Associate for Education and Public Outreach

Masahiro Tsujimoto

  (辻本 匡弘)

Profile Information

Affiliation
Assistant professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
准教授, 物理科学研究科 宇宙科学専攻, 国立大学法人総合研究大学院大学
Degree
博士(理学)(Mar, 2003, 京都大学)
修士(理学)(Mar, 2000, 京都大学)

Contact information
tsujimotastro.isas.jaxa.jp
Researcher number
10528178
ORCID ID
 https://orcid.org/0000-0002-9184-5556
J-GLOBAL ID
201801010256574610
Researcher ID
ABC-6667-2020
researchmap Member ID
B000296937

External link

Papers

 212
  • Miki Kurihara, Wataru Buz Iwakiri, Masahiro Tsujimoto, Ken Ebisawa, Shin Toriumi, Shinsuke Imada, Yohko Tsuboi, Kazuki Usui, Keith C. Gendreau, Zaven Arzoumanian
    The Astrophysical Journal, 965(2) 135-135, Apr 1, 2024  Peer-reviewed
    Abstract We detected a giant X-ray flare from the RS CVn–type binary star UX Ari using the Monitor of All-sky X-ray Image on 2020 August 17 and started a series of Neutron star Interior Composition Explorer observations 89 minutes later. For a week, the entire duration of the flare was covered with 32 snapshot observations including the rising phase. The X-ray luminosity reached 2 × 1033 erg s−1, and the entire energy release was ∼1038 erg in the 0.5–8.0 keV band. X-ray spectra characterized by continuum emission with lines of Fe xxv Heα and Fe xxvi Lyα were obtained. We found that the temperature peaks before the flux does, which suggests that the period of plasma formation in the magnetic flare loop was captured. Using the continuum information (temperature, flux, and their delay time), we estimated the flare loop size to be ∼3 × 1011 cm and the peak electron density to be ∼4 × 1010 cm−3. Furthermore, using the line ratio of Fe xxv and Fe xxvi, we investigated any potential indications of deviation from collisional ionization equilibrium (CIE). The X-ray spectra were consistent with CIE plasma throughout the flare, but the possibility of an ionizing plasma away from CIE was not rejected in the flux rising phase.
  • Masahiro Tsujimoto, Misaki Mizumoto, Ken Ebisawa, Hirokazu Odaka, Qazuya Wada
    Astrophysical Journal, 960(1), Jan 1, 2024  
    Supersoft X-ray sources (SSSs) are white dwarf (WD) binaries that radiate almost entirely below ∼1 keV. Their X-ray spectra are often complex when viewed with the X-ray grating spectrometers, where numerous emission and absorption features are intermingled and hard to separate. The absorption features are mostly from the WD atmosphere, for which radiative transfer models have been constructed. The emission features are from the corona surrounding the WD atmosphere, in which incident emission from the WD surface is reprocessed. Modeling the corona requires different solvers and assumptions for the radiative transfer, which has yet to be achieved. We chose CAL87, an SSS in the Large Magellanic Cloud, which exhibits emission-dominated spectra from the corona, as the WD atmosphere emission is assumed to be completely blocked by the accretion disk. We constructed a radiative transfer model for the corona using two radiative transfer codes: xstar for a one-dimensional two-stream solver and MONACO for a three-dimensional Monte Carlo solver. We identified their differences and limitations in comparison to the spectra taken with the Reflection Grating Spectrometer on board the XMM-Newton satellite. We finally obtained a sufficiently good spectral model of CAL87 based on the radiative transfer of the corona plus an additional collisionally ionized plasma. In the coming X-ray microcalorimeter era, it will be required to interpret spectra based on radiative transfer in a wider range of sources than what is presented here.
  • Mayu Tominaga, Masahiro Tsujimoto, Ken Ebisawa, Teruaki Enoto, Kimitake Hayasaki
    Astrophysical Journal, 958(1), Nov 1, 2023  
    Circinus X-1 (Cir X-1) is a neutron star binary with an elliptical orbit of 16.6 days. The source is unique for its extreme youth, providing a key to understanding early binary evolution. However, its X-ray variability is too complex to reach a clear interpretation. We conducted the first high-cadence (every 4 hr, on average) observations covering one entire orbit using the NICER X-ray telescope. The X-ray flux behavior can be divided into stable, dip, and flaring phases. The X-ray spectra in all phases can be described by a common model consisting of a partially covered disk blackbody emission and the line features from a highly ionized photoionized plasma. The spectral change over the orbit is attributable to rapid changes of the partial covering medium in the line of sight and gradual changes of the disk blackbody emission. Emission lines of H- and He-like Mg, Si, S, and Fe are detected, most prominently in the dip phase. The Fe emission lines change to absorption in the course of the transition from the dip phase to the flaring phase. The estimated ionization degree indicates no significant changes, suggesting that the photoionized plasma is stable over the orbit. We propose a simple model in which the disk blackbody emission is partially blocked by a local medium in the line of sight that has spatial structures depending on the azimuth of the accretion disk. Emission lines upon the continuum emission are from the photoionized plasma located outside of the blocking material.
  • R. Imamura, H. Awaki, M. Tsujimoto, S. Yamada, F. S. Porter, C. A. Kilbourne, R. L. Kelley, Y. Takei
    Journal of Low Temperature Physics, 211(5-6) 426-433, Jun, 2023  
    Low-temperature detectors often use mechanical coolers as part of the cooling chain in order to reach sub-Kelvin operating temperatures. The microphonic noise caused by the mechanical coolers is a general and inherent issue for these detectors. We have observed this effect in the ground test data obtained with the Resolve instrument to be flown on the XRISM satellite. Resolve is a cryogenic X-ray microcalorimeter spectrometer with a required energy resolution of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient temperature to ∼ 4 K: four two-stage Stirling coolers (STC) driven nominally at 15 Hz and a Joule–Thomson cooler (JTC) driven nominally at 52 Hz. In 2019, we operated the flight-model instrument for two weeks, in which we also obtained accelerometer data inside the cryostat at a low-temperature stage (He tank). X-ray detector and accelerometer data were obtained continuously while changing the JTC drive frequency, which produced a unique data set for investigating how the vibration from the cryocoolers propagates to the detector. In the detector noise spectra, we observed harmonics of both STCs and JTC. More interestingly, we also observed the low (< 20 Hz) frequency beat between the 4th JTC and 14th STC harmonics and the 7th JTC and the 23–24th STC harmonics. We present here a description and interpretation of these measurements.
  • Tomoki Omama, Masahiro Tsujimoto, Ken Ebisawa, Misaki Mizumoto
    Astrophysical Journal, 945(2), Mar 1, 2023  
    MAXI J1820+070 is a transient black hole binary discovered on 2018 March 11. The unprecedented rich statistics brought by the NICER X-ray telescope allow detailed timing analyses up to ∼1 kHz uncompromised by photon shot noise. To estimate the time lags, a Fourier analysis was applied, which led to two different conclusions for the system configuration: one supporting a lamp-post configuration with a stable accretion disk extending close to the innermost stable circular orbit and the other supporting a truncated accretion disk contracting with time. Using the same data set, we present the results based on the cross-correlation function (CCF). The CCF is calculated between two different X-ray bands where one side is subtracted from the other side, which we call the differential CCF (dCCF). Soft and hard lags of ∼0.03 and 3 s, respectively, are clearly identified without being diluted by the spectral mixture, demonstrating the effectiveness of the dCCF analysis. The evolution of these lags is tracked, along with spectral changes for the first 120 days since discovery. Both the dCCF and spectral fitting results are interpreted as the soft lag being a reverberation lag between the Comptonized emission and the soft excess emission, and that the hard lag is between the disk blackbody emission and the Comptonized emission. The evolutions of these lags are in line with the picture of a truncated disk contracting with time.

Misc.

 26
  • 植松令太, 石野宏和, 桜井雄基, 松村知岳, 高久諒太, HOANG Thuong, 辻本匡弘, 富永愛侑, 富永愛侑, MATSUDA F., 小栗秀悟
    日本物理学会講演概要集(CD-ROM), 78(2), 2023  
  • 堂谷忠靖, 関本裕太郎, 辻本匡弘, 小栗秀悟, 松田フレドリック, 永田竜, 篠崎慶亮, 小田切公秀, 綿貫一也, 高倉隼人, 富永愛侑, 中野遼, 増村亮, 羽澄昌史, DE HAAN Tijmen, 長谷川雅也, 長崎岳人, 加藤晶大, 片山伸彦, 松村知岳, 桜井雄基, 長谷部孝, GHIGNA Tommaso, 杉山真也, 高久諒太, 星野百合香, 石野宏和, STEVER Samantha, 小松国幹, 高瀬祐介, 長野佑哉, 鹿島伸悟, 小松英一郎
    日本天文学会年会講演予稿集, 2021, 2021  
  • 堂谷忠靖, 篠崎慶亮, 関本裕太郎, 高倉隼人, 辻本匡弘, 長谷部孝, 満田和久, 永田竜, 羽澄昌史, 南雄人, 片山伸彦, 桜井雄基, 菅井肇, 高倉理, 松村知岳, 石野宏和, 魚住聖, 鹿島伸悟, 小松英一郎
    日本天文学会年会講演予稿集, 2020, 2020  
  • 堂谷忠靖, 関本裕太郎, 篠崎慶亮, 辻本匡弘, 小栗秀悟, 長谷部孝, 永田竜, 羽澄昌史, 南雄人, 長谷川雅也, DE HAAN Tijmen, 長崎岳人, 片山伸彦, 松村知岳, 桜井雄基, 今田大皓, 石野宏和, STEVER Samantha Lynn, 鹿島伸悟, 小松英一郎
    宇宙科学技術連合講演会講演集(CD-ROM), 64th, 2020  
  • 関本裕太郎, 堂谷忠靖, 篠崎慶亮, 高倉隼人, 辻本匡弘, 長谷部孝, 満田和久, 永田竜, 羽澄昌史, 南雄人, 片山伸彦, 桜井雄基, 菅井肇, 高倉理, 松村知岳, 石野宏和, 魚住聖, 鹿島伸悟, 小松英一郎, 今田大皓
    日本天文学会年会講演予稿集, 2019, 2019  

Research Projects

 7