Curriculum Vitaes
Profile Information
- Affiliation
- Professor, Institute of Space and Astronautical Science, Department of Astrophysics, Japan Aerospace Exploration Agency
- J-GLOBAL ID
- 201801002962836691
- researchmap Member ID
- B000323419
- External link
Research Interests
2Research Areas
1Research History
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Aug, 2005 - Present
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Apr, 1992 - Jul, 2005
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Aug, 2001 - Dec, 2004
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Apr, 1991 - Mar, 1992
Education
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Apr, 1986 - Mar, 1991
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Apr, 1980 - Mar, 1986
Committee Memberships
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Nov, 2020 - Present
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Apr, 2020 - Present
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Apr, 2020 - Present
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Apr, 2020 - Present
Papers
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Publications of the Astronomical Society of Japan, Oct 7, 2025
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The Astrophysical Journal Letters, 982(1) L5-L5, Mar 12, 2025Abstract We present XRISM Resolve observations of the core of the hot, relaxed galaxy cluster Abell 2029 (A2029). We find that the line-of-sight bulk velocity of the intracluster medium (ICM) within the central 180 kpc is at rest with respect to the brightest cluster galaxy, with a 3σ upper limit of ∣v bulk∣ < 100 km s−1. We robustly measure the field-integrated ICM velocity dispersion to be σ v = 169 ± 10 km s−1, obtaining similar results for both single-temperature and two-temperature plasma models to account for the cluster cool core. This result, if ascribed to isotropic turbulence, implies a subsonic ICM with Mach number and a nonthermal pressure fraction of 2.6 ± 0.3%. The turbulent velocity is similar to what was measured in the core of the Perseus cluster by Hitomi, but here in a more massive cluster with an ICM temperature of 7 keV, the limit on the nonthermal pressure fraction is even more stringent. Our result is consistent with expectations from simulations of relaxed clusters, but it is on the low end of the predicted distribution, indicating that A2029 is an exceptionally relaxed cluster with no significant impacts from either a recent minor merger or active galactic nucleus activity.
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Nature, 638(8050) 365-369, Feb 12, 2025
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International Journal of Modern Physics A, Jan 29, 2025Recent direct measurements of the energy spectra of the charged cosmic ray have revealed unexpected spectral features, most notably the onset of a progressive hardening at few hundreds of GeV/n not only of proton and He spectra but also observable for heavier nuclei. Thus, the study of the spectra behavior of heavy elements may shed light on understanding propagation and acceleration phenomena in our Galaxy. In particular, Fe and Ni provide favorable conditions for observations thanks to the low background contamination from spallation of higher mass elements they are affected by. The CALorimetric Electron Telescope, CALET, has been measuring high-energy cosmic rays on the International Space Station since October 2015. The instrument consists of two layers of segmented plastic scintillators, a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter and a 27 radiation length thick PWO calorimeter. It identifies the charge of individual elements up to Ni and beyond and it measures the energy of cosmic-ray nuclei providing a direct measurement of their spectra. In this contribution, the iron and nickel spectra, resulted after 5 years of data acquisition, are presented in the energy range between 10 and 2000 GeV/n and between 8.8 and 240 GeV/n, respectively. The analysis procedure and the assessment of systematic errors are detailed, in addition to the ratio between the two fluxes. Both spectra show similar shape and energy dependence.
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Publications of the Astronomical Society of Japan, Dec 26, 2024Abstract Sagittarius A East is a supernova remnant with a unique surrounding environment, as it is located in the immediate vicinity of the supermassive black hole at the Galactic center, Sagittarius A$^{*}$. The X-ray emission of the remnant is suspected to show features of overionized plasma, which would require peculiar evolutionary paths. We report on the first observation of Sagittarius A East with the X-Ray Imaging and Spectroscopy Mission (XRISM). Equipped with a combination of a high-resolution microcalorimeter spectrometer and a large field-of-view CCD imager, we for the first time resolved the Fe xxv K-shell lines into fine structure lines and measured the forbidden-to-resonance intensity ratio to be $1.39 \pm 0.12$, which strongly suggests the presence of overionized plasma. We obtained a reliable constraint on the ionization temperature just before the transition into the overionization state, of $\gt\! 4\:$keV. The recombination timescale was constrained to be $\lt\! 8 \times 10^{11} \:$cm$^{-3}\:$s. The small velocity dispersion of $109 \pm 6\:$km$\:$s$^{-1}$ indicates a low Fe ion temperature $\lt\! 8\:$keV and a small expansion velocity $\lt\! 200\:$km$\:$s$^{-1}$. The high initial ionization temperature and small recombination timescale suggest that either rapid cooling of the plasma via adiabatic expansion from dense circumstellar material or intense photoionization by Sagittarius A$^{*}$ in the past may have triggered the overionization.
Misc.
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVI, 521 205-208, 2019
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVIII, 523 515-518, 2019
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ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVI, 521 46-49, 2019
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Publications of the Astronomical Society of Japan, 70(3), Feb 14, 2018We present results from the Hitomi X-ray observation of a young<br /> composite-type supernova remnant (SNR) G21.5$-$0.9, whose emission is dominated<br /> by the pulsar wind nebula (PWN) contribution. The X-ray spectra in the 0.8-80<br /> keV range obtained with the Soft X-ray Spectrometer (SXS), Soft X-ray Imager<br /> (SXI) and Hard X-ray Imager (HXI) show a significant break in the continuum as<br /> previously found with the NuSTAR observation. After taking into account all<br /> known emissions from the SNR other than the PWN itself, we find that the Hitomi<br /> spectra can be fitted with a broken power law with photon indices of<br /> $\Gamma_1=1.74\pm0.02$ and $\Gamma_2=2.14\pm0.01$ below and above the break at<br /> $7.1\pm0.3$ keV, which is significantly lower than the NuSTAR result ($\sim9.0$<br /> keV). The spectral break cannot be reproduced by time-dependent particle<br /> injection one-zone spectral energy distribution models, which strongly<br /> indicates that a more complex emission model is needed, as suggested by recent<br /> theoretical models. We also search for narrow emission or absorption lines with<br /> the SXS, and perform a timing analysis of PSR J1833$-$1034 with the HXI and<br /> SGD. No significant pulsation is found from the pulsar. However, unexpectedly,<br /> narrow absorption line features are detected in the SXS data at 4.2345 keV and<br /> 9.296 keV with a significance of 3.65 $\sigma$. While the origin of these<br /> features is not understood, their mere detection opens up a new field of<br /> research and was only possible with the high resolution, sensitivity and<br /> ability to measure extended sources provided by an X-ray microcalorimeter.
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SPACE TELESCOPES AND INSTRUMENTATION 2018: ULTRAVIOLET TO GAMMA RAY, 10699, 2018
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Aug 31, 2017This document presents HiPS, a hierarchical scheme for the description,<br /> storage and access of sky survey data. The system is based on hierarchical<br /> tiling of sky regions at finer and finer spatial resolution which facilitates a<br /> progressive view of a survey, and supports multi-resolution zooming and<br /> panning. HiPS uses the HEALPix tessellation of the sky as the basis for the<br /> scheme and is implemented as a simple file structure with a direct indexing<br /> scheme that leads to practical implementations.
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ASTROPHYSICAL JOURNAL LETTERS, 837(1), Mar, 2017
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years of MAXI: monitoring X-ray Transients, 2017
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Meeting Abstracts of the Physical Society of Japan, 71 503-503, 2016
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Dec 1, 2015The Galactic Ridge X-ray Emission (GRXE) spectrum has strong iron emission<br /> lines at 6.4, 6.7, and 7.0~keV, each corresponding to the neutral (or<br /> low-ionized), He-like, and H-like iron ions. The 6.4~keV fluorescence line is<br /> due to irradiation of neutral (or low ionized) material (iron) by hard X-ray<br /> sources, indicating uniform presence of the cold matter in the Galactic plane.<br /> In order to resolve origin of the cold fluorescent matter, we examined the<br /> contribution of the 6.4~keV line emission from white dwarf surfaces in the hard<br /> X-ray emitting symbiotic stars (hSSs) and magnetic cataclysmic variables (mCVs)<br /> to the GRXE. In our spectral analysis of 4~hSSs and 19~mCVs observed with<br /> Suzaku, we were able to resolve the three iron emission lines. We found that<br /> the equivalent-widths (EWs) of the 6.4~keV lines of hSSs are systematically<br /> higher than those of mCVs, such that the average EWs of hSSs and mCVs are<br /> $179_{-11}^{+46}$~eV and $93_{-3}^{+20}$~eV, respectively. The EW of hSSs<br /> compares favorably with the typical EWs of the 6.4~keV line in the GRXE of<br /> 90--300~eV depending on Galactic positions. Average 6.4~keV line luminosities<br /> of the hSSs and mCVs are $9.2\times 10^{39}$ and $1.6\times<br /> 10^{39}$~photons~s$^{-1}$, respectively, indicating that hSSs are intrinsically<br /> more efficient 6.4~keV line emitters than mCVs. We compare expected<br /> contribution of the 6.4 keV lines from mCVs with the observed GRXE 6.4 keV line<br /> flux in the direction of $(l,b) \approx (28.5\arcdeg, 0\arcdeg$). We conclude<br /> that almost all the 6.4 keV line flux in GRXE may be explained by mCVs within<br /> current undertainties of the stellar number densities, while contribution from<br /> hSSs may not be negligible.
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日本理科教育学会全国大会要項, (65) 198-198, 2015
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大会講演予講集, 107 295-295, 2015
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Dec 3, 2014In this white paper we describe the prospects for ASTRO-H for the study of<br /> outflows from active galactic nuclei. The most important breakthroughs in this<br /> field are expected to arise from the high spectral resolution and sensitivity<br /> in the Fe-K band, combined with broad-band sensitivity over the full X-ray band<br /> and spectral capabilities also at lower energies. The sensitivity in the Fe-K<br /> region allows to extend the absorption measure distribution of the outflow out<br /> to the highest ionisation states accessible, where observations with current<br /> X-ray missions indicate that most of the outflowing gas is to be found. Due to<br /> the high-resolution and sensitivity it will also be able to give the definitive<br /> proof for the existence of ultra-fast outflows, and if so, characterise their<br /> physical properties in great detail. These ultra-fast outflows carry very large<br /> amounts of energy and momentum, and are of fundamental importance for feedback<br /> studies. We show how the ASTRO-H observations in general can help to constrain<br /> numerical models for outflows. The link to reflection and emission processes is<br /> also discussed, as well as the possible relation between outflows and<br /> relativistic emission lines. Finally, we discuss the prospects for other<br /> related categories of objects like BAL quasars, partially covered sources and<br /> Compton thick outflows.
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SPACE TELESCOPES AND INSTRUMENTATION 2014: ULTRAVIOLET TO GAMMA RAY, 9144, 2014
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40th COSPAR Scientific Assembly. Held 2-10 August 2014, in Moscow, Russia, Abstract id. E1.5-54-14., 2014
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Astrophysical Journal, 779(1), Dec 10, 2013
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JAXA research and development report, 12 29-37, Mar, 2013MAXI, the only all-sky X-ray monitor on the International Space Station (ISS), started observation in 2009 August. MAXI has two major objectives, 1) to issue rapid alerts of new X-ray novae/transients into astronomers worldwide and 2) to acquire long-term all-sky X-ray data. Thanks to the good network connection between the ISS and the ground station, we can obtain 70% of MAXI data through the real-time communication path. We built a ground system (referred as "MAXI-DB") to handle real-time data efficiently; with the MAXI-DB and the alert system we issued 29150 rapid alerts in the three years since MAXI started observation. It is crucial to provide MAXI data to scientists all over the world, because MAXI data includes rich information. The MAXI data has been released to public step by step. Daily data products including images, light curves and energy spectra for 29300 pre-registered X-ray sources have been archived on the MAXI web site (http://maxi.riken.jp/top). Since the MAXI data taken by the slit-scan observation includes complex information on all-sky X-ray sources, it is not easy to collect data for a given source quickly on demand. We thus developed the MAXI on-demand archive system which sort all event data in orders of the sky region and the time. The new archive system is confirmed to process data for any celestial source 29100 times faster than the former system.
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JAXA research and development report, 12 19-27, Mar, 2013Explosive growth of data volume in scientific domains has caused demand of machine processing of the massive scientific data. In this paper we propose several schemes of similarity search over astronomical X-ray data for X-ray outbursts. Specifically, we first detect outbursts from the original data, followed by smoothing for reducing noise and normalization. Having detected outburst patterns, we apply dynamic time warping (DTW), which is known to be robust against time scaling to evaluate similarities between two outburst patterns.We propose several variations based on DTW by taking features of the outburst patterns and requirements for the similarity search;we apply derivative DTW, which is a variant of DTW, and apply sliding windows to evaluate partial similarities. We evaluate feasibility of the proposed schemes by experiments using real X-ray astronomy data.
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JAXA research and development report, 12 9-18, Mar, 2013We have been working on methods of visualizing space science data. For the purpose of education and public outreach,devices built on mobile computing platforms (iOS and Android, etc.) are fascinating ones to represent space science data. While mobile devices require a large amount of computing resources to visualize science data, wireless data services for mobile devices are not yet fast enough to instantly transfer the sufficient amount of data. This paper introduces a method to progressively download science data in order to reduce the latency. The proposed method here is also expected to reduce memory usage and CPU usage in comparison with conventional space science data I/O libraries.
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全国大会講演論文集, 2012(1) 633-635, Mar 6, 2012近年の科学分野で扱われるデータの量は膨大である.その筆頭が天文学であり,今も多くのデータが蓄積されている.その内,現在注目されているものの一つに X線天体がある.動的タイムワーピング(Dynamic Time Warping,以下「DTW」)とは,音声や株価といった時系列データを比較する際よく用いられる手法である.これを利用するとDTW距離という類似度を示す一つの数値が得られる.本研究では,全天X線監視装置「MAXI」から提供されるX線天体観測データを対象に,X線天体が起こすバースト現象のデータに対しDTWを用いた類似検索を行い,類似したパターンを示す天体を発見する手法を提案する.
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第74回全国大会講演論文集, 2012(1) 633-634, Mar 6, 2012近年の科学分野で扱われるデータの量は膨大である．その筆頭が天文学であり，今も多くのデータが蓄積されている．その内，現在注目されているものの一つに X線天体がある．動的タイムワーピング(Dynamic Time Warping，以下「DTW」)とは，音声や株価といった時系列データを比較する際よく用いられる手法である．これを利用するとDTW距離という類似度を示す一つの数値が得られる．本研究では，全天X線監視装置「MAXI」から提供されるX線天体観測データを対象に，X線天体が起こすバースト現象のデータに対しDTWを用いた類似検索を行い，類似したパターンを示す天体を発見する手法を提案する．
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JAXA research and development report, 11 47-56, Mar, 2012With the advance of digital technologies, huge amounts of astronomical data are being produced today by ground-based observatories and astronomical satellites. In order to efficiently extract scientific information from these data, a convenient method to visualize a large amount of astronomical data is required. Meanwhile, recent digital planetarium technologies allow us to display high resolution images on a planetarium dome. Thus, in this paper, we have investigated possibilities to use digital planetarium as a tool to visualize a large amount of astronomical data. We have made a digital planetarium program using actual astronomical observation data, mainly from JAXA's scientific satellites. Such a planetarium program also can provide educational, public outreach and entertainment purposes.
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JAXA research and development report, 11(11-007) 7-11, Mar, 2012We report on current status of the Astronomical Data Sonification Project. We have sonified astronomical data sets, including data from X-ray pulsars, Geo-magnetic Kp indices, etc. and have published these results. We also developed a sound-based, interactive, data-plotting program. This software enables the visually impaired to turn astronomical data into meaningful sounds. In this paper we summarize the progress of the project and also discuss future plans.
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JAXA research and development report, 11(11-007) 13-22, Mar, 2012For the purpose of education and public outreach, this paper introduces methods of visualization and sonification of space science data in a time sequence. The data used in this paper are as follows: Observation data and orbital elements of X-ray astronomy satellites ASCA and Suzaku, PWS data observed by the aurora observation satellite AKEBONO, Geomagnetic Kp indices. X-ray observation data contains the attributes (position, time, pulse-height) of each X-ray events detected. In conjunction with the visualization of orbital elements of the satellite, it is possible to virtually experience the observation by means of visualization and sonification of the data. Also it is possible to hear the radio wave around the earth and geomagnetic variations by means of sonification of corresponding data. We used different method for sonification of the PWS data (wide-band distribution of radio waves) and that of Kp indices (described as musical diagrams).
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Proceedings of SPIE - The International Society for Optical Engineering, 8443, 2012
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Journal of health sciences, Nihon Fukushi University, 14 1-9, Mar 30, 2011We are developing a sound-based, interactive, data-plotting program to enable the visually impaired to turn astronomical data into meaningful sounds. The sonification software, called "splot", would be available to any scientist to analyze data. Splot reads ASCII data files containing various plotting commands and other data, and then outputs sounds corresponding to the data instead of plotting to a display or a printer. Input data for splot is partially compatible with "qdp", a data-plotting program developed by NASA HEASARC. In this paper, we report the status of development. In the current version, splot only sonifies a one-dimensional histogram and thus remains an experimental production. Before releasing this software, we must extend its functions for a suitable field test and construct a data-analysis environment for the visually impaired.
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ASTRONOMY & ASTROPHYSICS, 520, Sep, 2010
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Jun 28, 2010We report the detection of a time variable OVII line emission in a deep 100<br /> ks Suzaku X-ray Imaging Spectrometer spectrum of the Galactic Ridge X-ray<br /> emission. The observed line intensity is too strong (11+/-2 line unit or photon<br /> cm^-2 s^-1 str^-1) to be emitted inside the heavily obscured Galactic disk. It<br /> showed a factor of two time variation which shows a significant (~4 sigma)<br /> correlation with the solar wind O^7+ ion flux. The high line intensity and the<br /> good time correlation with the solar wind strongly suggests that it originated<br /> from geocoronal solar wind charge exchange emission. We discuss the X-ray line<br /> intensity considering a line of sight direction and also theoretical<br /> distribution models of the neutral hydrogen and solar wind around the Earth.<br /> Our results indicate that X-ray observationsof geocoronal solar wind charge<br /> exchange emission can be used to constrain these models.
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The astronomical herald, 103(7) 445-456, Jun 20, 2010
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Oct 2, 2008In order to elucidate origin of the Galactic Ridge X-ray Emission, we<br /> analyzed Suzaku data taken at various regions along the Galactic plane and<br /> studied their Fe-K emission line features. Suzaku resolved the Fe line complex<br /> into three narrow lines at ~6.4 keV,~6.7 keV and ~6.97 keV, which are K-lines<br /> from neutral (or low-ionized), He-like, and H-like iron ions, respectively. The<br /> 6.7 keV line is clearly seen in all the observed regions and its longitudinal<br /> distribution is consistent with that determined from previous observations. The<br /> 6.4 keV emission line was also found in various Galactic plane regions (b~0).<br /> Differences in flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines<br /> between the Galactic plane and the Galactic center regions are studied and its<br /> implication is discussed.
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Butsuri, 63(9) 670-677, Sep 5, 2008In space astronomy, most observation data are publicly released after short proprietary periods. Much more scientific results are expected from scientific satellites by opening the data toward scientists all over the world and archiving the data permanently, than otherwise. To that end, space organizations in many countries are developing public space-science data archives, which may be considered precious scientific legacies of the mankind. Space-science data has a characteristic that its use does not conflict with ethics or economic interests. Taking this characteristic positively, promoting the international sharing of the space-science data may enhance mutual understanding between the countries. Consequently, "Security by Science" may be achieved.
Presentations
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第1回 SPARC Japan セミナー2020 「研究データ公開：フルオープンと制限公開の境界線」, Oct 2, 2020 Invited
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JpGU-AGU Joint Meeting 2020:Virtual ユニオンセッション U-12 「地球惑星科学の進むべき道10 ビッグデータとオープンサイエンス」, Jul 15, 2020 Invited
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20 Years of Chandra Science Symposium
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The 29th annual international Astronomical Data Analysis Software & Systems (ADASS)
Professional Memberships
1Research Projects
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科学研究費助成事業, 日本学術振興会, Apr, 2024 - Mar, 2027
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, Apr, 2016 - Mar, 2019
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, 2009 - 2011
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Japan Society for the Promotion of Science, 2007 - 2009
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Grants-in-Aid for Scientific Research Grant-in-Aid for international Scientific Research, Japan Society for the Promotion of Science, 1992 - 1994
