研究者業績
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 特任准教授
- 学位
- 博士(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
10経歴
7-
2007年10月 - 現在
-
2003年10月 - 2007年9月
-
2003年10月 - 2007年9月
-
2003年3月 - 2003年9月
-
2003年3月 - 2003年9月
学歴
4委員歴
2-
2017年6月 - 2019年6月
-
2013年4月 - 2019年4月
論文
295-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 52-52 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 236-236 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 224-224 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 235-235 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 61-61 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 60-60 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 92-92 2024年8月21日
-
The Astrophysical Journal Letters 2024年1月1日
-
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1050 168175-168175 2023年5月
-
Journal of Geophysical Research: Space Physics 128(2) 2023年2月21日
-
Scientific Reports 12(1) 2022年12月Abstract Elemental analysis based on muonic X-rays resulting from muon irradiation provides information about bulk material composition without causing damage, which is essential in the case of precious or otherwise unreachable samples, such as in archeology and planetary science. We developed a three-dimensional (3D) elemental analysis technique by combining the elemental analysis method based on negative muons with an imaging cadmium telluride double-sided strip detector (CdTe-DSD) designed for the hard X-ray and soft $$\gamma$$-ray observation. A muon irradiation experiment using spherical plastic samples was conducted at the Japan Proton Accelerator Research Complex (J-PARC); a set of projection images was taken by the CdTe-DSD, equipped with a pinhole collimator, for different sample rotation angles. The projection images measured by the CdTe-DSD were utilized to obtain a 3D volumetric phantom by using the maximum likelihood expectation maximization algorithm. The reconstructed phantom successfully revealed the 3D distribution of carbon in the bulk samples and the stopping depth of the muons. This result demonstrated the feasibility of the proposed non-destructive 3D elemental analysis method for bulk material analysis based on muonic X-rays.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 74(5) 1022-1040 2022年10月A novel collisionless shock jump condition is suggested by modeling the entropy production at the shock transition region. We also calculate downstream developments of the atomic ionization balance and the ion temperature relaxation in supernova remnants (SNRs). The injection process and subsequent acceleration of cosmic rays (CRs) in the SNR shocks are closely related to the formation process of the collisionless shocks. The formation of the shock is caused by wave-particle interactions. Since the wave-particle interactions result in energy exchanges between electromagnetic fields and charged particles, the randomization of particles associated with the shock transition may occur at a rate given by the scalar product of the electric field and current. We find that order-of-magnitude estimates of the randomization with reasonable strength of the electromagnetic fields in the SNR constrain the amount of CR nuclei and the ion temperatures. The constrained amount of CR nuclei can be sufficient to explain the Galactic CRs. The ion temperature becomes significantly lower than that in the case without CRs. To distinguish the case without CRs, we perform synthetic observations of atomic line emissions from the downstream region of the SNR RCW 86. Future observations by XRISM and Athena can distinguish whether the SNR shock accelerates the CRs or not from the ion temperatures.
-
ASTRONOMY & ASTROPHYSICS 665 2022年9月 査読有りContext. Solar nanoflares are small impulsive events releasing magnetic energy in the corona. If nanoflares follow the same physics as their larger counterparts, they should emit hard X-rays (HXRs) but with a rather faint intensity. A copious and continuous presence of nanoflares would result in a sustained HXR emission. These nanoflares could deliver enormous amounts of energy into the solar corona, possibly accounting for its high temperatures. To date, there has not been any direct observation of such persistent HXRs from the quiescent Sun. However, the quiet-Sun HXR emission was constrained in 2010 using almost 12 days of quiescent solar off-pointing observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). These observations set 2 sigma upper limits at 3.4 x 10(-2) photons s(-1) cm(-2) keV(-1) and 9.5 x 10(-4) photons s(-1) cm(-2) keV(-1) for the 3-6 keV and 6-12 keV energy ranges, respectively. Aims. Observing faint HXR emission is challenging because it demands high sensitivity and dynamic range instruments. The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment excels in these two attributes when compared with RHESSI. FOXSI completed its second and third successful flights (FOXSI-2 and -3) on December 11, 2014, and September 7, 2018, respectively. This paper aims to constrain the quiet-Sun emission in the 5-10 keV energy range using FOXSI-2 and -3 observations. Methods. To fully characterize the sensitivity of FOXSI, we assessed ghost ray backgrounds generated by sources outside of the field of view via a ray-tracing algorithm. We used a Bayesian approach to provide upper thresholds of quiet-Sun HXR emission and probability distributions for the expected flux when a quiet-Sun HXR source is assumed to exist. Results. We found a FOXSI-2 upper limit of 4.5 x 10(-2) photons s(-1) cm(-2) keV(-1) with a 2 sigma confidence level in the 5-10 keV energy range. This limit is the first-ever quiet-Sun upper threshold in HXR reported using similar to 1 min observations during a period of high solar activity. RHESSI was unable to measure the quiet-Sun emission during active times due to its limited dynamic range. During the FOXSI-3 flight, the Sun exhibited a fairly quiet configuration, displaying only one aged nonflaring active region. Using the entire similar to 6.5 min of FOXSI-3 data, we report a 2 sigma upper limit of similar to 10(-4) photons s(-1) cm(-2) keV(-1) for the 5-10 keV energy range. Conclusions. The FOXSI-3 upper limits on quiet-Sun emission are similar to that previously reported, but FOXSI-3 achieved these results with only 5 min of observations or about 1/2600 less time than RHESSI. A possible future spacecraft using hard X-ray focusing optics like those in the FOXSI concept would allow enough observation time to constrain the current HXR quiet-Sun limits further, or perhaps even make direct detections. This is the first report of quiet-Sun HXR limits from FOXSI and the first science paper using FOXSI-3 observations.
-
Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray 2022年8月31日
-
Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray 2022年8月31日
-
RADIOISOTOPES 71(2) 141-151 2022年7月15日
-
Astrophysical Journal 933(2) 2022年7月1日We conduct a wide-band X-ray spectral analysis in the energy range of 1.5-100 keV to study the time evolution of the M7.6-class flare of 2016 July 23, with the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft. With the combination of MinXSS for soft X-rays and RHESSI for hard X-rays, a nonthermal component and three-temperature multithermal component - "cool"(T ≈ 3 MK), "hot"(T ≈ 15 MK), and "superhot"(T ≈ 30 MK) - were measured simultaneously. In addition, we successfully obtained the spectral evolution of the multithermal and nonthermal components with a 10 s cadence, which corresponds to the Alfvén timescale in the solar corona. We find that the emission measures of the cool and hot thermal components are drastically increasing more than hundreds of times and the superhot thermal component is gradually appearing after the peak of the nonthermal emission. We also study the microwave spectra obtained by the Nobeyama Radio Polarimeters, and we find that there is continuous gyrosynchrotron emission from mildly relativistic nonthermal electrons. In addition, we conducted a differential emission measure (DEM) analysis by using Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and determined that the DEM of cool plasma increases within the flaring loop. We find that the cool and hot plasma components are associated with chromospheric evaporation. The superhot plasma component could be explained by the thermalization of the nonthermal electrons trapped in the flaring loop.
-
The Astrophysical Journal 933(1) 111-111 2022年7月1日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.
-
Publications of the Astronomical Society of Japan 2022年5月 査読有り
-
Publications of the Astronomical Society of Japan 74(2) 364-383 2022年4月4日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.
-
2021年10月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 $15\, \rm M_{\odot} \lesssim \rm M \lesssim 20\, \rm M_{\odot}$....
-
Astrophysical Journal 917(2) 2021年8月20日We report a detailed analysis of the hard X-ray and GeV gamma-ray spectra of LS 5039, one of the brightest gamma-ray binary system in the Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) observation covering its entire orbit in 2016 allowed us for the first time to study the orbital variability of the spectrum above 10 keV. The hard X-ray spectrum is well described with a single power-law component up to 78 keV. The X-ray flux showed a slight deviation from those observed previously with Suzaku in 2007. The fast X-ray brightening observed with Suzaku, around the inferior conjunction, was not observed in this observation. We also analyzed 11 yr of Fermi Large Area Telescope data of LS 5039. The GeV spectrum around the inferior conjunction was well described with two nonthermal components: a power law with a photon index of ∼3 and a cutoff power law with a cutoff energy of ∼2 GeV. The orbital flux variability also changed gradually around a few GeV. These results indicate that there are two emission components in the GeV band, and the dominant component above ∼1 GeV does not depend on the orbital phase. By combining these results, we update the spectral energy distribution of LS 5039 with the highest available statistics. Theoretical models proposed so far cannot explain the obtained multiwavelength spectrum, especially the emission from ∼1 to ∼400 MeV, and we discuss the possibility that particle acceleration in LS 5039 is different from the shock acceleration.
-
Journal of Astronomical Telescopes, Instruments, and Systems 7(03) 2021年7月1日
-
Review of Scientific Instruments 92(6) 2021年6月1日 査読有りMethods to measure the polarization of x rays from highly charged heavy ions with a significantly higher accuracy than that of the existing technology are needed to explore relativistic and quantum electrodynamics effects, including the Breit interaction. We developed an Electron Beam Ion Trap Compton Camera (EBIT-CC), a new Compton polarimeter with pixelated multi-layer silicon, and cadmium telluride counters. The EBIT-CC detects the three-dimensional position of Compton scattering and photoelectric absorption, and thus, the degree of polarization of incoming x rays can be evaluated. We attached the EBIT-CC on the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) in the University of Electro-Communications. An experiment was performed to evaluate its polarimetric capability through an observation of radiative recombination x rays emitted from highly charged krypton ions, which were generated by the Tokyo-EBIT. The CC of the EBIT-CC was calibrated for the ∼75 keV x rays. We developed event reconstruction and selection procedures and applied them to every registered event. As a result, we successfully obtained the polarization degree with an absolute uncertainty of 0.02. This uncertainty is small enough to probe the difference between the zero-frequency approximation and full-frequency-dependent calculation for the Breit interaction, which is expected for dielectronic recombination x rays of highly charged heavy ions.
-
Publications of the Astronomical Society of Japan 2021年4月5日
-
Journal of Geophysical Research: Space Physics 126(4) 2021年4月
-
Ground-based and Airborne Instrumentation for Astronomy VIII 114470H 2020年12月13日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月13日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月13日
-
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 982 2020年12月1日 査読有りWe present our latest ASIC, which is used for the readout of Cadmium Telluride double-sided strip detectors (CdTe DSDs) and high spectroscopic imaging. It is implemented in a 0.35 μm CMOS technology (X-Fab XH035), consists of 64 readout channels and has a function that performs simultaneous AD conversion for each channel. The equivalent noise charge of 54.9e− ± 11.3e− (rms) is measured without connecting the ASIC to any detectors. From the spectroscopy measurements using a CdTe single-sided strip detector, the energy resolution of 1.12 keV (FWHM) is obtained at 13.9 keV, and photons within the energy from 6.4 keV to 122.1 keV are detected. Based on the experimental results, we propose a new low-noise readout architecture making use of a slew-rate limited mode at the shaper followed by a peak detector circuit.
-
Astrophysics and Space Science 365(11) 2020年11月
-
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 978 2020年10月21日 査読有りWe have evaluated the performance of a fine pitch CdTe Double-sided Strip Detector (CdTe-DSD), which was originally developed for the focal plane detector of a hard X-ray telescope to observe the Sun. The detector has a thickness of 750 μm and has 128 strip electrodes with a 60 μm strip pitch orthogonally placed on both sides of the detector and covers an energy range 4 keV to 80 keV. The study of the depth of photon interaction and charge sharing effects are of importance in order to provide good spectroscopic and imaging performance. We study the tail structure observed in the spectra caused by charge trapping and develop a new method to reconstruct the spectra based on induced charge information from both anode and cathode strips. By applying this method, energy resolutions (FWHM) of 0.76 keV and 1.0 keV can be obtained at photon energies of 14 keV and 60 keV, respectively, if the energy difference between the anode and cathode is within 1 keV. Furthermore, the tail component at 60 keV is reduced, and the energy resolution of the 60 keV peak is improved from 2.4 keV to 1.5 keV (FWHM) if the energy difference is greater than 1 keV. In order to study the imaging performance, we constructed a simple imaging system using a 5 mm thick tungsten plate that has a pinhole with a diameter of 100 μm. We utilize a 133Ba radioisotope of 1 mm in diameter as a target source in combination with a 100 μm slit made from 0.5 mm thickness tungsten. We imaged the 133Ba source behind the 100 μm slit using a 30 keV peak, with a 100 μm pinhole placed at the center of the source-detector distance. By applying a charge sharing correction between strips, we have succeeded in obtaining a position resolution better than the strip pitch of 60 μm.
-
Astronomy and Astrophysics 642 2020年10月We present the confirmation and characterisation of GJ 3473 b (G 50-16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal (P = 1.1980035 ± 0.0000018 d) was first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass, Mb = 1.86 ± 0.30 M⊕, and radius, Rb = 1.264 ± 0.050 R⊕. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass, Mc sin i = 7.41 ± 0.91 M⊕, and orbital period, Pc = 15.509 ± 0.033 d. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy. <P />RV data are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A236">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A236</A>...
-
The Astrophysical Journal 891(2) 126-126 2020年3月12日
-
Physics in Medicine & Biology 65(5) 05LT01 2020年3月1日The Compton camera can simultaneously acquire images of multiple isotopes injected in a body; therefore, it has the potential to introduce a new subfield in the field of biomedical imaging applications. The objective of this study is to assess the ability of a prototype semiconductor-based silicon/cadmium telluride (Si/CdTe) Compton camera to simultaneously image the distributions of technetium (99mTc)-dimercaptosuccinic acid (DMSA) (141 keV emission) and 18F-fluorodeoxyglucose (FDG) (511 keV emission) injected into a human volunteer. 99mTc-DMSA and 18F-FDG were injected intravenously into a 25-year-old male volunteer. The distributions of 99mTc-DMSA and 18F-FDG were simultaneously made visible by setting a specified energy window for each radioisotope. The images of these radiopharmaceuticals acquired using the prototype Compton camera were superimposed onto computed tomography images for reference. The reconstructed image showed that 99mTc-DMSA had accumulated in both kidneys, which is consistent with the well-known diagnostic distribution determined by clinical imaging via single-photon emission computed tomography. In the 18F-FDG image, there is broad distribution around the liver and kidneys, which was expected based on routine clinical positron emission tomography imaging. The current study demonstrated for the first time that the Si/CdTe Compton camera was capable of simultaneously imaging the distributions of two radiopharmaceuticals, 99mTc-DMSA and 18F-FDG, in a human body. These results suggest that the Si/CdTe Compton camera has the potential to become a novel modality for nuclear medical diagnoses enabling multi-probe simultaneous tracking.
-
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 954 2020年2月21日Compton imaging is a promising gamma-ray imaging method based on the Compton scattering kinematics due to high Compton scattering probability for sub-MeV to MeV gamma-rays. A conventional Compton camera has a disadvantage of low signal-to-background ratio (SBR), which is caused by drawing of multiple Compton cones. A method to solve this fundamental problem is the double-photon emission computed tomography (DPECT), which uses the coincidence detection for cascade gamma-rays and significantly increases the SBR using intersections of two Compton cones. In this study, we demonstrated the DPECT method by using 134Cs radio isotope, which is one of important radioisotopes for the imaging of fuel debris, with two Ce:Gd3(Al,Ga)5O12 (GAGG) scintillator Compton cameras.
-
The Astrophysical Journal 2020年2月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....
-
Journal of Astronomical Telescopes, Instruments, and Systems 6(4) 2020年Understanding and reducing in-orbit instrumental backgrounds are essential to achieving high sensitivity in hard x-ray astronomical observations. The observational data of the Hard X-ray Imager (HXI) onboard the Hitomi satellite provide useful information on the background components due to its multilayer configuration with different atomic numbers: the HXI consists of a stack of four layers of Si (Z = 14) detectors and one layer of cadmium telluride (CdTe) (Z = 48, 52) detector surrounded by well-type Bi4Ge3O12 active shields. Based on the observational data, the backgrounds of the top Si layer, the three underlying Si layers, and the CdTe layer are inferred to be dominated by different components, namely, low-energy electrons, albedo neutrons, and proton-induced radioactivation, respectively. Monte Carlo simulations of the in-orbit background of the HXI reproduce the observed background spectrum of each layer well, thereby quantitatively verifying the above hypothesis. In addition, we suggest the inclusion of an electron shield to reduce the background....
-
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....
-
Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年© 2020 SPIE The X-Ray Imaging and Spectroscopy Mission, XRISM, is currently scheduled to launch in 2022 with the objective of building on the brief, but significant, successes of the ASTRO-H (Hitomi) mission in solving outstanding astrophysical questions using high resolution X-ray spectroscopy. The XRISM Science Operations Team (SOT) consists of the JAXA-led Science Operations Center (SOC) and NASA-led Science Data Center (SDC), which work together to optimize the scientific output from the Resolve high-resolution spectrometer and the Xtend wide-field imager through planning and scheduling of observations, processing and distribution of data, development and distribution of software tools and the calibration database (CaldB), support of ground and in-flight calibration, and support of XRISM users in their scientific investigations of the energetic universe. Here, we summarize the roles and responsibilities of the SDC and its current status and future plans. The Resolve instrument poses particular challenges due to its unprecedented combination of high spectral resolution and throughput, broad spectral coverage, and relatively small field-of-view and large pixel-size. We highlight those challenges and how they are being met.
-
Proceedings of SPIE - The International Society for Optical Engineering 11444 2020年© 2020 SPIE The XRISM is the X-ray astronomical mission led by JAXA/NASA/ESA with international participation, plan to be launched in 2022 (Japanese fiscal year), to quickly recover the high-resolution X-ray spectroscopy of astrophysical objects using the micro-calorimeter array after the failure of Hitomi. To enhance the scientific outputs of the mission, the Science Operations Team (SOT) is structured independently from the instrument teams and the mission operation team (MOT). The responsibilities of the SOT are summarized into four categories: 1) Guest observer program and data distributions, 2) Distribution of the analyses software and calibration database, 3) Guest observer supporting activities, and 4) the performance verification and optimization (PVO) activities. Before constructing the Operations Concept of the XRISM mission, the lessons on the Science Operations learned from the past Japanese X-ray missions (ASCA, Suzaku, and Hitomi) are reviewed, and 16 kinds of lessons are identified by the above categories: lessons on the importance of avoiding nonpublic (“animal”) tools, coding quality of public tools both on the engineering viewpoint and the calibration accuracy, tight communications with instrument teams and operations team, well-defined task division between scientists and engineers etc. Among these lessons, a) importance of the early preparations of the operations from the ground stage, b) construction of the independent team for the Science Operations from the instrument developments, and c) operations with well-defined duties by appointed members are recognized as the key lessons for XRISM. Then, i) the task division between the Mission and Science Operations and ii) the subgroup structure within the XRISM team are defined in detail as the XRISM Operations Concept. Then, following the Operations Concept, the detail plan of the Science Operations is designed as follows. The Science Operations tasks are shared among Japan, US, and Europe operated by three centers, the Science Operations Center (SOC) at JAXA, the Science Data Center (SDC) at NASA, and European Space Astronomy Centre (ESAC) at ESA. The SOT is defined as a combination of the SOC and SDC; the SOC is designed to perform tasks close to the spacecraft operations, such as spacecraft planning of science targets, quick-look health checks, pre-pipeline data processing, etc., and the SDC covers the tasks on the data calibration processing (pipeline processing), maintenance of the analysis tools etc. The data-archive and users-support activities are planned to be covered both by the SOC and SDC. Finally, the details of the Science Operations tasks and the tools for the Science Operations are also described in this paper. This information would be helpful for a construction of Science Operations of future X-ray missions.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 71(4) 2019年8月 査読有り
-
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 924 321-326 2019年4月 査読有り© 2018 Elsevier B.V. FOXSI-3 (Focusing Optics X-ray Solar Imager) is an international sounding rocket experiment to observe hard X-rays from the Sun. The previous two flights successfully demonstrated the efficacy of the concept of direct solar imaging in hard X-ray band. For the third launch scheduled in the summer of 2018, we have fabricated a prototype of the CdTe Double-sided Strip Detector. To evaluate the basic performance, laboratory tests were conducted. Energy resolution (FWHM) of 0.8 keV at 13.9 keV and 1.3 keV at 59.5 keV are confirmed. Since the optic angular resolution is finer than the strip pitch of the detector at the focal plane, sub-strip position determination is important to make full use of the high precision of the optic. To test the possibility of sub-strip resolution, we developed a new method of investigating the detector strips with a fine multi-pinhole collimator. The results of the analysis were highly favorable and we confirmed the sub-strip resolution by making sub-strip images of multi-pinholes and flat-irradiation. The spectral uniformity over the detector is also confirmed using the sub-strip image of flat-irradiation.
-
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 924 327-331 2019年4月 査読有り© 2018 Elsevier B.V. The soft gamma-ray detector (SGD) onboard Hitomi, which has a unique design concept, based on the combination of a ”narrow-field multi-layer semi-conductor Compton camera” and an active shielding, realizes astronomical observations in the 60−600 keV energy band with a high sensitivity. Development of optimum event selection criteria is essential for deriving the best observational performance of the SGD, but it is challenging because many parameters such as the detected photon energy, the Compton-scattering angle, and distance of each hit, among others, are non-linearly correlated. In this study, we propose a new method for distinguishing the signal from the background in the multi-parameter space utilizing a machine-learning approach. Our preliminary result, which uses both on-ground experimental data with good photon statistics and flight data with real in-orbit background and signal information, suggests that this approach might a good guide for an optimal event selection by the Compton camera.
-
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....
-
The Astrophysical Journal 2019年We present an analysis of the spectral shape and pulse profile of the accretion-powered pulsar 4U 1626-67 observed with Suzaku and Nuclear Spectroscopic Telescope Array (NuSTAR) during a spin-up state. The pulsar, which experienced a torque reversal to spin-up in 2008, has a spin period of ∼7.7 s. Comparing the phase-averaged spectra obtained with Suzaku in 2010 and with NuSTAR in 2015, we find that the spectral shape changed between the two observations: the 3-10 keV flux increased by ∼5%, while the 30-60 keV flux decreased significantly by ∼35%. Phase-averaged and phase-resolved spectral analysis shows that the continuum spectrum observed by NuSTAR is well described by an empirical negative and positive power law times exponential continuum with an added broad Gaussian emission component around the spectral peak at ∼20 keV. Taken together with the observed \dot{P} value obtained from the Fermi/gamma-ray burst monitor data, we conclude that the spectral change between the Suzaku and NuSTAR observations was likely caused by an increase in the accretion rate. We also report the possible detection of asymmetry in the profile of the fundamental cyclotron line. Furthermore, we present a study of the energy-resolved pulse profiles using a new relativistic ray tracing code, where we perform a simultaneous fit to the pulse profiles assuming a two-column geometry with a mixed pencil- and fan-beam emission pattern. The resulting pulse profile decompositions enable us to obtain geometrical parameters of accretion columns (inclination, azimuthal and polar angles) and a fiducial set of beam patterns. This information is important to validate the theoretical predictions from radiation transfer in a strong magnetic field....
-
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....
-
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 912 191-194 2018年12月
MISC
243講演・口頭発表等
36共同研究・競争的資金等の研究課題
12-
日本学術振興会 科学研究費助成事業 2021年4月 - 2026年3月
-
日本学術振興会 科学研究費助成事業 2020年4月 - 2025年3月
-
日本学術振興会 科学研究費助成事業 2018年4月 - 2020年3月
-
日本学術振興会 科学研究費助成事業 2015年4月 - 2017年3月
-
日本学術振興会 科学研究費助成事業 2011年4月 - 2016年3月
