Profile Information
- Affiliation
- Assistant professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration AgencyAssistant professor, Space and Astronautical Science program, The Graduate University for Advanced Studies
- Degree
- Ph. D.(Mar, 1998, Kyoto University)master's degree(Mar, 1995, Kyoto University)
- Researcher number
- 80342624
- ORCID ID
https://orcid.org/0000-0002-9099-5755- J-GLOBAL ID
- 202001011170717781
- researchmap Member ID
- R000011919
Papers
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Monthly Notices of the Royal Astronomical Society: Letters, 540(1) L34-L40, Mar 19, 2025ABSTRACT We report measurements of the linear polarization degree (PD) and angle (PA) for hard X-ray emission from the Crab pulsar and wind nebula. Measurements were made with the XL-Calibur ($\sim$15–80 keV) balloon-borne Compton-scattering polarimeter in July 2024. The polarization parameters are determined using a Bayesian analysis of Stokes parameters obtained from X-ray scattering angles. Well-constrained ($\sim 8.5\sigma$) results are obtained for the polarization of the $\sim$19–64 keV signal integrated over all pulsar phases: PD = (25.1$\pm$2.9) per cent and PA = (129.8$\pm 3.2)^\circ$. In the off-pulse (nebula-dominated) phase range, the PD is constrained at $\sim 4.5\sigma$ and is compatible with the phase-integrated result. The PA of the nebular hard X-ray emission aligns with that measured by IXPE in the 2–8 keV band for the toroidal inner region of the pulsar wind nebula, where the hard X-rays predominantly originate. For the main pulsar peak, PD = (32.8$^{+18.2}_{-28.5}$) per cent and PA = (156.0 $\pm$ 21.7)$^\circ$, while for the second peak (inter-pulse), PD = (0.0$^{+33.6}_{-0.0}$) per cent and PA = (154.5 $\pm$ 34.5)$^\circ$. A low level of polarization in the pulsar peaks likely does not favour emission originating from the inner regions of the pulsar magnetosphere. Discriminating between Crab pulsar emission models will require deeper observations, e.g. with a satellite-borne hard X-ray polarimeter.
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Nature, 638(8050) 365-369, Feb 12, 2025 Peer-reviewed
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Publications of the Astronomical Society of Japan, 77(1) L1-L8, Dec 26, 2024 Peer-reviewedAbstract 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.
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The Astrophysical Journal Letters, 977(2) L34-L34, Dec 11, 2024 Peer-reviewedAbstract The X-ray binary system Cygnus X-3 (4U 2030+40, V1521 Cyg) is luminous but enigmatic owing to the high intervening absorption. High-resolution X-ray spectroscopy uniquely probes the dynamics of the photoionized gas in the system. In this Letter, we report on an observation of Cyg X-3 with the XRISM/Resolve spectrometer, which provides unprecedented spectral resolution and sensitivity in the 2–10 keV band. We detect multiple kinematic and ionization components in absorption and emission whose superposition leads to complex line profiles, including strong P Cygni profiles on resonance lines. The prominent Fe xxv Heα and Fe xxvi Lyα emission complexes are clearly resolved into their characteristic fine-structure transitions. Self-consistent photoionization modeling allows us to disentangle the absorption and emission components and measure the Doppler velocity of these components as a function of binary orbital phase. We find a significantly higher velocity amplitude for the emission lines than for the absorption lines. The absorption lines generally appear blueshifted by ∼−500–600 km s−1. We show that the wind decomposes naturally into a relatively smooth and large-scale component, perhaps associated with the background wind itself, plus a turbulent, denser structure located close to the compact object in its orbit.
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Publications of the Astronomical Society of Japan, 76(6) 1186-1201, Oct 10, 2024 Peer-reviewedAbstract We present an initial analysis of the X-Ray Imaging and Spectroscopy Mission (XRISM) first-light observation of the supernova remnant (SNR) N 132D in the Large Magellanic Cloud. The Resolve microcalorimeter has obtained the first high-resolution spectrum in the 1.6–10 keV band, which contains K-shell emission lines of Si, S, Ar, Ca, and Fe. We find that the Si and S lines are relatively narrow, with a broadening represented by a Gaussian-like velocity dispersion of $\sigma _v \sim 450$ km s$^{-1}$. However, the Fe He$\alpha$ lines are substantially broadened with $\sigma _v \sim 1670$ km s$^{-1}$. This broadening can be explained by a combination of the thermal Doppler effect due to the high ion temperature and the kinematic Doppler effect due to the SNR expansion. Assuming that the Fe He$\alpha$ emission originates predominantly from the supernova ejecta, we estimate the reverse shock velocity at the time when the bulk of the Fe ejecta were shock heated to be $-1000 \lesssim V_{\rm rs}$ (km s$^{-1}$) $\lesssim 3300$ (in the observer frame). We also find that Fe Ly$\alpha$ emission is redshifted with a bulk velocity of $\sim 890$ km s$^{-1}$, substantially larger than the radial velocity of the local interstellar medium surrounding N 132D. These results demonstrate that high-resolution X-ray spectroscopy is capable of providing constraints on the evolutionary stage, geometry, and velocity distribution of SNRs.
Misc.
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日本物理学会講演概要集(CD-ROM), 78(2), 2023
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大気球シンポジウム: 2022年度 = Balloon Symposium: 2022, Nov, 2022大気球シンポジウム 2022年度（2022年11月7-8日. ハイブリッド開催（JAXA相模原キャンパス& オンライン)) Balloon Symposium 2022 (November 7-8, 2022. Hybrid(in-person & online) Conference (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 87名 資料番号: SA6000177030 レポート番号: isas22-sbs-030
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日本物理学会講演概要集(CD-ROM), 75(1), 2020
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日本物理学会講演概要集(CD-ROM), 75(2), 2020
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第32回宇宙構造・材料シンポジウム：講演集録 = Proceedings of 32nd Symposium on Aerospace Structure and Materials, Dec, 2016第32回宇宙構造・材料シンポジウム（2016年12月9日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)), 相模原市, 神奈川県資料番号: SA6000087012レポート番号: A11
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Acta Polytechnica, 53(1) 803-806, 2013A review of the Astro-H mission is presented here on behalf of the Astro-H collaboration. The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). One of the main uniquenesses of the ASTRO-H satellite is the high sensitivity and imaging capability of the wide energy band from 0.3 keV to 600 keV. The coverage is achieved by combining the four instruments of the SXS, SXI, HXI, and SGD. The other main uniqueness is a spectroscopic capability not only for a point-like source but also for an extended source with high spectral resolution of ΔE~4÷7eV of SXS. Using the unique powers of these instruments, ASTRO-H will address unresolved issues in high-energy astrophysics. © Czech Technical University in Prague, 2013.
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Dynamics & Design Conference, 2011 "706-1"-"706-8", Sep 5, 2011In the present paper, vibration properties of mirror foils installed in a hard X-ray telescope (HXT) on-board a satellite were investigated. Vibration tests and FEM analysis of mirror foils installed in the part model of HXT were conducted. From the experimental results, it appeared that the mirror had resonant frequencies at 64, 73 and 11 OHz. The modal shapes of 64 and 73Hz showed that the maximum amplitude appeared at edges of the foil. On the other hand, vibration amplitude became maximum at the center in the modal shape of 11 OHz. Experimental results of frequency responses of these modes agreed well with analytical results except around 64Hz. It is considered that the resonant mode of 64Hz was strongly affected by nonlinear characteristics of friction constraint between the foils and HXT housing.
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Journal of the Physical Society of Japan, 78 133-137, Jun 16, 2009We assume that the energy source in the Galactic Center is the black hole Sgr A, which becomes active when a star is captured in a rate of ∼ 10-5yr-1. During the active phase relativistic protons with a characteristic energy ∼ 6 x 1052erg per capture are ejected. We suppose that the annihilation of secondary positrons produced by proton-proton collisions is observed as the 511 keV line flux from the Galactic bulge. Though these positron are generated with relatively high energies (> 30 MeV), our model satisfy the criterion derived by Beacom and Yiiksel based on the COMPTEL data in the range 1-30 MeV. From our estimations it follows also that a flux of gamma-ray de-excitation lines ∼ 2.5 x 10-5 ph cm-2 s-1 in the range below 8 MeV is produced by the relativistic protons in the Galactic center. A specific line is the one at 1.809 MeV from radioactivity of 26 Al. The predicted quasi-stationary flux of the 26Al 1.809 MeV line from the 1° x 1 central region is < 10-6 ph cm-2 s-1. We conclude also the the thermal 6.5 keV X-ray flux and the non-thermal hard X-ray flux in the range 14-40 keV observed by SUZAKU is emitted by subrelativistic protons produced by accretion processes. © 2009 The Physical Society of Japan.
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2008 IEEE/LEOS INTERNATIONAL CONFERENCE ON OPTICAL MEMS AND NANOPHOTONICS, 104-105, 2008 Peer-reviewedX-ray reflectivity of an ultra light-weight X-ray optic using MEMS technologies was measured in two different energies (0.28 keV and 1.49 keV). The obtained reflectivities can be understood by considering the mirror surface structures.
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Meeting abstracts of the Physical Society of Japan, 62(2) 116-116, Aug 21, 2007
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Publications of the Astronomical Society of Japan, 57(1) 245-257, Feb 25, 2005<jats:title>Abstract</jats:title> <jats:p>We present the design and fabrication of the pre-collimator for the X-ray telescope onboard the X-ray astronomy satellite Astro-E2, and its effect on stray-light reduction. The pre-collimator was designed to efficiently reduce secondary reflection, which is the brightest component of stray light, giving rise to a ghost image in the field of view of the focal-plane detector. With the pre-collimator, composed of blades with an effective height of 30 mm, we confirmed from X-ray measurements that the intensity of the secondary reflection is reduced by roughly a few orders of magnitude on average in the off-axis angle range of $20' \hbox{--} 70'$. We also confirmed that the loss of the on-axis effective area due to installation of the pre-collimator is only $0.5 \pm 0.2\%$. The field of view becomes narrower, but the reduction factor amounts only to 8%. Ray-tracing simulations of in-flight observations also demonstrate that introduction of the pre-collimator is expected to be highly significant for improving data quality, due to a reduction of secondary reflection.</jats:p>
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ASTRONOMISCHE NACHRICHTEN, 324(1-2) 158-158, 2003We have carried out a deep X-ray observation on a typical Galactic plane<br /> region with the Chandra ACIS-I instrument with unprecedented sensitivity and<br /> spatial resolution, and detected 274 unidentified X-ray point sources in the<br /> \~500 arcmin2 region. In order to identify these new X-ray sources, we have<br /> carried out a near infrared follow-up observation using ESO/NTT infrared camera<br /> on 2002/7/28 and 2002/7/29. Initial results are briefly reported.
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Astrophysical Journal, Supplement Series, 138(1) 19-34, Jan 1, 2002The ASCA satellite made 107 pointing observations on a 5 × 5 deg 2 region around the center of our Galaxy from 1993 to 1999. In the X-ray images of the 0.7-3 keV or 3-10 keV bands, we found 52 point sources and a dozen diffuse sources. All the point sources are uniformly fitted with an absorbed power-law model. For selected bright sources, Sgr A*, AX J1745.6-2901, A1742-294, SLX 1744-300, GRO J1744-28, SLX 1737-282, GRS 1734-292, AX J1749.2-2725, KS 1741-293, GRS 1741.9-2853, and an unusual flare source XTE J1739-302, we present further detailed spectral and timing analyses and discuss their nature. The dozen extended X-ray sources comprise radio supernova remnants, giant molecular clouds, and some new discoveries. Most show emission lines from either highly ionized atoms or low-ionized irons. The X-ray spectra were fitted with either a thin thermal or power-law model. This paper summarizes the results and provides the ASCA X-ray source catalog in the Galactic center region.
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SCIENCE, 293(5535) 1633-1635, Aug, 2001The Galactic plane is a strong emitter of hard x-rays (2 to 10 kiloelectron volts), and the emission forms a narrow continuous ridge. The currently known hard x-ray sources are far too few to explain the ridge x-ray emission, and the fundamental question of whether the ridge emission is ultimately resolved into numerous dimmer discrete sources or truly diffuse emission has not yet been settled. In order to obtain a decisive answer, using the Chandra X-ray Observatory, we carried out the deepest hard x-ray survey of a Galactic plane region that is devoid of known x-ray point sources. We detected at least 36 new hard x-ray point sources in addition to strong diffuse emission within a 17' by 17' field of view. The surface density of the point sources is comparable to that at high Galactic latitudes after the effects of Galactic absorption are considered. Therefore, most of these point sources are probably extragalactic, presumably active galaxies seen through the Galactic disk. The Galactic ridge hard x-ray emission is diffuse, which indicates omnipresence within the Galactic plane of a hot plasma, the energy density of which is more than one order of magnitude higher than any other substance in the interstellar space.
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NEW CENTURY OF X-RAY ASTRONOMY, 251 310-311, 2001We present a Chandra observation of the giant molecular cloud Sgr B2 at the Galactic center region. We detected diffuse X-ray emission and 17 point sources in the cloud. The diffuse emission shows a strong 6.4 keV line from neutral iron, and is prominent on the Galactic center side. These features support the "X-ray Reflection Nebula" hypothesis, in which the cloud is irradiated by an external X-ray source in the direction of the Galactic center and emits fluorescent and scattered X-rays.
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NEW CENTURY OF X-RAY ASTRONOMY, 251 314-315, 2001Front the ASCA X-ray point-source list in the Galactic center 5 x 5 degree(2) region, we found the clear correlation between the position of the sources and the absorption. This fact implies that the major part of the absorption is due to the cold interstellar matter (ISM) in the line of sight. Using the correlation, we estimate the distribution of the cold ISM. We also found that the ratio of numbers of high mass binaries to low mass binaries is significantly smaller than that in the whole Galaxy or SMC, which implies that the past starburst activity in the Galactic center region was rather quiet.
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Publications of the Astronomical Society of Japan, 52(6) 1141-1145, Dec 1, 2000<jats:p>We report the discovery of an X-ray pulsar, AX J1740.1–2847, from the Galactic center region. This source was found as a faint hard X-ray object on 1998 September 7–8 with the ASCA Galactic center survey observation. Then, coherent pulsations of P = 729± 14 s period were detected. The X-ray spectrum is described by a flat power-law of ∼ 0.7 photon index. The large absorption column of log NH ∼ 22.4 cm−2 indicates that AX J1740.1–2847 is a distant source, larger than 2.4 kpc, and possibly near to the Galactic center region. The luminosity in the 2–10 keV band is larger than 2.5×1033 erg s−1, or likely to be 3.2×1034 erg s−1 at the Galactic-center distance. Although the slow-pulse period does not discriminate whether AX J1740.1–2847 is a white dwarf or neutron-star binary, the flat power-law and moderate luminosity strongly favor a neutron-star binary.</jats:p>
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Publications of the Astronomical Society of Japan, 52(4) L25-L30, Aug 25, 2000<jats:p>The X-ray spectrum in a 1° × 1° region of the Galactic center observed with the ASCA satellite is examined in detail, following the first report by Koyama et al. (1996, AAA 65.155.208). The observed spectrum contains prominent emission lines from helium-like and hydrogen-like ions of various elements, and is essentially the same all over the region. If the observed spectrum is thermal emission from hot plasmas, it requires multi-temperature plasma components, each at a different degree of ionization and with a different amount of absorption. The absence of adiabatic cooling and of systematic changes in the degree of ionization over the region is against the Galactic center origin of hot plasmas. A significant broadening of the helium-like and hydrogen-like iron K-lines is confirmed. The line width corresponds to a rms velocity of ∼ 3300 km s−1, which far exceeds the sound velocity in a plasma of kT ∼ 14 keV measured with the Ginga satellite. These facts cast doubt on a thermal origin of the observed X-ray emission.</jats:p>
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES, 25(3-4) 579-582, 2000We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a strong emission line at 6.4 keV, a low energy cutoff below 4 keV and a pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak position is shifted in the direction of the Galactic center by about 1-2 arcminute from the core of the molecular cloud. The X-ray spectrum and morphology are well reproduced by a scenario that X-rays from a source located at the Galactic center side are scattered by the molecular cloud Sgr B2, and come into our line of sight. Thus Sgr B2 may be called an X-ray reflection nebula. (C) 2000 COSPAR. Published by Elsevier Science Ltd.
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BROAD BAND X-RAY SPECTRA OF COSMIC SOURCES, 25(3-4) 391-394, 2000The ASCA results of the bursting X-ray pulsar GRO J1744-28 are reported. The observations were made twice, in February 1996 and March 1997. We detected 12 and 17 Type II bursts during the two observations, with mean bursting intervals of about 27 min and 37 min. Each burst is followed by an intensity dip with the depleted flux depending on the burst fluence. The energy spectra are approximated by an absorbed power law with additional structure around 6-7 keV, which is most probably due to iron and maybe reproduced by the disk line model with additional broadening mechanism. The absorption column is constant ((5 - 6) x 10(22) cm(-2)), independent of the observation dates and emission phase (persistent, burst and dip). This means the source may be actually located near the galactic center (8.5kpc). (C) 2000 COSPAR. Published by Elsevier Science Ltd.
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ASTROPHYSICAL JOURNAL, 517(1) 436-448, May, 1999We report the ASCA results of the bursting X-ray pulsar GRO J1744-28, which was observed in 1996 February and 1997 March. The source flux in the 2-10 keV band was 2.0 x 10(-8) ergs s(-1) cm(2) in 1996 and 5.0 x 10(-9) ergs s(-1) cm2 in 1997. We detected 12 and 17 type II bursts during type two observations, with mean bursting intervals of about 27 min and 37 min. Each burst is followed by an intensity dip with the depleted flux depending on the burst fluence. The energy spectra are approximated by an absorbed power law with additional structure around 6-7 keV. The constant absorption column, (5-6) x 10(22) cm(-2), independent of the observation dates and emission phases (persistent, burst, and dir) is interpreted as an interstellar absorption. The source may be actually located near the Galactic center, at a distance of 8.5 kpc. The structure in the energy spectrum at 6 7 keV is most probably due to iron and may be reproduced by a disk line model with additional broadening mechanism.
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ASTRONOMISCHE NACHRICHTEN, 320(4-5) 330-330, 1999We present the preliminary results of the hard X-ray global mapping of the Galactic Center region with ASCA. Many point sources and diffuse structures are resolved more clearly than before in the 2-10 keV band. Iron line emission is also intensely distributed along the Galactic plane. It is interpreted that either high temperature plasma concentrates on the Plane, or the molecular clouds illuminated by external strong X-ray sources are densely distributed along the Plane, or possibly both mechanisms are important.
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Meeting abstracts of the Physical Society of Japan, 52(1) 82-82, Mar 17, 1997
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Publications of the Astronomical Society of Japan, 48(3) 417-423, Jun 25, 1996<jats:p>With ASCA, we found highly absorbed X-rays from the position of the bright transient source A1742–289 with a variable flux ranging from 8 × 10−12 to 4 × 10−11 erg s−1 cm−2 in the 3–10 keV band. We discovered an X-ray burst and eclipses from A1742–289, establishing that A1742–289 is an eclipsing low-mass X-ray binary. Using the black-body radius during an X-ray burst, we estimated the distance of A1742–289 to be about 10 kpc, or near to the galactic center. The burst peak flux was then found below the Eddington limit of a neutron star. Excess soft X-rays during the eclipse were detected, which are interpreted to be scattering by interstellar dust-grains. Since A1742–289 was found to be an X-ray emitter, even in the quiescent state with a moderate but variable flux, and since A1742–289 is lying only 1′.3 from the galactic center, previously reported X-ray fluxes of the galactic center (Sgr A*) with non-imaging instruments might have suffered due to possible contamination of A1742–289.</jats:p>
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Publications of the Astronomical Society of Japan, 48(2) 249-255, 1996<jats:p>Detailed X-ray images and spectra of the galactic-center region up to 10 keV were obtained with ASCA. Diffuse thermal-emission with distinct Kα lines from highly ionized ions of various elements has confirmed the presence of an extended high-temperature plasma. The fluorescent X-ray emission from cold iron atoms in molecular clouds was also found, possibly due to irradiation by X-rays from the center, which was bright in the past, but is presently dim. The results suggest that the galactic center exhibited intermittent activities with a time-averaged energy generation rate comparable to Seyfert nuclei, a class of active galactic nuclei.</jats:p>
Presentations
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Optics & Photonics Japan 2023, Nov 29, 2023 Invited
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44th COSPAR Scientific Assembly, 2022
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nuclear burning in massive stars – towards the formation of binary black holes –, Jul 28, 2021
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Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray, Dec 19, 2020
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The 15th Symposium of Japanese Research Community on X-ray Imaging Optics, Oct 26, 2019 Invited
Teaching Experience
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Sep, 2023 - Mar, 2024
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Apr, 2021 - Mar, 2022Space Science Review (The Graduate University for Advanced Studies)
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Oct, 2019 - Mar, 2020Space Science Review (The Graduate University for Advanced Studies)
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Oct, 2009 - Mar, 2010Applied Physics (Chuo University)
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Apr, 2009 - Sep, 2009Astrophysics (Chuo University)
Professional Memberships
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Jul, 1998 - Present
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Mar, 1998 - Present
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Jan, 1997 - Present
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Aug, 1993 - Present
Research Projects
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2023 - Mar, 2027
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Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science, Apr, 2022 - Mar, 2025
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Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Japan Society for the Promotion of Science, Apr, 2020 - Mar, 2023
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科学研究費助成事業 挑戦的研究(萌芽), 日本学術振興会, Jun, 2019 - Mar, 2022
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科学研究費助成事業 新学術領域研究(研究領域提案型), 日本学術振興会, Apr, 2013 - Mar, 2015
