宇宙科学広報・普及主幹付

山口 弘悦

Hiroya Yamaguchi

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 准教授
学位
博士(理学)(2008年3月 京都大学)

研究者番号
00513467
J-GLOBAL ID
201801007525282778
researchmap会員ID
B000340695

外部リンク

主な研究テーマ・プロジェクト業務

Ia型超新星原子過程/X線分光学将来計画の成果最大化

下記の業績リストは不完全です。「論文」は主要論文のみ、「講演・口頭発表等」は最近の招待講演のみリストしています。

 

座右の銘

努力して運を待て(仁科芳雄) 努力を続けていれば運が向いた時に見逃さないって意味だと思う。運は誰にでも同じ頻度で巡ってくる。それに気づき活かせるかは本人の努力次第。

疑行無名、疑事無功(『戦国策』) 後から迷走しないように達成目標と実施計画を明確にすべしって意味だと思う。目的意識もなく仕事に取り掛かるから、行き当たりばったりになり良い成果が挙がらない。

人、城を頼らば、城、人を捨せん(織田信長) プロジェクトがあれば何とかなると考えていたらプロジェクトが頓挫したときに自力で起き上がれないって意味だと思う。この懸念は2016年に現実のものとなった。 


学歴

 3

論文

 44
  • Tomoya Kinugawa, Hiroki Takeda, Ataru Tanikawa, Hiroya Yamaguchi
    The Astrophysical Journal 938(1) 52-52 2022年10月1日  
    Abstract It is generally believed that Type Ia supernovae are thermonuclear explosions of carbon–oxygen white dwarfs (WDs). However, there is currently no consensus regarding the events leading to the explosion. A binary WD (WD–WD) merger is a possible progenitor of Type Ia supernovae. Space-based gravitational wave (GW) detectors with considerable sensitivity in the decihertz range such as the DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) can observe WD–WD mergers directly. Therefore, access to the decihertz band of GWs would enable multi-messenger observations of Type Ia supernovae to determine their progenitors and explosion mechanism. In this paper, we consider the event rate of WD–WD mergers and the minimum detection range to observe one WD–WD merger per year, using a nearby galaxy catalog and the relation between Ia supernovae and their host galaxies. Furthermore, we calculate DECIGO’s ability to localize WD–WD mergers and to determine the masses of binary mergers. We estimate that a decihertz GW observatory can detect GWs with amplitudes of h ∼ 10−20 [Hz−1/2] at 0.01–0.1 Hz, which is 1000 times higher than the detection limit of DECIGO. Assuming the progenitors of Ia supernovae are merging WD–WD (1 M and 0.8 M), DECIGO is expected to detect 6600 WD–WD mergers within z = 0.08, and identify the host galaxies of such WD–WD mergers within z ∼ 0.065 using GW detections alone.
  • H. Sano, H. Yamaguchi, M. Aruga, Y. Fukui, K. Tachihara, M. D. Filipović, G. Rowell
    The Astrophysical Journal 933(2) 157-157 2022年7月1日  
    Abstract We report new H i observations of the Type Ia supernova remnant (SNR) SN 1006 using the Australia Telescope Compact Array with an angular resolution of $4\buildrel{\,\prime}\over{.} 5\times 1\buildrel{\,\prime}\over{.} 4$ (∼2 pc at the assumed SNR distance of 2.2 kpc). We find an expanding gas motion in position–velocity diagrams of H i with an expansion velocity of ∼4 km s−1 and a mass of ∼1000 M. The spatial extent of the expanding shell is roughly the same as that of SN 1006. We here propose a hypothesis that SN 1006 exploded inside the wind-blown bubble formed by accretion winds from the progenitor system consisting of a white dwarf and a companion star, and then the forward shock has already reached the wind wall. This scenario is consistent with the single-degenerate model. We also derived the total energy of cosmic-ray protons Wp to be only ∼1.2–2.0 × 1047 erg by adopting the averaged interstellar proton density of ∼25 cm−3. The small value is compatible with the relation between the age and Wp of other gamma-ray SNRs with ages below ∼6 kyr. The Wp value in SN 1006 will possibly increase up to several 1049 erg in the next ∼5 kyr via the cosmic-ray diffusion into the H i wind shell.
  • Wataru B Iwakiri, Motoko Serino, Tatehiro Mihara, Liyi Gu, Hiroya Yamaguchi, Megumi Shidatsu, Kazuo Makishima
    Publications of the Astronomical Society of Japan 73(5) 1405-1417 2021年10月4日  査読有り
    Abstract We discover an unidentified strong emission feature in the X-ray spectrum of EXO 1745−248 obtained by RXTE at 40 hr after the peak of a superburst. The structure was centered at 6.6 keV and significantly broadened with a large equivalent width of 4.3 keV, corresponding to a line photon flux of 4.7 × 10−3 ph cm−2 s−1. The 3–20 keV spectrum was reproduced successfully by a power-law continuum with narrow and broad (2.7 keV in full width at half maximum) Gaussian emission components. Alternatively, the feature can be described by four narrow Gaussians, centered at 5.5 keV, 6.5 keV, 7.5 keV, and 8.6 keV. Considering the strength and shape of the feature, it is unlikely to have originated from reflection of the continuum X-rays by some optically thick material, such as an accretion disk. Moreover, the intensity of the emission structure decreased significantly with an exponential time scale of 1 hr. The feature was not detected in an INTEGRAL observation performed 10 hr before the RXTE observation with a line flux upper limit of 1.5 × 10−3 ph cm−2 s−1. The observed emission structure is consistent with gravitationally redshifted charge exchange emission from Ti, Cr, Fe, and Co. We suggest that the emission results from a charge exchange interaction between a highly metal-enriched fall-back ionized burst wind and an accretion disk, at a distance of ∼60 km from the neutron star. If this interpretation is correct, the results provide new information on nuclear burning processes during thermonuclear X-ray bursts.
  • Yuken Ohshiro, Hiroya Yamaguchi, Shing-Chi Leung, Ken’ichi Nomoto, Toshiki Sato, Takaaki Tanaka, Hiromichi Okon, Robert Fisher, Robert Petre, Brian J. Williams
    The Astrophysical Journal Letters 913(2) L34-L34 2021年6月1日  査読有り
    Abstract The supernova remnant (SNR) 3C 397 is thought to originate from a Type Ia supernova (SN Ia) explosion of a near-Chandrasekhar-mass (MCh) progenitor, based on the enhanced abundances of Mn and Ni revealed by previous X-ray study with Suzaku. Here we report follow-up XMM-Newton observations of this SNR, conducted with the aim of investigating the detailed spatial distribution of the Fe-peak elements. We have discovered an ejecta clump with extremely high abundances of Ti and Cr, in addition to Mn, Fe, and Ni, in the southern part of the SNR. The Fe mass of this ejecta clump is estimated to be ∼0.06 M, under the assumption of a typical Fe yield for SNe Ia (i.e., ∼0.8 M). The observed mass ratios among the Fe-peak elements and Ti require substantial neutronization that is achieved only in the innermost regions of a near-MCh SN Ia with a central density of ρc ∼ 5 × 109 g cm−3, significantly higher than typically assumed for standard near-MCh SNe Ia (ρc ∼ 2 × 109 g cm−3). The overproduction of the neutron-rich isotopes (e.g., 50Ti and 54Cr) is significant in such high-ρc SNe Ia, with respect to the solar composition. Therefore, if 3C 397 is a typical high-ρc near-MCh SN Ia remnant, the solar abundances of these isotopes could be reproduced by the mixture of the high- and low-ρc near-MCh and sub-MCh Type Ia events, with ≲20% being high-ρc near-MCh.
  • Hiroya Yamaguchi, Fabio Acero, Chuan-Jui Li, You-Hua Chu
    The Astrophysical Journal Letters 910(2) L24-L24 2021年4月1日  査読有り筆頭著者
    Abstract The geometric structure of supernova remnants (SNR) provides a clue to unveiling the pre-explosion evolution of their progenitors. Here we present an X-ray study of N103B (0509–68.7), a Type Ia SNR in the Large Magellanic Cloud, that is known to be interacting with dense circumstellar matter (CSM). Applying our novel method for feature extraction to deep Chandra observations, we have successfully resolved the CSM, Fe-rich ejecta, and intermediate-mass element (IME) ejecta components, and revealed each of their spatial distributions. Remarkably, the IME ejecta component exhibits a double-ring structure, implying that the SNR expands into an hourglass-shape cavity and thus forms bipolar bubbles of the ejecta. This interpretation is supported by more quantitative spectroscopy that reveals a clear bimodality in the distribution of the ionization state of the IME ejecta. These observational results can be naturally explained if the progenitor binary system had formed a dense CSM torus on the orbital plane prior to the explosion, providing further evidence that the SNR N103B originates from a single-degenerate progenitor.

MISC

 9

書籍等出版物

 1

講演・口頭発表等

 28

担当経験のある科目(授業)

 5

共同研究・競争的資金等の研究課題

 4

● 指導学生の顕著な論文

 1
  • 指導学生名
    大城 勇憲
    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)
    Ohshiro et al., ApJL 913, L34, 7 (2021)
    論文タイトル
    Discovery of a Highly Neutronized Ejecta Clump in the Type Ia Supernova Remnant 3C 397
    DOI
    https://doi.org/10.3847/2041-8213/abff5b

● 専任大学名

 1
  • 専任大学名
    東京大学(University of Tokyo)