Details of the Researcher

PHOTO

Wataru Ishizaki
Section
Frontier Research Institute for Interdisciplinary Sciences
Job title
Specially Appointed Research Fellow

Research History 2

  • 2021/03 - 2024/03
    Japan Society for the Promotion of Science　Yukawa Institute for Theoretical Physics, Kyoto University

  • 2019/04 - 2021/03
    Kyoto University　Yukawa Institute for Theoretical Physics Research Physics under Extreme Conditions

Education 2

  • The University of Tokyo　Graduate School of Science　Department of Physics

    2016/04 - 2019/03

  • The University of Tokyo　Graduate School of Science　Department of Physics

    2014/04 - 2016/03

Research Areas 2

  • Natural sciences / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics / Plasma physics

  • Natural sciences / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics / Theoretical High-Energy Astrophysics

Papers 12

  1. Resolving the Origin of the Unidentified TeV Source HESS J1626-490 as a Relic of the Ancient Cosmic-Ray Factory SNR G335.2+0.1

    Tomohiko Oka, Wataru Ishizaki, Masaki Mori, Hidetoshi Sano, Hiromasa Suzuki, Takaaki Tanaka

    The Astrophysical Journal　2025/08/20

    DOI： 10.3847/1538-4357/adec80 　

  2. Parametric decay instability of circularly polarized Alfvén waves in magnetically dominated plasma

    Wataru Ishizaki, Kunihito Ioka

    Physical Review E　2024/07/15

    DOI： 10.1103/PhysRevE.110.015205 　

  3. A Self-Regulated Stochastic Acceleration Model of Pulsar Wind Nebulae

    Shuta J Tanaka, Wataru Ishizaki

    Progress of Theoretical and Experimental Physics　2024/05/07

    DOI： 10.1093/ptep/ptae069 　

  4. Interpretation of the CALET Electron+Positron Spectrum by Astrophysical Sources

    Holger Motz, Oscar Adriani, Yosui Akaike, Katsuaki Asano, Yoichi Aaoka, Eugenio Berti, Gabriele Bigongiari, Walter Robert Binns, Massimo Bongi, Paolo Brogi, Alessandro Bruno, Nicholas Wade Cannady, Guide Castellini, Caterina Checchia, Walter Robert Cherry, Gianmaria Collazuol, Georgia A. de Nolfo, Ken Ebisawa, Anthony W. Ficklin, Hideyuki Fuke, Sandro Gonzi, T. Gregory Guzik, Thomas Hams, Kinya Hibino, Masakatsu Ichimura, Kunihito Ioka, Wataru Ishizaki, Martin H. Israel, Katsumasa Kasahara, Jun Kataoka, Ryuho Kataoka, Yusaku Katayose, Chihiro Kato, Norita Kawanaka, Yuta Kawakubo, Kenko Kobayashi, Kazunori Kohri, Henric S. Krawczynski, John F. Krizmanic, Paolo Maestro, Pier Simone Marrocchesi, Alberto Maria Messineo, Jason W. Mitchell, Shoko Miyake, Alexander Moiseev, Masaki Mori, Nicola Mori, Holger Martin Motz, Kazuoki Munakata, Satoshi Nakahira, Jun Nishimura, Shoji Okuno, Jonathan Ormes, Shunsuke OZAWA, Lorenzo Pacini, Paolo Pacini, Brian Flint Rauch, Ricciarini Ricciarini, Kazuhiro Sakai, Takanori Sakamoto, Makoto Sasaki, Yuki Shimizu, Atsushi Shiomi, Piero Spillantini, Francesco Stolzi, Satoshi Sugita, Arta Sulaj, Masato Takita, Tadahisa Tamura, Toshio Terasawa, Shoji Torii, Yoshiki Tsunesada, Yukio Uchihori, Elena Vannuccini, John P. Wefel, Kazutaka Yamaoka, Shohei Yanagita, Atsumasa Yoshida, Kenji Yoshida, Wolfgang V Zober

    Proceedings of 38th International Cosmic Ray Conference — PoS(ICRC2023)　2023/08/14

    Publisher: Sissa Medialab

    DOI： 10.22323/1.444.0067 　

  5. Detection of gamma-rays around SNR HB9 and its implications for the diffusive shock-acceleration history

    Tomohiko Oka, Wataru Ishizaki

    Publications of the Astronomical Society of Japan　2022/05/16

    Publisher: Oxford University Press ({OUP})

    DOI： 10.1093/pasj/psac024 　

    ISSN： 0004-6264 2053-051X

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    <jats:title>Abstract</jats:title> <jats:p>We analyze the GeV gamma-ray emission data from the vicinity of the supernova remnant (SNR) HB9 (G160.9+2.6) from the Fermi-LAT 12 yr observations to quantify the evolution of diffusive shock acceleration (DSA) in the SNR. In the vicinity of HB9, there are molecular clouds whose locations do not coincide with the SNR shell in the line of sight. We detect significant gamma-ray emissions above 1 GeV spatially coinciding with the two prominent cloud regions, as well as emission from the SNR shell, the latter of which is consistent with the results of previous studies. The energy spectrum above 1 GeV in each region is fitted with a simple power-law function of dN/dE ∝ E−Γ. The fitting result indicates harder spectra, with power-law indices of Γ = 1.84 ± 0.18 and 1.84 ± 0.14, than that at the SNR shell, with Γ = 2.55 ± 0.10. The observed spectra from the cloud regions are found to be consistent with the theoretically expected gamma-ray emissions originating in the protons that escaped from SNR HB9, where particles can be accelerated up to higher energies than those in the shell at present. The resultant diffusion coefficient in the vicinity of the SNR is comparable to that of the Galactic mean.</jats:p>

  6. A Comprehensive Study of the Spectral Variation and the Brightness Profile of Young Pulsar Wind Nebulae

    Chin-Ping Hu, Wataru Ishizaki, C.-Y. Ng, Shuta J. Tanaka, Y.-L. Mong

    The Astrophysical Journal　927　(1)　87-87　2022/03/01

    Publisher: American Astronomical Society

    DOI： 10.3847/1538-4357/ac4d2d 　

  7. Fallback Accretion Halted by R-process Heating in Neutron Star Mergers and Gamma-Ray Bursts

    Wataru Ishizaki, Kenta Kiuchi, Kunihito Ioka, Shinya Wanajo

    The Astrophysical Journal　2021/12/01

    DOI： 10.3847/1538-4357/ac23d9 　

  8. Fallback Accretion Model for the Years-to-decades X-Ray Counterpart to GW170817

    Wataru Ishizaki, Kunihito Ioka, Kenta Kiuchi

    The Astrophysical Journal Letters　2021/08/01

    DOI： 10.3847/2041-8213/ac1120 　

  9. Modeling of broadband spectra and radial profiles of emission of pulsar wind nebulae

    Wataru Ishizaki, Katsuaki Asano, Kyohei Kawaguchi

    Proceedings of Science　358　2019

    Publisher: Sissa Medialab Srl

    ISSN： 1824-8039

  10. Outflow and Emission Model of Pulsar Wind Nebulae with the Back Reaction of Particle Diffusion

    Wataru Ishizaki, Katsuaki Asano, Kyohei Kawaguchi

    The Astrophysical Journal　2018/11/10

    DOI： 10.3847/1538-4357/aae389 　

  11. Energy calibration of CALET onboard the International Space Station Peer-reviewed

    Y. Asaoka, Y. Akaike, Y. Komiya, R. Miyata, S. Torii, O. Adriani, K. Asano, M. G. Bagliesi, G. Bigongiari, W. R. Binns, S. Bonechi, M. Bongi, P. Brogi, J. H. Buckley, N. Cannady, G. Castellini, C. Checchia, M. L. Cherry, G. Collazuol, V. Di Felice, K. Ebisawa, H. Fuke, T. G. Guzik, T. Hams, M. Hareyama, N. Hasebe, K. Hibino, M. Ichimura, K. Ioka, W. Ishizaki, M. H. Israel, A. Javaid, K. Kasahara, J. Kataoka, R. Kataoka, Y. Katayose, C. Kato, N. Kawanaka, Y. Kawakubo, H. Kitamura, H. S. Krawczynski, J. F. Krizmanic, S. Kuramata, T. Lomtadze, P. Maestro, P. S. Marrocchesi, A. M. Messineo, J. W. Mitchell, S. Miyake, K. Mizutani, A. A. Moiseev, K. Mori, M. Mori, N. Mori, H. M. Motz, K. Munakata, H. Murakami, Y. E. Nakagawa, S. Nakahira, J. Nishimura, S. Okuno, J. F. Ormes, S. Ozawa, L. Pacini, F. Palma, P. Papini, A. V. Penacchioni, B. F. Rauch, S. Ricciarini, K. Sakai, T. Sakamoto, M. Sasaki, Y. Shimizu, A. Shiomi, R. Sparvoli, P. Spillantini, F. Stolzi, I. Takahashi, M. Takayanagi, M. Takita, T. Tamura, N. Tateyama, T. Terasawa, H. Tomida, Y. Tsunesada, Y. Uchihori, S. Ueno, E. Vannuccini, J. P. Wefel, K. Yamaoka, S. Yanagita, A. Yoshida, K. Yoshida, T. Yuda

    Astroparticle Physics　91　1-10　2017/05/01

    DOI： 10.1016/j.astropartphys.2017.03.002 　

    ISSN： 0927-6505

  12. Broadband Photon Spectrum and its Radial Profile of Pulsar Wind Nebulae

    Ishizaki, Wataru, Tanaka, Shuta J., Asano, Katsuaki, Terasawa, Toshio

    The Astrophysical Journal　2017/04

    DOI： 10.3847/1538-4357/aa679b 　

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    The observed radial profiles of the X-ray emission from pulsar wind nebulae (PWNe) have been claimed to contradict the standard 1D steady model. However, the 1D model has not been tested to simultaneously reproduce the volume-integrated spectrum and the radial profile of the surface brightness. We revisit the 1D steady model and apply it to PWNe 3C 58 and G21.5-0.9. We find that the parameters of the pulsar wind, the radius of the termination shock {r}{ { s } }, and magnetization σ greatly affect both the photon spectrum and radial profile of the emission. We have shown that the parameters constrained by the entire spectrum lead to an X-ray nebula smaller than the observed nebula. We have also tested the case that reproduces only the observations in X- and gamma-rays, ignoring the radio and optical components. In this case, there are parameter sets that reproduce both the spectrum and emission profile, but the advection time to the edge of the nebula becomes much smaller than the age. Our detailed discussion clarifies that the standard 1D steady model has severe difficulty to simultaneously reproduce both the volume-integrated spectrum and the surface brightness. This implies that the model should be improved by taking into account extra physical processes such as spatial diffusion of particles. Additionally, we calculate the surface brightness profile of the radio, optical, and TeV gamma-rays. The future observations in these wavelengths are also important to probe the spatial distributions of the relativistic plasma and the magnetic field of PWNe....

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Research Projects 2

  1. TeV多粒子宇宙物理学で迫る電子宇宙線の起源

    石崎 渉

    Offer Organization: 日本学術振興会

    System: 科学研究費助成事業

    Category: 若手研究

    Institution: 東北大学

    2026/04/01 - 2031/03/31

  2. 重力波天体の長時間活動と中心エンジンによる相対論的インフロー・アウトフロー

    石崎 渉

    Offer Organization: 日本学術振興会

    System: 科学研究費助成事業

    Category: 特別研究員奨励費

    Institution: 京都大学

    2023/03/08 - 2024/03/31

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    連星中性子星合体からの重力波GW170817に同期して発見されたkilonovaは、連星合体に伴う放出物質がr過程元素の崩壊熱によって加熱されていることを強く示唆する。連星中性子星合体のシミュレーションによると、放出物質の一部は依然として重力的に束縛されており、しかるのちに合体後の星に向かってfallback accretionしていく。本課題では、r-process元素による加熱がfallback accretionに与える影響を評価すべく、流体計算とその準解析的モデル化をおこなった。その結果、加熱によって質量降着が抑制されることを見出し、降着の抑制が顕著になるタイムスケールを幅広い加熱プロファイルについて求めることができる公式を得た。さらに、GW170817で示唆された年スケールX線光度曲線の超過成分に関する新たな説を提案した。連星中性子星からの放出物質の内、post-merger ejectaと呼ばれる、数秒から数十秒のタイムスケールで放出される物質の一部がfallback accretionすることによって形成される降着円盤が、X線の超過成分を説明しうることを示した。 加えて、連星中性子星合体・ガンマ線バーストのみならず高エネルギー天体物理学一般に重要な課題である強く磁化したプラズマ中のAlfven波の崩壊についての研究も行った。中性子星やブラックホールのようなコンパクト星の周囲に形成される磁気圏は、電磁場のエネルギー密度がプラズマの静止エネルギー密度を凌駕する相対論的磁化率を持ったプラズマであることが期待される。このようなプラズマ中でのAlfven波の安定性を線形解析の範囲で網羅的に調査した結果、(1)崩壊不安定性は相対論的な磁化を帯びたプラズマにおいても生じること、(2)磁化率が大きい極限で、崩壊不安定性が消失することを見出した。

Teaching Experience 3

  1. Science of Nature　Tohoku Gakuin University

  2. Workshop IVa　Konan University

  3. Fluid Mechanics II　Konan University