研究者業績
基本情報
- 所属
- 埼玉大学 大学院理工学研究科 理工学研究科 教授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 特任教授
- 学位
- 博士(2002年3月 東京大学)
- J-GLOBAL ID
- 200901062224980497
- researchmap会員ID
- 1000368169
- 外部リンク
研究キーワード
14経歴
7-
2025年4月 - 現在
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2025年4月 - 現在
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2018年4月 - 2025年3月
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2007年10月 - 2025年3月
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2003年10月 - 2007年9月
学歴
3-
1999年4月 - 2002年
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1997年4月 - 1999年3月
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1993年4月 - 1997年3月
委員歴
8-
2009年6月 - 現在
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2025年6月 - 2027年5月
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2025年4月 - 2027年3月
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2017年6月 - 2019年6月
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2013年4月 - 2019年4月
論文
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2024年4月XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source candidate XRISM J1911+0509 on 2024-04-12 TT. The source position is determined to be (R.A., Dec.) = (287.737 deg, 5.152 deg) with systematic error of ~ 50 arcsec....
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2024年3月XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source candidate XRISM J1628-4846 on 2024-03-30 TT. The source position is determined to be (R.A., Dec.) = (247.092 deg, -48.771 deg) with systematic error of ~ 1 arcmin....
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2024年3月XRISM/Xtend Transient Search (XTS) detected an X-ray flare from a new X-ray source candidate XRISM J0335+0025 at 2024-03-09 TT. The source position is determined to be (R.A., Dec.) = (53.897 deg, 0.422 deg) with a systematic uncertainty of ~ 40 arcsec....
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2024年3月XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray source candidate XRISM J1908+0659 on 2024-03-27 TT. The source position is determined to be (R.A., Dec.) = (287.089 deg, 6.976 deg) with a systematic uncertainty of 40 arcsec....
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The Astrophysical Journal 2024年1月1日 査読有りSupernova (SN) 1987A is one of the best candidates to exploit the capabilities of the freshly launched XRISM satellite. This celestial object offers the unique opportunity to study the evolution of an SN into a young supernova remnant. To date, the X-ray emission has been dominated by the shocked circumstellar medium, with no shocked ejecta firmly detected. However, recent studies provide compelling evidence that in the forthcoming years, the X-ray emission from SN 1987A will increasingly stem from the ejecta. Our aim is to assess the proficiency of the XRISM-Resolve high-resolution spectrometer in pinpointing signatures of the shocked ejecta in SN 1987A. Taking advantage of a self-consistent state-of-the-art magneto-hydrodynamic simulation that describes the evolution from SN 1987A to its remnant, we synthesized the XRISM-Resolve spectrum of SN 1987A, as it would be collected in the allocated observation during the performance verification phase, which is foreseen for 2024. Our predictions clearly show the leading role of shocked ejecta in shaping the profile of the emission lines. The Doppler broadening associated with the bulk motion along the line of sight of the rapidly expanding ejecta is shown to increase the line widths well above the values observed so far. The quantitative comparison between our synthetic spectra and the XRISM spectra will enable us to establish a strong connection between the broadened line emission and the freshly shocked ejecta. This, in turn, will allow us to retrieve the ejecta dynamics and chemical composition from the X-ray emission....
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Frontiers in Astronomy and Space Sciences 2023年12月 査読有りHEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10″ full width at half maximum) and broad spectral coverage (0.2–80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. HEX-P is ideally suited to address important problems in the physics and astrophysics of supernova remnants (SNRs) and pulsar wind nebulae (PWNe). For shell SNRs, HEX-P can greatly improve our understanding via more accurate spectral characterization and localization of non-thermal X-ray emission from both non-thermal-dominated SNRs and those containing both thermal and non-thermal components, and can discover previously unknown non-thermal components in SNRs. Multi-epoch HEX-P observations of several young SNRs (e.g., Cas A and Tycho) are expected to detect year-scale variabilities of X-ray filaments and knots, thus enabling us to determine fundamental parameters related to diffusive shock acceleration, such as local magnetic field strengths and maximum electron energies. For PWNe, HEX-P will provide spatially-resolved, broadband X-ray spectral data separately from their pulsar emission, allowing us to study how particle acceleration, cooling, and propagation operate in different evolution stages of PWNe. HEX-P is also poised to make unique and significant contributions to nuclear astrophysics of Galactic radioactive sources by improving detections of, or limits on, 44Ti in the youngest SNRs and by potentially discovering rare nuclear lines as evidence of double neutron star mergers. Throughout the paper, we present simulations of each class of objects, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of SNRs, PWNe, and nuclear astrophysics....
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Frontiers in Astronomy and Space Sciences 2023年12月 査読有りHEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10″ FWHM) and broad spectral coverage (0.2–80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. With the recent discoveries of over 40 ultra-high-energy gamma-ray sources (detected above 100 TeV) and neutrino emission in the Galactic Plane, we have entered a new era of multi-messenger astrophysics facing the exciting reality of Galactic PeVatrons. In the next decade, as more Galactic PeVatrons and TeV gamma-ray sources are expected to be discovered, the identification of their acceleration and emission mechanisms will be the most pressing issue in both particle and high-energy astrophysics. In this paper, along with its companion papers, we will present that HEX-P is uniquely suited to address important problems in various cosmic-ray accelerators, including Galactic PeVatrons, through investigating synchrotron X-ray emission of TeV–PeV electrons produced by both leptonic and hadronic processes. For Galactic PeVatron candidates and other TeV gamma-ray sources, HEX-P can fill in a large gap in the spectral-energy distributions (SEDs) of many objects observed in radio, soft X-rays, and gamma rays, constraining the maximum energies to which electrons can be accelerated, with implications for the nature of the Galactic PeVatrons and their contributions to the spectrum of Galactic cosmic rays beyond the knee at ∼3 PeV. In particular, X-ray observation with HEX-P and TeV observation with CTAO will provide the most powerful multi-messenger diagnostics to identify Galactic PeVatrons and explore a variety of astrophysical shock mechanisms. We present simulations of each class of Galactic TeV–PeV sources, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of Galactic cosmic-ray accelerators. In addition, we discuss HEX-P's unique and complementary roles to upcoming gamma-ray and neutrino observatories in the 2030s....
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Astronomy and Astrophysics 2023年12月 査読有り<BR /> Aims: Large-Sized Telescope 1 (LST-1), the prototype for the Large-Sized Telescope at the upcoming Cherenkov Telescope Array Observatory, is concluding its commissioning phase at the Observatorio del Roque de los Muchachos on the island of La Palma. The proximity of LST-1 to the two MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes makes it possible to carry out observations of the same gamma-ray events with both systems. <BR /> Methods: We describe the joint LST-1+MAGIC analysis pipeline and used simultaneous Crab Nebula observations and Monte Carlo simulations to assess the performance of the three-telescope system. The addition of the LST-1 telescope allows for the recovery of events in which one of the MAGIC images is too dim to survive analysis quality cuts. <BR /> Results: Thanks to the resulting increase in the collection area and stronger background rejection, we found a significant improvement in sensitivity, allowing for the detection of 30% weaker fluxes in the energy range between 200 GeV and 3 TeV. The spectrum of the Crab Nebula, reconstructed in the energy range between ~60 GeV and ~10 TeV, is in agreement with previous measurements....
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Astronomy and Astrophysics 2023年11月 査読有りWe present a novel approach to the determination of the pointing of Imaging Atmospheric Cherenkov Telescopes (IACTs) using the trajectories of the stars in their camera's field of view. The method starts with the reconstruction of the star positions from the Cherenkov camera data, taking into account the point spread function of the telescope, to achieve a satisfying reconstruction accuracy of the pointing position. A simultaneous fit of all reconstructed star trajectories is then performed with the orthogonal distance regression (ODR) method. ODR allows us to correctly include the star position uncertainties and use the time as an independent variable. Having the time as an independent variable in the fit makes it better suitable for various star trajectories. This method can be applied to any IACT and requires neither specific hardware nor interface or special data-taking mode. In this paper, we use the Large-Sized Telescope (LST) data to validate it as a useful tool to improve the determination of the pointing direction during regular data taking. The simulation studies show that the accuracy and precision of the method are comparable with the design requirements on the pointing accuracy of the LST (≤14″). With the typical LST event acquisition rate of 10 kHz, the method can achieve up to 50 Hz pointing monitoring rate, compared to 𝒪(1) Hz achievable with standard techniques. The application of the method to the LST prototype (LST-1) commissioning data shows the stable pointing performance of the telescope....
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The Astrophysical Journal 2023年10月 査読有りThe Cherenkov Telescope Array (CTA) is a next-generation ground-based observatory for gamma-ray astronomy at very high energies. The Large-Sized Telescope prototype (LST-1) is located at the CTA-North site, on the Canary Island of La Palma. LSTs are designed to provide optimal performance in the lowest part of the energy range covered by CTA, down to ≃20 GeV. LST-1 started performing astronomical observations in 2019 November, during its commissioning phase, and it has been taking data ever since. We present the first LST-1 observations of the Crab Nebula, the standard candle of very-high-energy gamma-ray astronomy, and use them, together with simulations, to assess the performance of the telescope. LST-1 has reached the expected performance during its commissioning period-only a minor adjustment of the preexisting simulations was needed to match the telescope's behavior. The energy threshold at trigger level is around 20 GeV, rising to ≃30 GeV after data analysis. Performance parameters depend strongly on energy, and on the strength of the gamma-ray selection cuts in the analysis: angular resolution ranges from 0.°12-0.°40, and energy resolution from 15%-50%. Flux sensitivity is around 1.1% of the Crab Nebula flux above 250 GeV for a 50 hr observation (12% for 30 minutes). The spectral energy distribution (in the 0.03-30 TeV range) and the light curve obtained for the Crab Nebula agree with previous measurements, considering statistical and systematic uncertainties. A clear periodic signal is also detected from the pulsar at the center of the Nebula....
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The Astrophysical Journal 2023年8月 査読有りGravitational redshift is a fundamental parameter that allows us to determine the mass-to-radius ratio of compact stellar objects, such as black holes, neutron stars, and white dwarfs (WDs). In the X-ray spectra of the close binary system, RX J1712.6-2414, obtained from the Chandra High Energy Transmission Grating observation, we detected significant redshifts for characteristic X-rays emitted from hydrogen-like magnesium, silicon (ΔE/E rest ~ 7 × 10-4), and sulfur (ΔE/E rest ~ 15 × 10-4) ions, which are over the instrumental absolute energy accuracy (ΔE/E rest ~ 3.3 × 10-4). Considering some possible factors, such as Doppler shifts associated with the plasma flow, systemic velocity, and optical depth, we concluded that the major contributor to the observed redshift is the gravitational redshift of the WD harbored in the binary system, which is the first gravitational redshift detection from a magnetic WD. Moreover, the gravitational redshift provides us with a new method of WD mass measurement by invoking the plasma-flow theory with strong magnetic fields in close binaries. Regardless of large uncertainty, our new method estimated the WD mass to be M WD > 0.9 M ⊙....
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Astronomy and Astrophysics 2023年5月 査読有りContext. Several new ultrahigh-energy (UHE) γ-ray sources have recently been discovered by the Large High Altitude Air Shower Observatory (LHAASO) collaboration. These represent a step forward in the search for the so-called Galactic PeVatrons, the enigmatic sources of the Galactic cosmic rays up to PeV energies. However, it has been shown that multi-TeV γ-ray emission does not necessarily prove the existence of a hadronic accelerator in the source; indeed this emission could also be explained as inverse Compton scattering from electrons in a radiation-dominated environment. A clear distinction between the two major emission mechanisms would only be made possible by taking into account multi-wavelength data and detailed morphology of the source. <BR /> Aims: We aim to understand the nature of the unidentified source LHAASO J2108+5157, which is one of the few known UHE sources with no very high-energy (VHE) counterpart. <BR /> Methods: We observed LHAASO J2108+5157 in the X-ray band with XMM-Newton in 2021 for a total of 3.8 hours and at TeV energies with the Large-Sized Telescope prototype (LST-1), yielding 49 hours of good-quality data. In addition, we analyzed 12 years of Fermi-LAT data, to better constrain emission of its high-energy (HE) counterpart 4FGL J2108.0+5155. We used naima and jetset software packages to examine the leptonic and hadronic scenario of the multi-wavelength emission of the source. <BR /> Results: We found an excess (3.7σ) in the LST-1 data at energies E > 3 TeV. Further analysis of the whole LST-1 energy range, assuming a point-like source, resulted in a hint (2.2σ) of hard emission, which can be described with a single power law with a photon index of Γ = 1.6 ± 0.2 the range of 0.3 − 100 TeV. We did not find any significant extended emission that could be related to a supernova remnant (SNR) or pulsar wind nebula (PWN) in the XMM-Newton data, which puts strong constraints on possible synchrotron emission of relativistic electrons. We revealed a new potential hard source in Fermi-LAT data with a significance of 4σ and a photon index of Γ = 1.9 ± 0.2, which is not spatially correlated with LHAASO J2108+5157, but including it in the source model we were able to improve spectral representation of the HE counterpart 4FGL J2108.0+5155. <BR /> Conclusions: The LST-1 and LHAASO observations can be explained as inverse Compton-dominated leptonic emission of relativistic electrons with a cutoff energy of 100−30+70 TeV. The low magnetic field in the source imposed by the X-ray upper limits on synchrotron emission is compatible with a hypothesis of a PWN or a TeV halo. Furthermore, the spectral properties of the HE counterpart are consistent with a Geminga-like pulsar, which would be able to power the VHE-UHE emission. Nevertheless, the lack of a pulsar in the neighborhood of the UHE source is a challenge to the PWN/TeV-halo scenario. The UHE γ rays can also be explained as π0 decay-dominated hadronic emission due to interaction of relativistic protons with one of the two known molecular clouds in the direction of the source. Indeed, the hard spectrum in the LST-1 band is compatible with protons escaping a shock around a middle-aged SNR because of their high low-energy cut-off, but the origin of the HE γ-ray emission remains an open question....
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ACS Earth and Space Chemistry 2023年3月9日 査読有り
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Journal of Geophysical Research: Space Physics 128(2) 2023年2月21日 査読有りWe present long-term density trends of the Earth's upper atmosphere at altitudes between 71 and 116 km, based on atmospheric occultations of the Crab Nebula observed with X-ray astronomy satellites, ASCA, RXTE, Suzaku, NuSTAR, and Hitomi. The combination of the five satellites provides a time period of 28 years from 1994 to 2022. To suppress seasonal and latitudinal variations, we concentrate on the data taken in autumn (49 < doy < 111) and spring (235 < doy < 297) in the northern hemisphere with latitudes of 0°-40°. With this constraint, local times are automatically limited either around noon or midnight. We obtain four sets (two seasons × two local times) of density trends at each altitude layer. We take into account variations due to a linear trend and the 11-year solar cycle using linear regression techniques. Because we do not see significant differences among the four trends, we combine them to provide a single vertical profile of trend slopes. We find a negative density trend of roughly -5%/decade at every altitude. This is in reasonable agreement with inferences from settling rate of the upper atmosphere. In the 100-110-km altitude, we found an exceptionally high density decline of about -12%/decade. This peak may be the first observational evidence for strong cooling due to water vapor and ozone near 110 km, which was first identified in a numerical simulation by Akmaev et al. (2006, <A href="https://doi.org/10.1016/j.jastp.2006.03.008">https://doi.org/10.1016/j.jastp.2006.03.008</A>). Further observations and numerical simulations with suitable input parameters are needed to establish this feature....
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Publications of the Astronomical Society of Japan 2022年10月 査読有りPulsar wind nebulae (PWNe) are one of the most energetic galactic sources with bright emissions from radio waves to very high-energy gamma-rays. We perform wideband X-ray spectroscopy of four energetic PWNe, N 157 B, PSR J1813-1749, PSR J1400-6325, and G21.5-0.9, with the Suzaku, Chandra, NuSTAR, and Hitomi observatories. A significant spectral break or cut-off feature is found in the hard X-ray band for all the samples, except for N 157 B. The break energies in the broken power-law fitting are in the range of 4-14 keV, whereas the cut-off energies in the cut-off power-law fitting are at 22 keV or higher. The break or cut-off energy does not show a significant correlation with either the spin-down energy or characteristic age of the hosting pulsars. A possible correlation is found between the photon index change in the broken power-law fitting and the X-ray emitting efficiency of the pulsars, although its significance is not high enough to be conclusive. We discuss what determines the break parameters based on simple models....
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 74(5) 1022-1040 2022年10月 査読有り
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Journal of Low Temperature Physics 209(5-6) 1088-1096 2022年9月19日 査読有りWe measured the vibration of a prototype superconducting magnetic bearing (SMB) operating at liquid nitrogen temperature. This prototype system was designed as a breadboard model for LiteBIRD low-frequency telescope (LFT) polarization modulator unit. We set an upper limit of the vibration amplitude at $36~\mathrm{\mu m}$ at the rotational synchronous frequency. During the rotation, the amplitude of the magnetic field produced varies. From this setup, we compute the static and AC amplitude of the magnetic fields produced by the SMB magnet at the location of the LFT focal plane as $0.24~\mathrm{G}$ and $3\times10^{-5}$$~\mathrm{G}$, respectively. From the AC amplitude, we compute TES critical temperature variation of $7\times10^{-8}$$~\mathrm{K}$ and fractional change of the SQUID flux is $\delta \Phi/\Phi_0|_{ac}=3.1\times10^{-5}$. The mechanical vibration can be also estimated to be $3.6\times 10^{-2}$$~\mathrm{N}$ at the rotation mechanism location....
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Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray 2022年8月31日
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Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray 2022年8月31日
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The Astrophysical Journal 2022年8月1日 査読有りSynchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high-energy electrons accelerated at the shock front and the acceleration process. We performed a spatially resolved spectral analysis of NuSTAR and XMM-Newton observations of the young Kepler's SNR, aiming to study in detail its nonthermal emission in hard X-rays. We selected a set of regions all around the rim of the shell and extracted the corresponding spectra. The spectra were analyzed by adopting a model of synchrotron radiation in the loss-limited regime, to constrain the dependence of the cutoff energy of the synchrotron radiation on the shock velocity. We identify two different regimes of particle acceleration, characterized by different Bohm factors. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with the dense CSM. Our results suggest an enhanced efficiency of the acceleration process in regions where the shock-CSM interaction generates an amplified and turbulent magnetic field. By combining hard X-ray spectra with radio and γ-ray observations of Kepler's SNR, we modeled the spectral energy distribution. In the light of our results we propose that the observed γ-ray emission is mainly hadronic and originates in the northern part of the shell....
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The Astrophysical Journal 933(1) 111-111 2022年7月1日 査読有り筆頭著者Abstract We perform a full nuclear-network numerical calculation of the r-process nuclei in binary neutron-star mergers (NSMs), with the aim of estimating gamma-ray emissions from the remnants of Galactic NSMs up to 106 yr old. The nucleosynthesis calculation of 4070 nuclei is adopted to provide the elemental composition ratios of nuclei with an electron fraction Ye between 0.10 and 0.45. The decay processes of 3237 unstable nuclei are simulated to extract the gamma-ray spectra. As a result, the NSMs have different spectral colors in the gamma-ray band from various other astronomical objects at less than 105 yr old. In addition, we propose a new line diagnostic method for Ye that uses the line ratios of either 137mBa/85K or 243Am/60mCo, which become larger than unity for young and old r-process sites, respectively, with a low-Ye environment. From an estimation of the distance limit for gamma-ray observations as a function of age, the high sensitivity in the sub-megaelectronvolt band, at approximately 10−9 photons s−1 cm−2 or 10−15 erg s−1 cm−2, is required to cover all the NSM remnants in our Galaxy, if we assume that the population of NSMs by Wu et al. A gamma-ray survey with sensitivities of 10−8–10−7 photons s−1 cm−2 or 10−14–10−13 erg s−1 cm−2 in the 70–4000 keV band is expected to find emissions from at least one NSM remnant under the assumption of an NSM rate of 30 Myr−1. The feasibility of gamma-ray missions observing Galactic NSMs is also studied.
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Publications of the Astronomical Society of Japan 2022年6月2日 査読有りUtilizing Chandra, XMM-Newton, and NuSTAR, a wide-band X-ray spectrum from 0.2 to 20 keV is reported from the western hotspot of Pictor A. In particular, the X-ray emission is significantly detected in the 3 to 20 keV band at 30σ by NuSTAR. This is the first detection of hard X-rays with energies above 10 keV from a jet termination hotspot of active galactic nuclei. The hard X-ray spectrum is well described with a power-law model with a photon index of Γ = 1.8 ± 0.2, and the flux is obtained to be (4.5 ± 0.4) × 10-13 erg s-1 cm-2 in the 3 to 20 keV band. The obtained spectrum is smoothly connected with those soft X-ray spectra observed by Chandra and XMM-Newton. The wide-band spectrum shows a single power-law spectrum with a photon index of Γ = 2.07 ± 0.03, excluding any cut-off/break features. Assuming the X-rays to be synchrotron radiation of the electrons, the energy index of the electrons is estimated as p = 2Γ - 1 = 3.14 ± 0.06 from the wide-band spectrum. Given that the X-ray synchrotron-emitting electrons quickly lose their initial energies via synchrotron radiation, the energy index of electrons at acceleration sites is estimated as pacc = p - 1 = 2.14 ± 0.06. This is consistent with the prediction of the diffusive shock acceleration. Since the spectrum has no cut-off feature up to 20 keV, the maximum electron energy is estimated to be no less than 40 TeV....
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VizieR Online Data Catalog 2022年6月During the period covered in the present catalog (2011-2021), the InterPlanetary Network (IPN) contained between seven and nine missions: the Konus-Wind (KW), in orbit around the Lagrangian point L1; Mars Odyssey (a gamma-ray spectrometer, GRS, that includes the High-Energy Neutron Detector, HEND, with GRB detection capabilities, Hurley+ 2006ApJS..164..124H), in orbit around Mars; the Mercury Surface, Space Environment, Geochemistry, and Ranging mission (MESSENGER); the Gamma-Ray and Neutron Spectrometer (GRNS; Gold+ 2001P&SS...49.1467G), in an eccentric orbit around Mercury; the International Gamma-Ray Laboratory (INTEGRAL; the anticoincidence shield of the spectrometer SPI (SPI-ACS), in an eccentric Earth orbit; Rau+ 2005, J/A+A/438/1175); RHESSI and the array of germanium detectors (GeD; Smith+ 2002SoPh..210...33S); the Neil Gehrels Swift Observatory (the Burst Alert Telescope, BAT); the Fermi Gamma-ray Space Telescope's Gamma-Ray Burst Monitor (GBM); the Suzaku mission (the Wide-band All-sky Monitor, WAM); the Astro-rivelatore Gamma a Immagini LEggero mission (AGILE); the Mini-Calorimeter (MCAL; Tavani+ 2009A&A...502..995T); the CALorimetric Electron Telescope on board the International Space Station (CALET); the Gamma-ray Burst Monitor; the Hard X-ray Modulation Telescope (Insight-HXMT; the High-energy X-ray Telescope, HE); and the Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM; gamma-ray detectors, GRDs; GECAM consists of two microsatellites, GECAM-A and GECAM-B, but currently only GECAM-B is in operation): all in low-Earth orbit. See Section 2. <P />(3 data files)....
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Publications of the Astronomical Society of Japan 74(2) 364-383 2022年4月4日 査読有りAbstract We have developed a simulation-based method of spectral analysis for pile-up-affected data of X-ray CCDs without any loss of photon statistics. As effects of the photon pile-up appear as complicated nonlinear detector responses, we employ a detailed simulation to calculate the important processes in an X-ray observation including physical interactions, detector signal generation, detector readout, and a series of data reduction processes. This simulation naturally reproduces X-ray-like and background-like events as results of X-ray photon merging in a single pixel or in a chunk of adjacent pixels, allowing us to construct a nonlinear spectral analysis framework that can treat pile-up-affected observation data. For validation, we have performed data analysis of Suzaku X-ray Imaging Spectrometer (XIS) observations using this framework with various parameters of the detector simulation, all of which are optimized for that instrument. We present three cases of different pile-up degrees: PKS 2155−304 (negligible pile-up), Aquila X-1 (moderate pile-up), and the Crab Nebula (strong pile-up); we show that the nonlinear analysis method produces results consistent with a conventional linear analysis for the negligible pile-up condition, and accurately corrects well-known pile-up effects such as spectral hardening and flux decrease for the pile-up cases. These corrected results are consistent with those obtained by a widely used core-exclusion method or by other observatories with much higher timing resolutions (without pile-up). Our framework is applicable to any types of CCDs used for X-ray astronomy, including future missions such as X-ray Imaging and Spectroscopy Mission (XRISM), by appropriate optimization of the simulation parameters.
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The Astrophysical Journal Supplement Series 2022年4月 査読有りWe present the catalog of InterPlanetary Network (IPN) localizations for 199 short-duration gamma-ray bursts (sGRBs) detected by the Konus-Wind (KW) experiment between 2011 January 1 and 2021 August 31, which extends the initial sample of IPN-localized KW sGRBs to 495 events. We present the most comprehensive IPN localization data on these events, including probability sky maps in Hierarchical Equal Area isoLatitude Pixelization format....
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The Astrophysical Journal 2021年12月 査読有りWe report on a discovery of an X-ray emitting circumstellar material knot inside the synchrotron dominant supernova remnant (SNR) RX J1713.7-3946. This knot was previously thought to be a Wolf-Rayet star (WR 85), but we realized that it is in fact $\sim$40$^{\prime\prime}$ away from WR 85, indicating no relation to WR 85. We performed high-resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The RGS spectrum clearly resolves a number of emission lines, such as N Ly$\alpha$, O Ly$\alpha$, Fe XVIII, Ne X, Mg XI, and Si XIII. The spectrum can be well represented by an absorbed thermal emission model with a temperature of $k_{\rm B}T_{\rm e} = 0.65\pm 0.02$ keV. The elemental abundances are obtained to be ${\rm N/H} = 3.5\pm 0.8{\rm \left(N/H\right)_{\odot } }$, ${\rm O/H} = 0.5\pm0.1{\rm \left(O/H\right)_{\odot } }$, ${\rm Ne/H} = 0.9\pm0.1{\rm \left(Ne/H\right)_{\odot } }$, ${\rm Mg/H} = 1.0\pm0.1{\rm \left(Mg/H\right)_{\odot } }$, ${\rm Si/H} = 1.0\pm0.2{\rm \left(Si/H\right)_{\odot } }$, and ${\rm Fe/H} = 1.3\pm0.1{\rm \left(Fe/H\right)_{\odot } }$. The enhanced N abundance with others being about the solar values allows us to infer that this knot is circumstellar material ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to O is obtained to be $\rm N/O = 6.8_{-2.1}^{+2.5}\left(N/O\right)_{\odot}$. By comparing this to those in outer layers of red supergiant stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be $15\, \rm M_{\odot} \lesssim \rm M \lesssim 20\, \rm M_{\odot}$....
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2021年11月In this report we summarize the activities of the International Astronomical Consortium for High Energy Calibration (IACHEC) and the work done since the last in-person meeting in Japan (Shonan Village Center), May 2019, through two virtual meetings that were held in November 2020 and May 2021. The on-line only meetings divided the contents of the usual in-person workshop between mission updates and working group updates. The November meeting was dedicated to mission calibration updates and the current status of the cross-calibration between NuSTAR, Swift, and NICER, which frequently join together in observations of bright transients, and a review of the XMM-Newton and Chandra cross-calibration. Results between \nustar\ and \swift\ overall show good agreement, but issues persist in the overlap region 3--5 keV for bright source with large dust scattering halos. The NICER cross-calibration is still progressing and evolving, while for the XMM-Newton and Chandra cross-calibration systematic differences both in the absolute flux and spectral shape determination still exists on different classes of sources. The meeting in May was focused on the Working Group progress and reports summarized here....
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Journal of Astronomical Telescopes, Instruments, and Systems 7(03) 2021年7月1日 査読有り筆頭著者
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Publications of the Astronomical Society of Japan 2021年4月5日 査読有り
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Journal of Geophysical Research: Space Physics 126(4) 2021年4月 査読有り
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Ground-based and Airborne Instrumentation for Astronomy VIII 114470H 2020年12月13日
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Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月13日
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Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月13日
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Astrophysics and Space Science 365(11) 2020年11月 査読有り
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Astronomy and Astrophysics 642 2020年10月 査読有り
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The Astrophysical Journal 891(2) 126-126 2020年3月12日 査読有り
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The Astrophysical Journal 2020年2月 査読有りWe have performed a systematic study of gamma-ray bursts (GRBs), which have various values in the peak energy of the νFν spectrum of prompt emission, Epeak, observed by the Swift/Burst Alert Telescope (BAT) and Fermi/Gamma-ray Burst Monitor, investigating their prompt and X-ray afterglow emissions. We cataloged long-lasting GRBs observed by Swift between 2004 December and 2014 February in three categories according to the classification by Sakamoto et al.: X-ray flashes (XRFs), X-ray-rich GRBs (XRRs), and classical GRBs (C-GRBs). We then derived ${E}_{\mathrm{peak } }^{\mathrm{obs } }$ , as well as ${E}_{\mathrm{peak } }^{\mathrm{src } }$ if viable, of the Swift spectra of their prompt emission. We also analyzed their X-ray afterglows and found that GRB events with a lower ${E}_{\mathrm{peak } }^{\mathrm{src } }$ , I.e., softer GRBs, are fainter in 0.3-10 keV X-ray luminosity and decay more slowly than harder GRBs. The intrinsic event rates of the XRFs, XRRs, and C-GRBs were calculated using the Swift/BAT trigger algorithm. Those of the XRRs and XRFs are larger than that of the C-GRBs. If we assume that the observational diversity of Epeak is explained using the off-axis model, these results yield a jet half-opening angle of Δθ ∼ 0°3, and a variance of the observing angles θobs ≲ 0°6. This implies that this tiny variance would be responsible for the Epeak diversity observed by Swift/BAT, which is unrealistic. Therefore, we conclude that the Epeak diversity is not explained with the off-axis model, but is likely to originate from some intrinsic properties of the jets....
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Proceedings of SPIE - The International Society for Optical Engineering 11443 2020年
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Journal of Astronomical Telescopes, Instruments, and Systems 6(4) 2020年 査読有り
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2020年1月We summarize the 14th meeting of the International Astronomical Consortium for High Energy Calibration (IACHEC) held at \textit{Shonan Village} (Kanagawa, Japan) in May 2019. Sixty scientists directly involved in the calibration of operational and future high-energy missions gathered during 3.5 days to discuss the status of the cross-calibration between the current international complement of X-ray observatories, and the possibilities to improve it. This summary consists of reports from the various WGs with topics ranging from the identification and characterization of standard calibration sources, multi-observatory cross-calibration campaigns, appropriate and new statistical techniques, calibration of instruments and characterization of background, communication and preservation of knowledge, and results for the benefit of the astronomical community....
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Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年
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Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年
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Publications of the Astronomical Society of Japan 71(4) 2019年8月 査読有り
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The Astrophysical Journal 878(2) 121-121 2019年6月20日 査読有り
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2019年3月The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document....
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2019年1月We summarize the outcome of the 13th meeting of the International Astronomical Consortium for High Energy Calibration (IACHEC), held at Tenuta dei Ciclamini (Avigliano Umbro, Italy) in April 2018. Fifty-one scientists directly involved in the calibration of operational and future high-energy missions gathered during 3.5 days to discuss the current status of the X-ray payload inter-calibration and possible approaches to improve it. This summary consists of reports from the various working groups with topics ranging from the identification and characterization of standard calibration sources, multi-observatory cross-calibration campaigns, appropriate and new statistical techniques, calibration of instruments and characterization of background, and communication and preservation of knowledge and results for the benefit of the astronomical community....
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 70(6) 2018年12月 査読有り
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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 894 1-7 2018年6月21日 査読有り
MISC
278-
2024年2月12日欧州第一回XRISM科学データ解析ワークショップ 開催主催
書籍等出版物
4-
World Scientific Publishing Co. Pte. Ltd., 2019年1月 (ISBN: 9789813270091)
講演・口頭発表等
159-
XRISM International Conference 2025 - sponsored by the JSPS core-to-core program - 2025年10月20日
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The Golden Age of Cataclysmic Variables and Related Objects - VII 2025年9月2日 招待有り
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the 17th International Astrophysical Consortium for High Energy Calibration Workshop 2025年5月16日
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the 17th International Astrophysical Consortium for High Energy Calibration Workshop 2025年5月13日
所属学協会
6-
2011年2月
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2002年10月
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1998年9月
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1998年9月
共同研究・競争的資金等の研究課題
12-
日本学術振興会 2022年4月 - 2027年3月
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日本学術振興会 科学研究費助成事業 2021年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2021年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2020年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2018年4月 - 2020年3月
