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
240-
ASTROPHYSICAL JOURNAL 680(2) 2008年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 2008年 査読有り
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PASJ : publications of the Astronomical Society of Japan 60(1) S333-S342 2008年 査読有り
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Publications of the Astronomical Society of Japan 60(4) 695-705 2008年 査読有りThe results from Suzaku X-ray Imaging Spectrometer (XIS) observations of relaxed cluster of galaxies, Abell 2052, are presented. Offset pointing data were used to estimate the Galactic foreground emission in the direction of the cluster. Significant soft X-ray excess emission above this foreground, the intracluster medium emission, and other background components was confirmed and resolved both radially and spectroscopically. This excess can be described either by (a) local variations of known Galactic emission components or by (b) an additional thermal component with a temperature of about 0.2 keV, possibly associated with the cluster. The radial temperature and metallicity profiles of the intracluster medium were measured within ∼ 20′ in radius (about 60% of the virial radius) from the cluster center. The temperature drops radially to 0.5-0.6 of the peak value at a radius of ∼ 15′. The gas-mass-weighted metal abundance averaged over the observed region was found to be 0.21 ± 0.05 times solar. © 2008. Astronomical Society of Japan.
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Astrophysical Journal 667(1) L41-L44 2007年9月20日 査読有りWe studied the properties of the intracluster medium (ICM) in two clusters of galaxies (AWM 7 and Abell 1060) and two groups (HCG 62 and NGC 507) with the X-ray observatory Suzaku. Based on spatially resolved energy spectra, we measured for the first time precise cumulative ICM metal masses within 0.1 and ∼0.3r180. Comparing our results with supernova nucleosynthesis models, the number ratio of Type II (SNe II) to Type Ia (SNe Ia) is estimated to be ∼3.5, assuming the metal mass in the ICM is represented by the sum of products synthesized in SNe Ia and SNe II. Normalized by the K-band luminosities of present galaxies, and including the metals in stars, the integrated number of past SN II explosions is estimated to be close to or somewhat higher than the star formation rate determined from Hubble Deep Field observations. © 2007. The American Astronomical Society. All rights reserved.
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IEEE Nuclear Science Symposium Conference Record 4 2526-2531 2007年 査読有りWe report in-flight status of the X-ray detectors on board the Suzaku observatory, the 5th X-ray astronomy satellite of Japan launched on July 10, 2005. Suzaku is equipped with two types of Instruments: one is the X-ray Imaging Spectrometers (XISs) and the other is Hard X-ray Detector (HXD). XIS utilizes the X-ray CCD camera in combination with the grazing-incidence X-ray telescope. HXD is a non-imaging, hybrid detector utilizing Si PIN diodes and GSO/BGO phoswich counters. Suzaku takes a low-earth, circular orbit with an altitude of 560 km and an inclination of 31 deg. This means that Suzaku goes through the south atlantic anomaly about 1/3 of its revolutions. This has a large impact on the in-flight performance of XIS and HXD, which is reported in detail in the present paper. © 2007 IEEE.
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Progress of Theoretical Physics Supplement (169) 79-83 2007年 査読有りJoint analysis of Suzaku/Chandra emission/absorption lines were conducted to constrain the density and geometry of hot gas along two lines of sights of LMC X-3 and 4U 1820-303. Because significant foreground line emissions may exist, the Suzaku emission data must be analyzed with spacial cares. The present results imply the hot gas to extend to the galacticdisk scale or more for the LMC X-3 direction. However, the present simple model fails to explain the results for the 4U1820-303 directions.
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Publications of the Astronomical Society of Japan 59 2007年 査読有り
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 2007年 査読有り
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PASJ : publications of the Astronomical Society of Japan 59(1) S77-S112 2007年 査読有り
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PASJ : publications of the Astronomical Society of Japan 59(1) S339-S349 2007年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S1-S7 2007年 査読有りHigh-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described. © 2007. Astronomical Society of Japan.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S327-S338 2007年 査読有りThe metallicity distribution in the Fornax cluster was studied with the XIS instrument on board the Suzaku satellite. The K-shell lines of O and Mg were resolved clearly, and the abundances of O, Mg, Si, S, and Fe were measured with great accuracy. The region within a 4' radius of NGC 1399 shows approximately solar abundances of Fe, Si, and S, while the O/Fe and Mg/Fe abundance ratios are about 0.4-0.5 and 0.7 in solar units, respectively. In the outer region of the radius range 6' < r < 23', the Fe and Si abundances drop to 0.4-0.5 solar and show no significant gradient within this region. The abundance ratios, O/Fe and Mg/Fe, are consistent with those in the central region. We also measured the Fe abundance around NGC 1404 to be approximately solar, and the 0, Ne, and Mg abundances to be 0.5-0.7 times the Fe level. A significant relative enhancement of Fe within 130kpc of NGC 1399 and in NGC 1404 indicates an origin in SN Ia, in contrast to the species 0, Ne, and Mg, which reflect the stellar metallicity. The mass-to-light ratios for O and Fe within 130kpc of NGC 1399 are over an order of magnitude lower than those in rich clusters, reflecting the metal enrichment history of this poor cluster.
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PASJ : publications of the Astronomical Society of Japan 59(SP1) 113-132 2007年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(SP1) 245-255 2007年 査読有りWe have observed the diffuse X-ray emission from the Galactic Center (GC) using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy resolution and the low-background orbit provided excellent spectra of the GC diffuse X-rays (GCDX). The XIS found many emission lines in the GCDX near the energy of K-shell transitions of iron and nickel. The most pronounced features are Fe I Kα at 6.4 keV and K-shell absorption edge at 7.1 keV, which are from neutral and/or low ionization states of iron, and the K-shell lines at 6.7 keV and 6.9 keV from He-like (Fe XXV Kα) and hydrogenic (Fe XXVI Lyα) ions of iron. In addition, Ka lines from neutral or low ionization nickel (Ni I Kα) and He-like nickel (NiXXVII Kα), Fe I Kβ, Fe XXV Kβ, Fe XXVI Lyβ, Fe XXV Kγ, and Fe XXVI Lyγ were detected for the first time. The line center energies and widths of Fe XXV Kα and Fe XXVI Lyα favor a collisional excitation plasma for the origin of the GCDX. The electron temperature determined from the line flux ratio of Fe XXV Kα/Fe XXV Kβ is similar to the ionization temperature determined from that of Fe XXV Kα/Fe XXVI Lyα. Thus it would appear that the GCDX plasma is close to ionization equilibrium. The 6.7 keV flux and temperature distribution to the galactic longitude is smooth and monotonic, in contrast to the integrated point source flux distribution. These facts support the hypothesis that the GCDX is truly diffuse emission rather than the integration of the outputs of a large number of unresolved point sources. In addition, our results demonstrate that the chemical composition of Fe in the interstellar gas near the GC is constrained to be about 3.5 times solar abundance. © 2007. Astronomical Society of Japan.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S141-S150 2007年 査読有り
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Publications of the Astronomical Society of Japan 59(2) 299-317 2007年 査読有りWe carried out observations of the central and 20′ east offset regions of the cluster of galaxies Abell 1060 with Suzaku. Spatially resolved X-ray spectral analysis has revealed temperature and abundance profiles of Abell 1060 out to 27′ ≃ 380 h70 -1 kpc, which corresponds to ∼ 0.25 r180. Temperature decrease of the intra-cluster medium from 3.4 keV at the center to 2.2 keV in the outskirt region was clearly observed. The abundances of Si, S, and Fe also decrease by more than 50% from the center to the outer region, while Mg shows a fairly constant abundance distribution at ∼ 0.7 solar within r ≲ 17′. O shows a lower abundance of ∼ 0.3 solar in the central region (r ≲ 6′), and indicates a similar feature with Mg however, it is sensitive to the estimated contribution of the Galactic components of k T1 ≃ 0.15 keV and k T2 ≃ 0.7 keV in the outer annuli (r ≳ 13′). Systematic effects due to the point-spread function tails, contamination on the XIS filters, instrumental background, cosmic and/or Galactic X-ray background, and the assumed solar abundance tables were carefully examined. The results on the temperature and abundances of Si, S, and Fe are consistent with those derived by XMM-Newton at r ≲ 13′. The formation and metal-enrichment process of the cluster are discussed based on the present results. © 2007. Astronomical Society of Japan.
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Progress of Theoretical Physics Supplement (169) 109-112 2007年 査読有りThe Galactic center (GC) region has been known to exhibit strong enhancements of hot diffuse plasma, which is characterized by the highly ionized Fe-K fluorescence line. Based on past X-ray observations with Ginga, ASCA, and RXTE, in the Galactic plane or bulge region, a non-thermal emission, so-called the "hard-tail", has been confirmed to dominate the hard X-ray flux above 10 keV, and an association was found between surface brightnesses of the thermal and non-thermal components despite the completely different emission mechanism. Therefore, it is obviously important to investigate an existence of the hard-tail at GC with the unprecedented sensitivity of the HXD onboard Suzaku. By combining its narrow field-of-view of 30' and X-ray images simultaneously obtained by the XIS below 10 keV, an extensive investigation of spectral and spatial properties of the GC hard X-ray emission can be for the first time realized. We will report on results from seven pointings around GC, with a total exposure of 300 ks, performed in the performance verification phase of Suzaku. Strong hard X-ray signals were clearly detected in every observation by HXD-PIN in 10-70 keV range with a few tenth mCrab level intensities.
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PASJ : publications of the Astronomical Society of Japan 59(1) 269-282 2007年 査読有り
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 559(2) 432-435 2006年4月14日 査読有りBi films that we fabricated with vacuum-evaporation deposition show a crystal structure very similar to that of bulk Bi. However they have granular structure on sub-micron scales, and the electrical resistance increases at low temperatures, which is opposite to bulk Bi. A TES microcalorimeter with a Bi absorber shows an energy resolution significantly degraded compared to the baseline resolution. A thermal model of the calorimeter based on the present experimental results indicates that a position dependence of the pulse height and rise time degrades the energy resolution. The position dependence is further considered to be due to mismatch between the rise time of pulse which is mostly determined by the thermal conductance between Bi and TES and the thermal diffusion time in the Bi absorber. © 2006 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 559(2) 811-813 2006年4月14日 査読有りIn a magnetic summation method, TES and SQUID driving circuits are isolated and thus small crosstalk and stray impedance are expected. Since a FLL circuit with a large bandwidth and a small noise level is required for a SQUID, we designed and produced an electronics to meet our design of multiplexing with an 8-input SQUID. The FLL circuit achieved an open loop-gain bandwidth product of 8 MHz with 1 m wire length, which is enough for a TES to be operated with a bias current of 70 μ A, and a noise level of 30 pA / sqrt(Hz). © 2006 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 559(2) 539-541 2006年4月14日 査読有りWe succeeded in fabricating 256-pixel arrays of Ti/Au transition edge sensor (TES) microcalorimeters with electrodeposited microabsorbers made of Bi, and report on their test results. We confirmed all pixels tested so far were alive, however most of the microabsorbers were stripped off during cooling cycles. We investigated some pixels by irradiating with 5.9 keV X-rays, and confirmed that they actually worked as microcalorimeters. The X-ray pulses are represented by a sum of two components with different decay times. The ratio of the two components fluctuates from pulse to pulse, which limits the energy resolution to ∼ 200 eV. We discuss the pulse shape of two decay-time components considering thermal conductivities, i.e., inside microabsorbers, between microabsorbers and TES. © 2005 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 559(2) 832-834 2006年4月14日 査読有りWe will report on the performance of a first order SQUID gradiometer developed for the readout of the magnetic microcalorimeters. The SQUID is designed to operate at temperatures below 0.1 K with flux noise level lower than 1 μ Φ0 / sqrt(Hz) in a magnetic field of 3.5 mT at its washers. It has a baseline of 500 μ m and washer size of 50 μ m in diameter. To produce an ambient magnetic field in a persistent current mode, field coils with a superconducting short equipped with a heater as a switch are integrated on the same chip. Care was taken to decrease the heat input generated by shunt resistors and cooling fins were attached to them to minimize the over-heating of the electrons in the shunts. In order not to degrade the performance by the readout circuit, the SQUID gradiometer is connected to and read out through a low noise series SQUID amplifier. © 2005 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 559(2) 790-792 2006年4月14日 査読有りIn frequency-domain Superconducting Quantum Interference Device (SQUID) multiplexing for Transition Edge Sensor (TES) readout, a magnetic field summation method utilizing multi-input SQUIDs has a fundamental merit of small degradation of signal-to-noise ratio. Independent wiring without common impedance avoids the cross talk current, and the current induced by magnetic coupling between the input coils is suppressed by the direct feedback at the summing point. A multi-input SQUID which has 8 input coils has been fabricated and requirements for Flux Locked Loop (FLL) circuits are summarized. © 2006 Elsevier B.V. All rights reserved.
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IEICE Transactions on Electronics E89-C(2) 98-104 2006年 査読有りIn frequency-domain multiplexing (FDM) for TES signals, a magnetic field summation method utilizing a multi-input SQUID has the fundamental merit of small degradation of the signal-to-noise ratio. We formulated shifts of the operation point due to a common impedance and cross talk currents. These effects are evaluated for several FDM methods, and the requirements for the bandwidth and filters are summarized. The design parameters of multi-input SQUIDs and a flux locked loop driving circuits are also presented. Copyright © 2006 The Institute of Electronics, Information and Communication Engineers.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 58(4) 657-671 2006年 査読有りWe discuss the delectability of a Warm/Hot Intergalactic Medium (WHIM) via absorption lines toward bright point sources with a future X-ray satellite mission, XEUS. While we consider bright QSOs as specific examples, the methodology can be applied to bright gamma-ray burst afterglows. We created mock absorption spectra for bright QSOs (more than 20 QSOs over all sky) using the light-cone output of a cosmological hydrodynamic simulation. We assumed that the WHIM is under collisional and photo-ionization equilibrium. If WHIM has a constant metallicity of Z = 0.1 Z(circle dot), approximately 2 O VII absorption line systems with > 3 sigma will be detected on average along a random line-of-sight toward bright QSOs up to z = 0.3 for a 30 ks exposure.
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Publications of the Astronomical Society of Japan 58(4) 695-702 2006年 査読有りWe present results from an XMM-Newton observation of the non-cooling flow cluster Abell 1060. The large effective area of XMM-Newton enabled us to investigate the nature of this cluster in unprecedented detail. From the observed surface brightness distribution, we found that the gravitational mass distribution is well described by the Navarro-Frenk-White (1997, ApJ, 490, 493) profile, but with a central density slope of ∼1.5. We undoubtedly detected a radial temperature decrease of as large as ∼30% from the center to the outer region (r ∼ 13′), which seems to be much larger than that expected from the temperature profile averaged over nearby clusters. We established that the temperature of a region ∼ 7′ southeast of the center is higher than the azimuthally averaged temperature of the same radius by ∼ 20%. Since the pressure of this region already reaches equilibrium with the environment, the temperature structure can be interpreted as having been produced between 4 × 107 yr (the sound-crossing time) and 3 × 108yr (the thermal conduction time) ago. We found that a high-metallicity blob located at ∼1′.5 northeast of NGC 3311 is more extended, and its iron mass of 1.9 × 107 M⊙ is larger by an order of magnitude than that estimated from our Chandra observation. The amount of iron can still be considered as being injected solely from the elliptical galaxy NGC 3311. © 2006. Astronomical Society of Japan.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 58(4) 719-742 2006年 査読有りWe present results from Chandra and XMM-Newton observations of a bright group of galaxies, HCG 62. There are two cavities at about 30 northeast and 20" southwest of the central galaxy in the Chandra image. The energy spectrum shows no significant change in the cavity compared with that in the surrounding region. The radial X-ray profile is described by the sum of the 3-beta components with core radii of about 2, 10, and 160 kpc. We studied the radial distributions of the temperature and the metal abundance with a joint spectral fit for both data; two temperatures were required in the inner r < 2' (36 kpc) region. A sharp drop of the temperature at r similar to 5' implies a gravitational mass density even lower than the gas density, suggesting that the gas may not be in hydrostatic equilibrium. The Fe and Si abundances are 1-2 solar at the center, and drop to about 0.1 solar at r similar to 10'. The O abundance is less than 0.5 solar, and shows a flatter profile. The observed metal distribution supports the view that iron and silicon are produced by type la supernova (SN Ia) in the central galaxy, while galactic winds by SN II have caused a wide distribution of oxygen. The supp
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Publications of the Astronomical Society of Japan 57(5) 743-749 2005年 査読有りWe present results from an XMM-Newton observation of the head-tail radio galaxy IC 310 located in the southwest region of the Perseus cluster. The spectrum is well fitted by an absorbed power-law model with a photon index of 2.50 ± 0.02 without significant absorption excess. The X-ray image shows a point-like emission at IC 310 without any sign of a structure correlated with the radio halo tail. The temperature of the intracluster medium surrounding IC 310 declines as a function of distance from the cluster center, from kT ∼ 6keV in the northeast corner of the field of view to about 3 keV in the southwest region. Although we do not find any sharp edges in the surface brightness profile, a brightness excess of about 20% over a smooth β model is seen. The temperature also rises by about 10% in the same region. This indicates that the IC 310 region is a subcluster probably infalling into the Perseus cluster, and the gas in front of IC 310 towards the Perseus cluster is likely to be compressed by the large-scale motion, which supports the view that the IC 310 system is undergoing a merger. © 2005. Astronomical Society of Japan.
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Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 43(9 A) 6477-6478 2004年9月 査読有りWe report on the detection of signals from 5.5 MeV α-particles with a Au:Er magnetic calorimeter. Since this device shows strong temperature dependence on magnetization, the incident particle energy is measured by a change in the degree of magnetization using a superconducting quantum interference device (SQUID). We fabricated a sensor made of Au doped with ∼0.3% Er in our laboratory, and irradiated it with 241 Am in a dilution refrigerator. The detected signals showed an average pulse height of 7 mV, corresponding to a 2 pA m2 change in the magnetic moment of the sensor, at a bath temperature of 80 mK under an external magnetic field of 0.1 mT.
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Astrophysical Journal 605(2 I) 793-799 2004年4月20日 査読有りWe searched for absorption lines of highly ionized O and Ne in the energy spectra of two low-mass X-ray binaries, 4U 1820-303 in the globular cluster NGC 6624 and Cyg X-2, observed with the Chandra LETG, and detected O VII, O VIII, and Ne IX absorption lines for 4U 1820-303. The equivalent width of the O VII Kα line was 1.19-0.30+0.47 eV (90% errors), and the significance was 6.5 σ. Absorption lines were not detected for Cyg X-2 with a 90% upper limit on the equivalent width of 1.06 eV for O VII Kα. The intrinsic line width was not resolved, and an upper limit corresponding to a velocity dispersion of b = 420 km s-1 was obtained for the O VII Kα line of 4U 1820-303. The ion column densities were estimated from the curve-of-growth analysis, assuming several different values of b. The absorption lines observed in 4U 1820-303 are likely due to hot interstellar medium, because O will be fully photoionized if the absorbing column is located close to the binary system. The velocity dispersion is restricted to b = 200-420 km s-1 from consistency between O VII Kα and Kβ lines, the Ne/O abundance ratio, and H column density. The average temperature and the O VII density are estimated to be log T(K) = 6.2-6.3 and nO VII = (0.7-2.3) x 10-6 cm-3, respectively. The difference of O VII column densities for the two sources may be connected to the enhancement of the soft X-ray background (SXB) toward the Galactic bulge region. Using the polytrope model of hot gas to account for the SXB, we corrected for the density gradient and estimated the midplane O VII density at the solar neighborhood. The scale height of hot gas is then estimated using the active galactic nuclei (AGN) absorption lines. It is suggested that a significant portion of both the AGN absorption lines and the high-latitude SXB emission lines can be explained by the hot gas in our Galaxy.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 520(1-3) 431-434 2004年3月11日 査読有りWe are developing a Ti/Au TES microcalorimeter array for future Japanese X-ray astronomy missions. The goal is an energy resolution of 2-5 eV at 6 keV, and an array of 100-1000 pixels to achieve a geometrical area of 1 cm 2 and a moderate spatial resolution simultaneously. The energy resolution was improved to ∼6 eV at 6 keV with a very fast time constant (< 100 μs). To achieve a high coverage fraction, it is necessary to fabricate mushroom-shaped X-ray microabsorbers. We are developing an electrodeposition fabrication technique that is suitable for our process. Sn was used as absorber material, but the energy resolution was not good due to the existence of long-lived quasiparticles. Bi is also used, and the process is under optimization now. The readout strategy is to multiplex signals in the frequency domain, using a bridge circuit. So far, we succeeded in multiplexing two pixels modulated with 50 and 20 kHz at 440 mK. The energy resolution obtained at 110 mK was 33 eV(25 kHz). © 2003 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 520(1-3) 452-455 2004年3月11日 査読有りPerformance of microcalorimeters with a Ti/Au transition-edge sensor (TES) and an electrodeposited absorber has been investigated. The absorbers are in a mushroom-shape made of Sn or Bi. With an Sn absorber we observed a long time scale component of 1.8 ms for X-ray pulses, which is due presumably to recombination of quasiparticles into phonons. As a result, the energy resolution is not good with the Sn absorber. Better energy resolution of 28±1 eV was obtained with an incomplete-shaped Bi absorber, although the long component was also seen with smaller level. A calorimeter with only a neck of the Au seed layer for the electrodeposition had the best energy resolution of 6.3±0.4 eV in spite of saturated pulses and relatively high transition temperature of 210 mK. © 2003 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 520(1-3) 566-569 2004年3月11日 査読有りProperties of Transition-Edge Sensor (TES) microcalorimeters operated with AC bias are studied utilizing the calorimeter Wheatstone bridge circuit called Calorimeter Bridge Biased by an AC Generator (CABBAGE). The CABBAGE eliminates the AC carrier significantly, thus enables us to study the AC responses of the TES with high sensitivity. We tested two kinds of TES devices operating at 110 and 440 mK, respectively. With the 110 mK device biased with 25 kHz, an energy resolution of 28 eV is obtained for Mn Kα line. On the other hand, we multiplexed the signals from two 440 mK device biased with 50 and 20 kHz, respectively, and obtained 167 and 271 eV energy resolutions. Even at the balance point of the bridge, AC signal did not disappear and odd-order harmonics were observed. They are considered to arise from the current dependence of the TES resistance, which is characterized by β = dlogR/dlogI. Numerical solution for the CABBAGE response can reproduce the experimental results well if β = 0.24±0.02. Since the harmonics may cause severe problem in the SQUID operation even after attenuated by a band-pass filter, especially at high bias frequency operation such as several hundred kHz, it is important to make β small. © 2003 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 520(1-3) 456-459 2004年3月11日 査読有りWe have developed multi-pixel TES microcalorimeters in order to realize high-energy resolution and X-ray imaging. A Sn absorber and a Bi absorber were formed on Si3N4 and SiO2 membrane using two-step exposure photolithography and electrodeposition. A FEM analysis was carried out to investigate the performance of the X-ray microabsorbers. In addition, a superconducting through-wafer interconnection was demonstrated considering the future X-ray imager using microcalorimeters. Detail of the fabrication techniques, characteristics and simulation results of two types of the microabsorbers, as well as those of the calorimeters are described. © 2003 Elsevier B.V. All rights reserved.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 520(1-3) 340-343 2004年3月11日 査読有りWe are developing transition edge sensor (TES) microcalorimeter arrays for future Japanese astronomy missions. Although 6.6 eV energy resolution for 5.9 keV and 74 μs decay time are achieved, our energy resolution was limited by the excess noise of unknown origin. The dominant noise showed 1/R dependence and it only appeared when the current through the TES, I, is larger than 10 μA. This is explained if we assume a constant voltage noise source with a level of ∼2(4kTCRn)1/2. We also investigated the influence of I on the TES performance and found the TES sensitivity α is reduced when the ratio of current to the critical current I/IC is large. It can explain the reduction of α observed when operated without a magnetic shield. We also found a strong correlation between IC and α or the baseline width. Thus, we conclude that IC is an essential parameter for the TES performance. © 2003 Elsevier B.V. All rights reserved.
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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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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.
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 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
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日本学術振興会 科学研究費助成事業 基盤研究(S) 2014年5月 - 2019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
