the result of the HST spectroscopy. The core of M 4 was unambiguously detected at a ≳ 5 σ confidence level for the first time. Although we cannot carry out a detailed spectral analysis on the M 4 core due to a statistical limitation, the hardness ratio of the detected photons is also consistent with CVs. We compared the ASCA fluxes of the core sources to those from other X-ray observations. The absorption-corrected 0.5-10 keV flux of the NGC 6397 core with ASCA was obtained to be 2.5 × 10-12erg cm-2 s-1, and had been constant within a factor of ∼ 2 during 1993-2001. The M 4 core flux obtained under the same condition is 2.6 × 10-13 erg cm-2 s-1, which seems to be ∼ 4 times as high as the ROSAT HRI flux, although the possibility of a constant flux between the ASCA and HRI observations cannot be excluded due to a statistical limitation. Spectral and temporal properties of other out-of-core sources, including the radio galaxy PKS 1620-260 and the G0V star V972 Sco, are also described.
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Publications of the Astronomical Society of Japan 56(5) 743-752 2004年 査読有りA Chandra observation of the non-cooling flow cluster A 1060 has confirmed that the hot intracluster medium has fairly uniform distributions of temperature and metal abundance from a radius of about 230 kpc to the central 5 kpc region (H0 = 75 kms-1 Mpc-1). The radial temperature profile shows a broad peak at 30-40 kpc from the center at a level ∼ 20% higher than that in the outer region. Assuming spatially uniform temperature and abundance distributions, we derived a 3-dimensional density structure by iteratively correcting the β model, and obtained the central gas density to be 8.21.0 +1.8 × 10 -3cm-3. The distribution of gravitational mass was estimated from the density profile, and a central concentration of mass within a radius of 50 kpc was indicated. The data also suggest several high-abundance regions. The most significant blob adjacent to the central galaxy NGC 3311 has a radius of about 9 kpc, which indicates a metallicity of ∼ 1.5 solar. We consider that this blob may be produced by the gas stripped off from NGC 3311.
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Publications of the Astronomical Society of Japan 56(6) 939-957 2004年 査読有りWe present an analysis of mock spectral observations of warm-hot intergalactic medium (WHIM) using a constrained simulation of the local universe. The simulated map of oxygen emission lines from local WHIM well reproduces the observed structures traced by galaxies in the real local universe. We further attempt to perform mock observation of the outer parts of the simulated Coma cluster and A 3627 adopting the expected performance of DIOS (Diffuse Intergalactic Oxygen Surveyor), which is proposed as a dedicated soft X-ray mission to search for cosmic missing baryons. We find that WHIMs surrounding nearby clusters are detectable with a typical exposure time of one day, and thus constitute realistic and promising targets for DIOS. We also find that an X-ray emitting clump in front of Coma cluster, recently reported in the XMM-Newton observation, has a counterpart in the simulated local universe, and its observed spectrum can be well reproduced in the simulated local universe if the gas temperature is set to the observationally estimated value.
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Publications of the Astronomical Society of Japan 56(5) L29-L34 2004年 査読有りTo detect a warm-hot intergalactic medium (WHIM) associated with the large-scale structure of the universe, we observed a quasar behind the Virgo cluster with XMM-Newton. With 54 ks exposure, we marginally detected an O VIII Kα absorption line at 650.9-1.9 +0.8 in the RGS spectra, with a statistical confidence of 96.4%. The observed line center energy is consistent with the redshift of M 87, and hence the absorber is associated with the Virgo cluster. From the curve of growth, the O VIII column density was estimated to be ≳ 7 × 1016cm-2. In the EPIC spectra, excess emission was found after evaluating the hot ICM in the Virgo cluster and various background components. We inspected the RASS map of the diffuse soft X-ray background, and confirmed that the level of the north and west regions just outside of the Virgo cluster is consistent with the background model that we used, while that of the east side is significantly higher and the enhancement is comparable with the excess emission found in the EPIC data. We consider a significant portion of the excess emission to be associated with the Virgo cluster, although a possible contribution from the North Polar Spur cannot be excluded. Using the column density and the emission measure and assuming an oxygen abundance of 0.1 and an ionization fraction of 0.4, we estimate that the mean electron density and the line-of-sight distance of the warm-hot gas are ≲ 6 × 10-5cm-3 and ≳ 9Mpc. These strongly suggest detection of a WHIM in a filament associated with the Virgo cluster.
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TRANSDUCERS 2003 - 12th International Conference on Solid-State Sensors, Actuators and Microsystems, Digest of Technical Papers 2 1108-1111 2003年An X-ray microcalorimeter is a noble X-ray spectrometer that can be used for photon counting with a high energy resolution comparable to the gratings. A 2x2 X-ray microcalorimeter array was fabricated and tested. Due to the purpose of imaging applications, we have applied so-called 'mushroom-shaped' X-ray micro absorber fabricated using two-step exposure and electrodeposition process. The energy resolution of 180 eV(FWHM) at 5.9 keV was obtained with the first prototype of the X-ray microcalorimeter array using Sn micro absorber. By using Bi absorber, it is estimated that the energy resolution can be improved up to 4.5 eV.
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Digest of Papers - Microprocesses and Nanotechnology 2003 - 2003 International Microprocesses and Nanotechnology Conference, MNC 2003 182-183 2003年 査読有りIn this paper we developed through-wafer interconnections using only a simple fabrication process. The interconnection was successfully transformed into the superconducting state. A current density of 13 cm/sup 2//mA was obtained in the superconducting state. We realize high energy-resolution X-ray imaging using the superconducting through-wafer interconnections.
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Physica B: Condensed Matter 329-333(II) 1619-1620 2003年 査読有りWe present the performance of transition edge sensors (TES) using Au/Ti bilayer (operating temperature 113 mK) with fast decay time for industrial applications. The energy resolution was 9.2 eV for Mn Kα1 (designed value 3.5 eV) and the decay time 71 μs, yielding the count rate 2.3 kcps (count per sec). We found that the energy resolution was limited by excess noise. The excess noise increased in proportion to the inverse of TES resistance as decreasing the TES resistance from normal resistance. The source of excess noise might exist in the TES. © 2003 Elsevier Science B.V. All rights reserved.
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ASTRONOMISCHE NACHRICHTEN 324(1-2) 155-155 2003年 査読有り
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ASTRONOMISCHE NACHRICHTEN 324(1-2) 154-154 2003年 査読有り
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Publications of the Astronomical Society of Japan 55(3) 631-634 2003年 査読有りA possibility to detect X-rays from star-formation burst activities in proto-elliptical galaxies is considered. The X-ray flux of an emission due to inverse-Compton scattering of the cosmic microwave background (CMB) by high energy electrons accelerated in SNRs is shown to increase as z increases far beyond unity, since the local CMB flux largely increases in association with a z-increase. The flux is estimated for the case of a very high rate of type II supernovae at an initial star formation burst of a proto-elliptical galaxy and is found to be detectable with a future large X-ray telescope such as intended in the XEUS mission.
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Publications of the Astronomical Society of Japan 55(5) 879-890 2003年 査読有りMost of the cosmic baryons predicted by the big-bang nucleosynthesis have evaded direct detection. Recent numerical simulations indicate that approximately 30 to 50 percent of the total baryons in the present universe are supposed to take the form of warm/hot intergalactic medium (WHIM) whose X-ray continuum emission is very weak. To identify those missing baryons, we consider in detail the detectability of WHIM directly through the emission lines of O VII (561, 568, 574, 665 eV) and O VIII (653 eV). For this purpose, we create mock spectra of the emission lines of WHIM using a light-cone output of cosmological hydrodynamic simulations. While the predicted fluxes are generally below the current detection limit, an unambiguous detection will be feasible with a dedicated X-ray satellite mission, which we also discuss in detail. Our proposed mission is especially sensitive to a WHIM with gas temperature of T = 106-7 K and overdensity of δ = 10-100 up to a redshift of 0.3 without being significantly contaminated by the cosmic X-ray background and the Galactic emissions. Thus, such a mission provides a unique and important tool to identify a large fraction of otherwise elusive baryons in the universe.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 487(3) 488-493 2002年7月21日 査読有りThe position determination capability of the series-connected superconducting tunnel junctions (STJs) with Nb/Al/AlOx/Al/Nb junctions as a radiation detector is reported. Four groups of series-connected STJs are fabricated on a single crystal of sapphire substrate surrounding 3.5 × 3.5 mm2 detection area. The signals detected by two STJs with 1.5 mm separation give a time delay caused by the propagation of phonons, and this enables us to measure the irradiated position. Using α-particles of 5.5 MeV, we clearly distinguished the incident positions with a potential resolution of 0.16±0.07 mm (FWHM). Directional dependence in the phonon propagation in the sapphire substrate is not detected. © 2002 Elsevier Science B.V. All rights reserved.
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LOW TEMPERATURE DETECTORS 605 313-316 2002年 査読有りIn order to realize a large format (e.g. similar to 32 x 32) calorimeter array, it is essential to multiplex calorimeter signals at cryogenic temperatures without losing signal to noise ratio. For this purpose we propose a brand-new readout method, the CABBAGE ((ca) under bar lorimeter (B) under bar ridge (B) under bar iased by an (A) under barC Generator) where an AC biased calorimeters are placed in resistance bridges. In this paper we first describe the principles of CABBAGE and investigate its response and noise. We propose the large format calorimeter array readout using CABBAGEs, and discuss the new TES microcalorimeter readout method without using SQUIDs.
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Publications of the Astronomical Society of Japan 54(1) L1-L5 2002年 査読有りRecent XMM-Newton observations of clusters of galaxies have indicated the soft X-ray spectra to be inconsistent with the simple isobaric cooling flow model. There is almost no feature of the cold gas expected from the model. This shows that we have not yet understood the physics of the hot gas in clusters of galaxies well. A quantitative evaluation of the behavior of gas cooling is important not only for understanding the clusters, themselves, but also for studying cosmology and galaxy formation. To clarify the problem of this reported discrepancy, we have studied scaling relations for clusters of galaxies based on the self-similarity assumption. We also propose an observational strategy to solve this problem.
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Astrophysical Journal 578(2) 2002年 査読有り
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Publications of the Astronomical Society of Japan 54(3) 327-352 2002年 査読有りWe studied the energy spectrum and the large-scale fluctuation of the X-ray background with the ASCA GIS instrument based on the ASCA Medium Sensitivity Survey and Large Sky Survey observations. A total of 91 fields with Galactic latitude |b| > 10° were selected with a sky coverage of 50 deg22 and 4.2 Ms of exposure. For each field, non-X-ray events were carefully subtracted and sources brighter than ∼ 2 × 10-13 erg cm-2 s-1 (2-10 keV) were eliminated. Spectral fits with a single power-law model for the individual 0.7-10 keV spectra showed a significant excess below ∼ 2keV, which could be expressed by an additional thermal model with kT ≃ 0.4 keV or a steep power-law model with a photon index of Γsoft ≃ 6. The 0.5-2 keV intensities of the soft thermal component varied significantly from field to field by 1 σ = 52-5 +4% and showed a maximum toward the Galactic Center. This component is considered to be entirely Galactic. As for the hard power-law component, an average photon index of 91 fields was obtained to be Γhard = 1.412 ± 0.007 ± 0.025 and the average 2-10 keV intensity was calculated as FX hard= (6.38 ± 0.04 ± 0.64) × 10-8 erg cm-2 s-1 sr-1(1 σ statistical and systematic errors). The Galactic component is marginally detected in the hard band. The 2-10 keV intensities show a 1 σ deviation of 6.49-0.61 +0.56%, while deviation due to the reproducibility of the particle background is 3.2%. The observed deviation can be explained by the Poisson noise of the source count in the f.o.v. (∼ 0.5 deg2), even assuming a single log N-log S relation on the whole sky. Based on the observed fluctuation and the absolute intensity, an acceptable region of the log N-log S relation was derived, showing a consistent feature with the recent Chandra and XMM-Newton results. The fluctuation of the spectral index was also examined it implied a large amount of hard sources and a substantial variation in the intrinsic source spectra (Γs ≃ 1.1 ± 1.0).
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Journal of Applied Physics 90(11) 5812-5818 2001年12月 査読有りGarnets doped with rare-earth elements can be used in adiabatic demagnetization refrigerators. We have measured the specific heat and magnetization of a single crystal yttrium aluminum garnet (YAG) doped with 30% Er3+ ion at temperatures between 93 mK and 8 K under magnetic fields up to 8.0T along the 〈111〉 crystal axis. From the specific heat and magnetization, we derived consistent temperature and magnetic-field dependence of the magnetic entropy. Under zero magnetic field, the magnetic entropy begins to decrease below 2 K and becomes half of R ln 2 at ∼ 160 mK. This decrease is considered to be due to an antiferromagnetic short-range ordering among Er3+ ions. This behavior of the specific heat in the measured temperature range can be explained by a model in which both the crystalline-electric-field ground state and the first excited state are included. The operating temperature of the Er3--doped YAG as a magnetic coolant is estimated to extend down to ∼100 mK, which is lower than those with nonsubstituted garnets such as gallium-gadolinium-garnet used in the range ∼4.2-15 K. With a doping level of 30%, we estimate that ∼6 kg of Er3+-doped YAG exhibits the same cooling performance at 60 mK as the 916 g of ferric-ammonium-alum salt used for the x-ray spectrometer (microcalorimeter detectors) on the Astro-E satellite. © 2001 American Institute of Physics.
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Publications of the Astronomical Society of Japan 53(3) 421-432 2001年6月25日 査読有りWe present two-dimensional temperature maps of three bright clusters of galaxies (Abell 1060, AWM 7, and the Centaurus cluster), based on multi-pointing observations with the ASCA GIS. The temperatures were derived from hardness ratios by taking into account the XRT response. For the Centaurus cluster, we subtracted the central cool component using the previous ASCA and ROSAT results, and the metallicity gradients observed in AWM 7 and the Centaurus cluster were included in deriving the temperatures. The intracluster medium in Abell 1060 and AWM 7 is almost isothermal from the center to the outer regions with temperatures of 3.3 and 3.9 keV, respectively. The Centaurus cluster exhibits remarkable hot regions within about 30′ from the cluster center, showing a temperature increase of + 0.8 keV from the surrounding level of 3.5 keV, and the outer cool regions with lower temperatures by - 1.3 keV. These results imply that a strong merger has occurred in the Centaurus in the recent 2-3 Gyr, and that the central cool component has survived it. In contrast, the gas in Abell 1060 was well-mixed in an early period, which probably has prevented the development of a central cool component. In AWM 7, mixing of the gas should have occurred in a period earlier than the epoch of metal enrichment.
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Astrophysical Journal 549(1) 228-243 2001年3月1日 査読有りThe temperature distribution of the intracluster medium (ICM) in the Virgo Cluster of galaxies has been derived from extensive mapping observations with ASCA covering an area of 19 deg2. In the spectral analysis, the inner region within a radius of ∼60′ from M87 is characterized by an ICM temperature of kT ∼ 2.5 keV with little variation. On the other hand, the outer regions indicate significant variation of the temperature with an amplitude of about 1 keV. The temperature map was produced from the hardness ratio (HR) values with a resolution of about 5′. Besides the previously reported hot region with kT > 4 keV between M87 and M49, several hot regions with kT = 3-4 keV are detected in the cluster outskirts. The autocorrelation function for the HR variation shows that the temperature variation is correlated within a size of about 300 kpc, suggesting that gas blobs falling in the Virgo Cluster have a typical size of groups of galaxies. A correlation with the velocity dispersion of member galaxies shows that only the northwest region indicates an unusually large βspec value of 2-4. The upper limit for extended nonthermal emission in the Virgo Cluster is obtained to be LX ∼ 9 × 1041 ergs s-1 in the 2-10 keV band. We discuss that these features consistently indicate that the Virgo Cluster is in a relatively early stage of the cluster evolution.
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ASTROPHYSICAL JOURNAL 561(2) 2001年 査読有り
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Publications of the Astronomical Society of Japan 53(4) 595-604 2001年 査読有りLarge-scale distributions of hot-gas temperature and Fe abundance in the Perseus cluster have been studied with multi-pointing observations by the GIS instrument onboard ASCA. Within a radius of 20′ from the cluster center, the energy spectra requires two temperature components, in which the cool component indicates kT ∼ 2 keV and the hot-component temperature shows a significant decline from about 8 keV to 6 keV toward the center. In the outer region of the cluster, the temperature shows a fluctuation with an amplitude of about 2 keV, which suggest that a western region at ∼ 16′ from the cluster center is relatively hotter. As for the Fe abundance, a significant decline with radius is detected from 0.44 solar at the center to ∼0.1 solar at a 50′ offset region. If the observed Fe-K line intensity within 4′ from the center is suppressed by a factor of 2 due to the resonance scattering effect, the corrected Fe mass density follows the galaxy distribution. Finally, our results do not support the large-scale velocity gradients previously reported from the same GIS data.
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ASTROPHYSICAL JOURNAL 531(2) 2000年 査読有り
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Publications of the Astronomical Society of Japan 52(4) 677-684 2000年 査読有りAn ASCA observation of a region containing a Class 0 protostar IRAS 20386 + 6751 in the Lynds 1157 dark cloud, has been carried out. The protostar was not detected, and the 95% upper limit to the luminosity depends on the assumed NH: LX(0.5-10 keV) < 1.1 × 1031 erg s-1 for NH = 1 × 1023 cm-2. A Class I protostar in Lynds 1152, IRAS 20353 + 6742, in the same field was also undetected with an upper limit about three-times as much as the Lynds 1157 level. Besides these non detections, nine new X-ray sources were detected and a spectral analysis was performed for 4 sources. One object (AX J2038 + 6801) shows a hard spectrum with a temperature of kT ∼ 8 keV or a power-law photon index of ∼ 2.0 and absorbed with NH ∼ 2 × 1022 cm-2. Another fainter one (AX J2036 + 6800) has a soft spectrum with most of the emission falling below 2 keV. We examine the possible nature of these new X-ray sources based on their spectral properties.
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Publications of the Astronomical Society of Japan 52(5) 763-767 2000年 査読有りAn X-ray observation of a famous Lyman-limit quasar PKS 2145+067 at zem = 0.990 was carried out with ASCA. The source showed a 2-10 keV flux of 1.3 × 10-11 erg cm-2 s-1 (LX = 2.5 × 1046 erg s-1 for H0 = 50 km s-1 Mpc-1) described by a power-law spectrum with a photon index of the Γ = 1.63 ± 0.04. In the ASCA energy band, no excess absorption was detected, implying that absorption column density at zab = 0.791 was less than 1.6 × 1021 cm-2 if the absorbing medium had a metal abundance of 0.5 solar. A comparison with previous Einstein Observatory and ROSAT observations shows that PKS 2145+067 has increased in luminosity by a factor of 2-3 between 1991 and 1998.
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Proceedings of SPIE - The International Society for Optical Engineering 3765 664-672 1999年The filter wheel (FW) is a system to reduce the counting rates on the X-ray Spectrometer (XRS) which is the main instrument onboard the ASTRO-E satellite. The FW system consists of a rotating filter disk, controlled by a stepper motor, and a driving electronics. The disk has one open hole, 2 Be filters with thickness of 100 and 300 μm, and 3 neutral density filters with transmissions of 5, 10 and 25%. The neutral density filters are made of 200 μm thick Mo plates with 1802 pin holes. The filter positions are monitored with optical sensors. Performance verification and full environmental tests have been carried out for the flight model system. We describe the FW system and report on the results of X-ray calibration and other testings.
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 436(1-2) 1999年 査読有り
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ASTROPHYSICAL JOURNAL 519(2) 1999年 査読有り
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Publications of the Astronomical Society of Japan 51(3) 301-315 1999年 査読有りWe present ASCA results on the distributions of the metallicity and temperature in 3 bright near-by clusters: A4059, MKW 3s, and 2A 0335+096. A significant gradient in the metal abundance is detected in A4059, while other clusters suggest similar gradients with low significance. These features together with recent results on AWM 7 and Perseus clusters suggest that metals injected in the ICM are not effectively mixed in the cluster space. An analysis of the GIS data, without explicitly including the cooling flow model, shows no substantial temperature drop at large radii (at half the virial radii) for the 3 systems. This is contrary to the recent results for 30 clusters by Markevitch et al. (1998, ApJ 503, 77), who assume rather strong cooling flows. The gas mass fraction of these clusters is 10-15% within 1 Mpc, which suggests that a baryonic fraction of about 20%, including the stellar mass, is a common level in galaxy groups and clusters.
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Publications of the Astronomical Society of Japan 50(1) 19-24 1998年 査読有りThe X-ray spectrum of the distant QSO PKS 0237-233 (z = 2.223) has been studied with ASCA and ROSAT. The spectrum in the energy range 0.1 keV to 8 keV in the observer's frame is well fitted by a power-law model with a photon index of 1.54 ±0.06 absorbed by the galactic interstellar matter. The lack of excess absorption confirms that such absorption is not a universal property of the high-redshift GHz-peaked spectrum (GPS) sources. From a comparison of the Lyman α and the metal absorption lines in the optical and UV bands, small amount of X-ray absorption constrains the ionization state of the metal line system at z = 1.65 as [HI/H] > 2.5 × 10-4 and [CIV/C] > 0.11 if the metal line systems have a metal abundance of 0.1 Z(Fisheye).
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ASTROPHYSICAL JOURNAL 499(1) 1998年 査読有り
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Monthly Notices of the Royal Astronomical Society 287(2) 328-332 1997年 査読有りQ1745 + 624 is located at redshift z = 3.89, and is one of the most distant quasars observed in the X-ray band. Q1745 + 624 was clearly detected with ASCA in the 0.5-7 keV X-ray band, or in 2.4-34 keV in the quasar rest frame. If the energy spectrum is fitted by a single power law with photoelectric absorption, the photon index becomes 1.68-0.24' +0.25 and the column density NH becomes 2.1-1.4 +1.5 x 1021 cm-2, assuming the absorber to be located at z = 0. This index is steeper than that of the cosmic X-ray background. The spectrum suggests the presence of excess absorption above the Galactic column. If the absorber is at the same redshift as the quasar, then the intrinsic column density NH, is inferred to be 6.1-5.9 +10.8 x 1022cm-2, which is comparable to that seen in nearby Seyfert 2 galaxies. The spectrum shows neither flattening above ∼ 10 keV in the rest frame nor a significant Fe K line. This is in contrast to the X-ray properties of nearby Seyfert galaxies. When compared to lower redshift radio-loud quasars, Q1745 + 624 is inferred to have ∼ 10 times higher luminosity, but a very similar X-ray spectral index as well as a similar spectral energy distribution from the radio to the X-ray bands. © 1997 RAS.
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Astrophysical Journal 481(2) 821-831 1997年 査読有りHard X-ray and γ-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° and l = 40°. 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 × 1038 ergs s-1 in the 3-16 keV band. Welcome-1 observed the γ-ray ridge emission at around l ∼ 345° 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 γ-ray emissions from the Galactic ridge. © 1997. The American Astronomical Society. All rights reserved.
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ASTROPHYSICAL JOURNAL 490(1) 1997年 査読有り
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Astrophysical Journal 491(2) 638-652 1997年 査読有りX-ray spectra of the Galactic ridge emission in the Scutum arm region have been obtained with ASCA GIS and SIS in the energy range 0.7-10 keV. The observed spectra are basically of thermal emission from thin hot plasmas, and individual K emission lines from helium-like Mg, Si, S, and Fe ions are confirmed in both the GIS and SIS spectra. This means that the Galactic ridge X-ray emission cannot be explained by a single-temperature ionization-equilibrium plasma model. It cannot, however, be reproduced even if a nonequilibrium ionization model is introduced thus multiple plasma components are required. The GIS spectra are fairly well fitted by a double-temperature nonequilibrium ionization plasma model with temperatures of kT ∼ 0.8 keV and kT ∼7 keV. The softer component is found to be in an extremely low ionization state, with net ∼ 109 cm-3 s, while the harder component is in a relatively high ionization state, though not yet in a full equilibrium. The GRXE properties obtained with the GIS are carefully reexamined by the highly resolved spectral-line features with the SIS. The soft and hard components are absorbed by equivalent hydrogen columns of 0.7 × 1022 cm-2 and 4.6 × 1022 cm-2, respectively. The surface brightness of the soft and hard components at b ∼ 0° are estimated to be 1.9 × 10-6 and 5.3 × 10-7 ergs cm-2 s-1 sr-1 respectively, both in the 0.5-10 keV band. The surface brightness of the softer component extends toward significantly higher (∼2°) Galactic latitudes than the harder component, although their actual scale heights may be similar at ∼100 pc if the differences in their observable depths are taken into account. Spectral properties of the two components are seen to depend on the latitude the most noticeable effect is a rapid decrease in the Fe K line equivalent width seen in the hard component. Attempts are made to interpret the two components in terms of diffuse hot plasmas filling the interstellar space. © 1997. The American Astronomical Society. All rights reserved.
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ASTROPHYSICAL JOURNAL 488(2) L125-L128 1997年 査読有り
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Publications of the Astronomical Society of Japan 48(6) 801-811 1996年 査読有りWe have studied Cen A (NGC 5128) in the X-ray band (3-20 keV) and soft γ-ray band (40-600 keV) with the Large Area Counter (LAC) 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 (Γ ∼ 1.8) with relatively heavy absorption (NH ∼ 1.5 × 1023H cm-2) at the low-energy end and a possible break at ∼ 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 2π 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 ∼ 180 keV.
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Publications of the Astronomical Society of Japan 48(2) L15-L20 1996年 査読有りWe report on the ASCA results of hard X-ray imaging and spectroscopic observations of the galactic ridge (the Scutum arm region). The bulk of X-rays in the field of view could not be explained by an integrated emission of resolved sources, indicating that most of the galactic-ridge X-rays are due to a diffuse thin hot plasma. The X-ray luminosity of discrete sources contributing to the galactic-ridge emission was estimated to be less than -2x1033 erg s-1 in the 2-10 keV energy band. Emission lines from helium-like Si, S, and Fe ions were confirmed in the spectra, which means that the galactic ridge X-ray emission can not be explained by a single temperature ionization equilibrium plasma model. We give some constraints on the origin of the galactic-ridge emission.
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ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES 120(4) 1996年 査読有り
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ASTROPHYSICAL JOURNAL 470(2) 1996年 査読有りWe observed the BL Lac object Mrk 421 with the X-ray satellite ASCA in 1994 as part of a multifrequency observation. The 24 hr observation was conducted 1 day after the onset of a TeV flare detected by the Whipple Observatory and detected an X-ray flare, with no apparent variability in the optical, UV, and EGRET GeV flux. The ASCA 2-10 keV flux peaked at 3.7 × 10-10 ergs cm-2 s-1 and then decreased to 1.8 × 10-10 ergs cm-2 s-1 with a doubling timescale of ∼12 hr. The shape of the X-ray spectrum varied during the observation, such that the hard X-rays always led the soft X-rays, both in brightening and dimming of the source, with a lag of the 0.5-1 keV photons versus those in the 2-7.5 keV band of ∼1 hr. The rapid TeV variability indicates a compact TeV-producing region, suggesting relativistic beaming with a Doppler factor δ ≥ 5. The correlation of the flux in the X-ray and the TeV bands indicates that a high-energy tail of a single electron population is responsible for both X-rays and TeV γ-rays, with radio, IR, UV and X-rays produced via the synchrotron process and GeV and TeV γ-rays produced via Comptonization. Under the assumption that the "soft lag" observed in the X-ray band is due to the synchrotron-lifetime effects, with δ = 5, we calculate the magnetic field for the X-ray-producing region to be ∼0.2 G. The Lorentz factors γcl of the electrons responsible for the emission in the keV and TeV bands are ∼106, consistent with the values implied by the Klein-Nishina limit. © 1996. The American Astronomical Society. All rights reserved.
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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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Publications of the Astronomical Society of Japan 48(3) 395-407 1996年 査読有りWe observed two groups of galaxies, the NGC 5044 group (WP 23) and Hickson's compact group HCG 51, with ASCA. We detected an extended bright soft X-ray emission, which indicates the existence of large amounts of a hot X-ray emitting gas in both targets. The temperature of the hot gas is ∼ 1 keV for both objects, which is equivalent to their galaxy velocity dispersion. The metal abundance of the gas is 0.3-0.5 solar value for both objects, which is similar to that of rich clusters of galaxies. The Si to Fe abundance ratio is smaller than that of rich clusters of galaxies, although the iron abundances determined by the Fe-L lines are somewhat uncertain. The X-ray luminosities in the 0.5-10 keV band are 1×1043 erg s-1 and 5×1042erg s-1 for the NGC 5044 group and HCG 51, respectively, which are higher by an order of magnitude than those of X-ray bright elliptical galaxies. This makes HCG 51 one of the most X-ray luminous compact groups. Both objects have a total gravitating mass of Mtotal ∼ 2.0 × 1013 M(Fish eye sign), and a gas mass and a galaxy mass of Mgas ∼ Mgalaxy ∼ 1.5 × 1012 M(Fish eye sign). The ratios among these mass components are Mgas/Mgalaxy ∼ 1 and (Mgas + Mgalaxy)/Mtotal ∼ 0.2 within ∼350 kpc for both objects. The latter is similar to previous ROSAT results for many groups of galaxies, while the former is larger than the average value of the ROSAT-observed groups. Moreover, the metal abundances of the present two groups are significantly higher than those of the NGC 2300 group and HCG 62, and are comparable to those of clusters. These suggest that the hot-gas mass and metal abundances can scatter widely among groups, compared to the small variance found among rich clusters.
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EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy VI 2518 85-95 1995年9月1日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.
MISC
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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 2020年12月16日
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Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X 2020年12月16日
担当経験のある科目(授業)
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2003年3月 - 現在宇宙物理学特論I (隔年開講，前期） (東京大学大学院)
所属学協会
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2010年 - 現在
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 2020年11月 - 2025年3月
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日本学術振興会 科学研究費助成事業 学術変革領域研究(A) 2020年11月 - 2025年3月
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日本学術振興会 科学研究費助成事業 基盤研究(A) 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 基盤研究(B) 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 基盤研究(B) 2018年4月 - 2021年3月
教育内容やその他の工夫
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件名宇宙研での大学院教育概要宇宙の構造形成の観測的研究を主に極低温観測技術を用いて行なっている。東京大学，北里大学から大学院学生をうけいれ，大学院では，新しい検出器の開発とその応用および観測的研究の専門教育を行なう。大学院では，「誰もやったことがないこと」を自ら行なう力をつけることを目標にする。
● 指導学生等の数
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年度2018年度(FY2018)博士課程学生数1修士課程学生数1
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年度2019年度(FY2019)博士課程学生数1修士課程学生数3
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年度2020年度(FY2020)博士課程学生数1修士課程学生数3
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年度2018年度(FY2018)博士課程学生数1修士課程学生数1
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年度2019年度(FY2019)博士課程学生数1修士課程学生数3
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年度2020年度(FY2020)博士課程学生数1修士課程学生数3
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年度2022年度(FY2022)博士課程学生数3修士課程学生数2
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年度2023年度(FY2023)博士課程学生数2修士課程学生数1
● 指導学生の顕著な論文
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指導学生名高久諒太所属大学東京大学著者名, ジャーナル名, 巻号ページ（出版年）Takaku et al. , Journal of Applied Physics, 128(22), id.225302, (2020)論文タイトルBroadband, millimeter-wave anti-reflective structures on sapphire ablatedwith femto-second laserDOIhttp://doi.org/10.1063/5.0022765
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指導学生名中島裕貴所属大学Univ. of Tokyo著者名, ジャーナル名, 巻号ページ（出版年）Nakashima et al. Applied Physics Letters, 117 122601 (2020)論文タイトルLow-noise microwave SQUID multiplexed readout of 38 x-ray transition-edge sensor microcalorimetersDOIhttp://doi.org/10.1063/5.0016333
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指導学生名紺野良平所属大学Kitasato Univ.著者名, ジャーナル名, 巻号ページ（出版年）Konno et al. Journal of Low Temperature Physics 199, 654 (2019)論文タイトルDevelopment of TES micsrocalorimters with solar-axion converterDOIhttp://doi.org/10.1007/s10909-019-02257-9
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指導学生名山本亮所属大学Univ. of Tokyo著者名, ジャーナル名, 巻号ページ（出版年）Yamamoto et al. , Journal of Cosmokogy and Astrophysics, 02 (2020) 011論文タイトルA Search for a Contribution from Axion-Like Particles to the X-Ray Diffuse Background Utilizing the Earth's Magnetic FieldDOIhttp://doi.org/10.1088/1475-7516/2020/02/011
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指導学生名関谷典央所属大学University. of Tokyo著者名, ジャーナル名, 巻号ページ（出版年）Sekiya, Yamasaki, and Mitsuda, Publications of Astronomical Society in Japan, 68(SP1), S31 (2016)論文タイトルSearch for a keV Signature of Radiatively Decaying Dark Matter with Suzaku XIS Observations of the X-ray Diffuse BackgroundDOIhttp://doi.org/10.1093/pasj/psv081
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指導学生名三石郁之所属大学Univ. of Tokyo著者名, ジャーナル名, 巻号ページ（出版年）Mitsuishi, Yamasaki, and Takei, Publications of Astronomical Society in Japan, 65, 44 (2013)論文タイトルAn X-Ray Study of the Galactic-Scale Starburst-Driven Outflow in NGC 253DOIhttp://doi.org/10.1093/pasj/65.2.44
● 専任大学名
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専任大学名東京大学（University of Tokyo)
● 所属する所内委員会
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所内委員会名ナノエレクトロニクスクリーンルーム運営委員会
