DOI： 10.22541/essoar.172494465.55461132/v1

掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

Heating of charged particles via collisionless shocks, while ubiquitous in the universe, is an intriguing yet puzzling plasma phenomenon. One outstanding question is how electrons and ions approach an equilibrium after they were heated to different immediate-postshock temperatures. In order to fill the significant lack of observational information of the downstream temperature-relaxation process, we observe a thermal-dominant X-ray filament in the northwest of SN 1006 with Chandra. We divide this region into four layers with a thickness of 15́́ or 0.16 pc each, and fit each spectrum by a non-equilibrium ionization collisional plasma model. The electron temperature was found to increase toward downstream from 0.52–0.62 to 0.82–0.95 keV on a length scale of 60́́ (or 0.64 pc). This electron temperature is lower than thermal relaxation processes via Coulomb scattering, requiring some other effects such as plasma mixture due to turbulence and/or projection effects, etc., which we hope will be resolved with future X-ray calorimeter missions such as XRISM and Athena.

DOI： 10.1093/pasj/psae049

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Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

Non-Thermal components in the intra-cluster medium (ICM), such as turbulence, magnetic field, and cosmic rays, imprint the past and current energetic activities of jets from active galactic nuclei (AGN) of member galaxies as well as disturbance caused by galaxy cluster mergers. Meter-and centimeter-radio observations of synchrotron radiation allow us to diagnose the nonthermal component. Here we report on our discovery of an unidentified diffuse radio source, named the Flying Fox, near the center of the Abell 1060 field. The Flying Fox has an elongated ring-like structure and a central bar shape, but there is no obvious host galaxy. The average spectral index of the Flying Fox is-1.4, which is steeper than that for radio sources seen at meter wavelengths. We discussed the possibilities of radio lobes, phoenixes, radio halos and relics, and an odd radio circle. In conclusion, the Flying Fox is not clearly explained by known radio sources.

DOI： 10.1093/pasj/psae011

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

We developed the X-ray, gamma-ray, and relativistic electron detector (XGRE) onboard the Tool for the Analysis of RAdiation from lightNIngs and Sprites (TARANIS) satellite, to investigate high-energy phenomena associated with lightning discharges such as terrestrial gamma-ray flashes and terrestrial electron beams. XGRE consisted of three sensors. Each sensor has one layer of LaBr3 crystals for X-ray/gamma-ray detections and two layers of plastic scintillators for electron and charged-particle discrimination. Since 2018, the flight model of XGRE was developed, and validation and calibration tests, such as a thermal cycle test and a calibration test with the sensors onboard the satellite, were performed before the launch of TARANIS on 17 November 2020. The energy range of the LaBr3 crystals sensitive to X-rays and gamma rays was determined to be 0.04 to 11.6 MeV, 0.08 to 11.0 MeV, and 0.08 to 11.3 MeV for XGRE1, 2, and 3, respectively. The energy resolution at 0.662 MeV (full width at half maximum) was 20.5%, 25.9%, and 28.6%, respectively. The results from the calibration test were then used to validate a simulation model of XGRE and TARANIS. By performing Monte Carlo simulations with the verified model, we calculated effective areas of XGRE to X-rays, gamma rays, electrons, and detector responses to incident photons and electrons coming from various elevation and azimuth angles.

DOI： 10.1117/1.JATIS.10.2.026005

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Scopus

記述言語：日本語   出版者・発行元：宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)  

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Research Letters  

Relativistic Runaway Electrons Avalanches (RREAs) development depends on the applied electric field and the environment's air density. This dependency controls the RREA exponential growth length scale. The RREA development affects the bremsstrahlung excess occurring due to the passage of charged particles through the thundercloud's electric fields, the gamma-ray glow. We used Monte Carlo simulations to develop an empirical model showing the RREA behavior in a realistic atmospheric density profile. The new formulation shows how the density variation modulates the electron population under electric field strengths near the RREA electric field threshold. The model limits the initial RREA altitude range as a function of the electric field strength. The new model is valid between ∼0.6 and ∼18 km, covering the relevant heights to investigate the generation of ground-detected gamma-ray glows.

DOI： 10.1029/2023GL105087

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記述言語：日本語   出版者・発行元：宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)  

レポート番号: isas23-sbs-032

CiNii Research

記述言語：日本語   出版者・発行元：宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)  

レポート番号: isas23-sbs-014

CiNii Research

記述言語：日本語   出版者・発行元：宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)  

レポート番号: isas23-sbs-033

CiNii Research

出版者・発行元：Astronomy and Astrophysics  

Aims. Since it launched on 22 March 2021, the 1U-sized CubeSat GRBAlpha operates and collects scientific data on high-energy transients, making it the smallest astrophysical space observatory to date. GRBAlpha is an in-orbit demonstration of a gamma-ray burst (GRB) detector concept suitably small to fit into a standard 1U volume. As was demonstrated in a companion paper, GRBAlpha adds significant value to the scientific community with accurate characterization of bright GRBs, including the recent outstanding event of GRB 221009A. Methods. The GRB detector is a 75 × 75 × 5 mm CsI(Tl) scintillator wrapped in a reflective foil (ESR) read out by an array of SiPM detectors, multi-pixel photon counters by Hamamatsu, driven by two separate redundant units. To further protect the scintillator block from sunlight and protect the SiPM detectors from particle radiation, we applied a multi-layer structure of Tedlar wrapping, anodized aluminium casing, and a lead-alloy shielding on one edge of the assembly. The setup allows observations of gamma radiation within the energy range of 70- 890 keV with an energy resolution of ~30%. Results. Here, we summarize the system design of the GRBAlpha mission, including the electronics and software components of the detector, some aspects of the platform, and the current semi-autonomous operations. In addition, details are given about the raw data products and telemetry in order to encourage the community to expand the receiver network for our initiatives with GRBAlpha and related experiments.

DOI： 10.1051/0004-6361/202346182

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出版者・発行元：Astronomy and Astrophysics  

Context. On 2022 October 9 the brightest gamma-ray burst (GRB) ever observed lit up the high-energy sky. It was detected by a multitude of instruments, attracting the close attention of the GRB community, and saturated many detectors. Aims. GRBAlpha, a nano-satellite with a form factor of a 1U CubeSat, detected this extraordinarily bright long-duration GRB, GRB 221009A, without saturation but affected by pile-up. We present light curves of the prompt emission in 13 energy bands, from 80 keV to 950 keV, and performed a spectral analysis to calculate the peak flux and peak isotropic-equivalent luminosity. Methods. Since the satellite s attitude information is not available for the time of this GRB, more than 200 incident directions were probed in order to find the median luminosity and its systematic uncertainty. Results. We find that the peak flux in the 80-800 keV range (observer frame) was Fph p = 1300+ -1200 200 ph cm-2 s-1, or Ferg p = 5:7+ -3 0::7 7×10-4 erg cm-2 s-1, and the fluence in the same energy range of the first GRB episode, which lasted 300 s and was observable by GRBAlpha, was S = 2:2+1:4 -0:3 × 10-2 erg cm-2, or S bol = 4:9+0:8 -0:5 × 10-2 erg cm-2 for the extrapolated range of 0:9-8690 keV. We infer the isotropic-equivalent released energy of the first GRB episode to be Eiso bol = 2:8+ -0 0::8 5 × 1054 erg in the 1-10 000 keV band (rest frame at z = 0:15). The peak isotropic-equivalent luminosity in the 92-920 keV range (rest frame) was Liso p = 3:7+ -2 0::5 5 × 1052 erg s-1, and the bolometric peak isotropic-equivalent luminosity was Lp;bol iso = 8:4+-21::55 × 1052 erg s-1 (4 s scale) in the 1-10 000 keV range (rest frame). The peak emitted energy is Ep*= Ep(1 + z) = 1120 ± 470 keV. Our measurement of Lp;bol iso is consistent with the Yonetoku relation. It is possible that, due to the spectral evolution of this GRB and the orientation of GRBAlpha at the peak time, the true values of peak flux, fluence, Liso, and Eiso are even higher.

DOI： 10.1051/0004-6361/202346128

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Sissa Medialab  

DOI： 10.22323/1.444.0899

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

A gamma-ray glow, a minute-lasting burst of high-energy photons from a thundercloud, was detected by ground-based apparatus at Kanazawa University, Japan, in a winter thunderstorm on 18 December 2018. The gamma-ray glow was quenched by a lightning flash within a brief time window of 40 ms. The lightning flash produced several low-frequency (LF) E-change pulses that were temporally coincident with the termination of the gamma-ray glow, and that were located within 0.5 km from the observation site by the Fast Antenna Lightning Mapping Array. The LF pulses had the same polarity as a positive cloud-to-ground current and a normal-polarity in-cloud current. Since this polarity is against the upward electric field for producing the gamma-ray glow (accelerating electrons to the ground), we infer that the glow was terminated by a normal-polarity in-cloud discharge activity between a middle negative layer and an upper positive layer.

DOI： 10.1029/2023JD038606

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Scopus

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Sissa Medialab  

DOI： 10.22323/1.444.1607

掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Research Letters  

Gamma-ray glows are observational evidence of relativistic electron acceleration due to the electric field in thunderclouds. However, it is yet to be understood whether such relativistic electrons contribute to the initiation of lightning discharges. To tackle this question, we started the citizen science “Thundercloud Project,” where we map radiation measurements of glows from winter thunderclouds along Japan's sea coast area. We developed and deployed 58 compact gamma-ray monitors at the end of 2021. On 30 December 2021, five monitors simultaneously detected a glow with its radiation distribution horizontally extending for 2 km. The glow terminated coinciding with a lightning flash at 04:08:34 JST, which was recorded by the two radio-band lightning mapping systems, FALMA and DALMA. The initial discharges during the preliminary breakdown started above the glow, that is, in vicinity of the electron acceleration site. This result provides one example of possible connections between electron acceleration and lightning initiation.

DOI： 10.1029/2023GL103612

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記述言語：英語  

Gamma-ray glows are observational evidence of relativistic electron acceleration due to the electric field in thunderclouds. However, it is yet to be understood whether such relativistic electrons contribute to the initiation of lightning discharges. To tackle this question, we started the citizen science “Thundercloud Project, ” where we map radiation measurements of glows from winter thunderclouds along Japan's sea coast area. We developed and deployed 58 compact gamma-ray monitors at the end of 2021. On 30 December 2021, five monitors simultaneously detected a glow with its radiation distribution horizontally extending for 2 km. The glow terminated coinciding with a lightning flash at 04:08:34 JST, which was recorded by the two radio-band lightning mapping systems, FALMA and DALMA. The initial discharges during the preliminary breakdown started above the glow, that is, in vicinity of the electron acceleration site. This result provides one example of possible connections between electron acceleration and lightning initiation.

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

Electric field of thunderclouds modifies components and energy spectra of the cosmic-ray air shower. In particular, thunderstorms accelerate charged particles, resulting in an enhancement of gamma-ray fluxes on the ground, known as a gamma-ray glow. This phenomenon has been observed in recent years by the Gamma-Ray Observation of Winter THunderclouds collaboration from winter thunderstorms in the Hokuriku area of Japan. The present work examines the ambient conditions required to produce spectral features of the previously detected gamma-ray glows, by using Monte Carlo simulations of particle interactions in the atmosphere. We focus on three parameters, the strength and length of the electric field, and the length of a null-field attenuation region below the electrified region. The average spectrum of observed gamma-ray glows in winter thunderstorms of Japan requires an electric field intensity close to 0.31 MV/m, slightly exceeding the Relativistic Runaway Electron Avalanche threshold of 0.284 MV/m. The vertical size of the electric field region should be comparable to 1 km. The estimated attenuation region size is 300–500 m, necessary to reduce the low-energy photon flux of the average gamma-ray glows. There is still a wide range of acceptable parameter sets with degeneracy to make a similar spectrum.

DOI： 10.1029/2022JD038246

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Scopus

掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We report on results of our upgraded Giant Metrewave Radio Telescope (uGMRT) observations for an early-stage merging galaxy cluster, CIZA J1358.9−4750 (CIZA1359), in Band-3 (300–500 MHz). We achieved the image dynamic range of ∼38000 using the direction dependent calibration and found a candidate of diffuse radio emission at 4σrms significance. The flux density of the candidate at 400 MHz, 24.04 ± 2.48 mJy, is significantly positive compared to noise, where its radio power, 2.40 × 1024 W Hz−1, is consistent with those of typical diffuse radio sources of galaxy clusters. The candidate is associated with a part of the X-ray shock front at which the Mach number reaches its maximum value of M ∼ 1.7. The spectral index (Fν ∝ να) of the candidate, α = −1.22 ± 0.33, is in agreement with an expected value derived from the standard diffusive shock acceleration (DSA) model. However, such a low Mach number with a short acceleration time would require seed cosmic rays supplied from active galactic nucleus (AGN) activities of member galaxies, as suggested in some other clusters. Indeed, we found seven AGN candidates inside the diffuse source candidate. Assuming the energy equipartition between magnetic fields and cosmic rays, the magnetic field strength of the candidate was estimated to be 2.1 μG. We also find head–tail galaxies and radio phoenixes or fossils near CIZA1359.

DOI： 10.1093/pasj/psac098

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Scopus

出版者・発行元：Publications of the Astronomical Society of Japan  

CIZA J1358.9−4750 is a nearby galaxy cluster in the early phase of a major merger. The two-dimensional temperature map using XMM-Newton EPIC-PN observation confirms the existence of a high-temperature region, which we call the “hot region,” in the “bridge region” connecting the two clusters. The ∼500 kpc wide region between the south-east and north-west boundaries also has higher pseudo-pressure compared to the unshocked regions, suggesting the existence of two shocks. The southern shock front is clearly visible in the X-ray surface brightness image and has already been reported by Kato et al. (2015, PASJ, 67, 71). The northern one, on the other hand, is newly discovered. To evaluate their Mach number, we constructed a three-dimensional toy merger model with overlapping shocked and unshocked components in the line of sight. The unshocked and pre-shock intracluster medium (ICM) conditions are estimated based on those outside the interacting bridge region, assuming point symmetry. The hot-region spectra are modeled with two-temperature thermal components, assuming that the shocked condition follows the Rankin–Hugoniot relation with the pre-shock condition. As a result, the shocked region is estimated to have a line-of-sight depth of ∼1 Mpc with a Mach number of ∼1.3 in the south-east shock and ∼1.7 in the north-west shock. The age of the shock waves is estimated to be ∼260 Myr. This three-dimensional merger model is consistent with the Sunyaev–Zel’dovich signal obtained using the Planck observation within the cosmic microwave background fluctuations. The total flow of the kinetic energy of the ICM through the south-east shock was estimated to be ∼2.2 × 1042 erg s−1. Assuming that 10% of this energy is converted into ICM turbulence, the line–of–sight velocity dispersion is calculated to be ∼200 km s−1, which is basically resolvable via upcoming high spectral resolution observations.

DOI： 10.1093/pasj/psac087

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arXiv

その他リンク： http://arxiv.org/pdf/2210.02145v2

出版者・発行元：Proceedings of Science  

Fast neutrons generated by the interaction between ions and the solar atmosphere are important observation problems to clarify the ion acceleration mechanism in the Sun, but so far neutrons have been detected from only 12 X-class solar flares in the highland on the ground due to the influence of atmospheric absorption. As for observations in space, SEDA-AP at the International Space Station continued to operate until 2018 and succeeded in neutron detection from 52 solar flares, but there are currently no dedicated space missions. In order to overcome this situation, we have been designing and developing 3U CubeSat and novel neutron/gamma-ray sensors since 2018 with the aim of performing satellite observations from outer space. The sensor consists of the multi-layered plastic scintillator bars readout with Si PM, which is a semiconductor photo-sensor, and detects fast neutrons from the tracks of ejected protons by elastic scattering. Furthermore, by placing GAGG scintillator arrays at the bottom, it is designed to be sensitive to gamma-rays based on the principle of the Compton camera. In this presentation, we will report on the scientific motivation and the development status of CubeSat and neutron/gamma-ray sensors.

Scopus

掲載種別：研究論文（国際会議プロシーディングス）  

Fast neutrons generated by the interaction between ions and the solar atmosphere are important observation problems to clarify the ion acceleration mechanism in the Sun, but so far neutrons have been detected from only 12 X-class solar flares in the highland on the ground due to the influence of atmospheric absorption. As for observations in space, SEDA-AP at the International Space Station continued to operate until 2018 and succeeded in neutron detection from 52 solar flares, but there are currently no dedicated space missions. In order to overcome this situation, we have been designing and developing 3U CubeSat and novel neutron/gamma-ray sensors since 2018 with the aim of performing satellite observations from outer space. The sensor consists of the multi-layered plastic scintillator bars readout with Si PM, which is a semiconductor photo-sensor, and detects fast neutrons from the tracks of ejected protons by elastic scattering. Furthermore, by placing GAGG scintillator arrays at the bottom, it is designed to be sensitive to gamma-rays based on the principle of the Compton camera. In this presentation, we will report on the scientific motivation and the development status of CubeSat and neutron/gamma-ray sensors.

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Research Letters  

Winter thunderstorms in Japan have been recognized as an ideal target to observe high-energy atmospheric phenomena thanks to low-charge-center cloud structures. During four winter seasons in Japan (from 2016 October to 2020 March), seven downward terrestrial gamma-ray flashes (TGFs) were detected by gamma-ray and broadband low-frequency (LF: 0.8–500 kHz) monitors. All the detected TGFs took place at the initial stage of lightning flashes. Based on the LF observation, the seven downward TGFs in the present study can be classified into two types: energetic-bipolar and small-bipolar types. Three of them are energetic-bipolar events, coincident with a high peak-current LF pulse that originates from a negative return stroke with a peak current larger than 100 kA. The others are small-bipolar events, followed by a negative bipolar LF pulse with a moderate peak current. Three of the four small-bipolar events are multi-pulse TGFs, while all of the energetic-bipolar events in this study are single-pulse TGFs.

DOI： 10.1029/2021GL097348

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Scopus

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021GL097348

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

Cosmic-ray shower, hitting the atmosphere all the time, includes high-energy electrons. Electric fields in thunderstorms accelerate these electrons so that they can reach farther distances with producing secondary electrons. The strong field above 0.284 MV m−1 causes the Relativistic Runaway Electron Avalanches (RREA) process with an exponential increase of electrons. Even with lower electric fields below this RREA threshold which are usually measured in thunderstorms, an increase in electrons' kinetic energy and production of secondary electrons can occur without avalanche processes, known as Modification Of Spectra (MOS) of the cosmic-ray shower. Both phenomena are related to observed gamma ray glow, which is bremsstrahlung emission from accelerated electrons in thunderstorms. We calculate an extended range and kinetic energy of electrons below the RREA threshold using an analytical evaluation and Geant4 Monte Carlo simulations. For example, at 0.280 MV m−1 slightly below the RREA threshold, 3 MeV electrons gain 100% of their original kinetic energy through the passage of the continuous slowing down approximation (CSDA) range defined at the null electric field, which is consistent with results in previous studies as the transition to the RREA process. Even at a lower field of 0.260 MV m−1, the energy recovery by the field allows an injected 20 MeV electron beam to extend its average electron range from 73 m, in the null field configuration, to 562 m. We have performed analytical calculation and Geant4 simulations of atmospheric electron behavior for initial electron energy of 0.1–100 MeV and an electric field below 0.290 MV m−1.

DOI： 10.1029/2021JD035958

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JD035958

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

The MeV band covers the physics of the lowest energy end of the non-thermal universe and nuclear reactions in metal synthesis and/or matters interacting with cosmic rays. Nevertheless, sensitivity in this band is still limited. Improving MeV sensitivity is one of the most important issues in modern astronomy. The soft gamma-ray detector (SGD) onboard the Hitomi satellite launched in 2016 was an innovative narrow field-of-view semiconductor Compton telescope (SCT), which aims at background reduction through deep active-shielding combined with SCT using Si and CdTe, a Si/CdTe-SCT. Although with a limited operation time, it is the sole SCT proven in orbit to date, and succeeded in detecting ∼ 100 keV polarization with only 5 ks exposure. Based on these achievements, we propose a new approach “narrow field-of-view Si/CdTe-SCT at balloon altitude”. At the altitude of 32-40 km, detectors do not suffer severe proton bomberment, which was one of the major contributor to the SGD background, while able to observe MeV gamma rays from the universe. Atmospheric gamma rays is non-negligible, but as it is stronger near horizon, narrowing the field-of-view and aiming around zenith will cut most of them. The detector loses wide field of view, but can be used as a probe in sub-MeV band. As the first step of this approach, we are planning a balloon experiment, miniSGD, to confirm the concept. It is very compact and not aiming at real observation, but has all the components integrated within the 40 × 40 × 50 cm3 volume, including detectors, electronics and the collimator. The Si/CdTe-SCT was made of a single layer of 0.5 mm thick double-sided Si strip detectors (DSSDs) and newly developed 2 mm thick CdTe double sided strip detectors (CdTe-DSDs), surrounded by nine units of 2-3 cm thick BGO scintillator crystals. The miniSGD experiment is to fly as a piggy-back payload in the 2023 Spring campaign of JAXA Ballooning team at Alice Springs, Australia. Technologies to be verified in miniSGD are also applicable to the future hard X-ray missions, such as the FORCE mission.

DOI： 10.1117/12.2628199

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

Xappl is a software framework written in Python to build pre-pipelines for the X-Ray Imaging and Spectroscopy Mission (XRISM) scheduled to be launched in the Japanese fiscal year 2022. Xappl chains software tasks in the order specified in configuration files in the INI format, enabling us to reduce the telemetry data to First FITS Files, which originate datasets ready for analysis. Since the functionalities of Xappl are highly generalized, it is reusable for future missions. In this paper, we present the design of Xappl and report the developmental progress of the pre-pipeline for XRISM.

DOI： 10.1117/12.2629316

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

The SOlar Neutron and Gamma-ray Spectroscopy (SONGS) mission is a 3U cubesat dedicated for detecting neutrons and gamma-rays associated with intense solar flares. Solar neutron observations have not been in progress because ground-based observations are affected by attenuation in the Earth atmosphere, and there is no dedicated mission in space at present. Hence, we are now developing in collaboration between science and engineering people at universities, and preparing for launch around 2024 during the next solar maximum. The SONGS carries a novel radiation detector which consists of multi-layered plastic scintillator bars and GAGG(Ce) scintillator array so that it can determine energies for both neutrons and gamma-rays. In total 704 signals from Silicon photo-multipliers (SiPMs) are processed by 45 ASICs with very low power consumption, and realized within limited resources. In this presentation, we will describe scientific motivation, mission and instrument overview, and results from the bread-board model (BBM).

DOI： 10.1117/12.2629131

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出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

We present the detector performance and early science results from GRBAlpha, a 1U CubeSat mission, which is a technological pathfinder to a future constellation of nanosatellites monitoring gamma-ray bursts (GRBs). GRBAlpha was launched in March 2021 and operates on a 550 km altitude sun-synchronous orbit. The gamma-ray burst detector onboard GRBAlpha consists of a 75×75×5 mm CsI(Tl) scintillator, read out by a dual-channel multi-pixel photon counter (MPPC) setup. It is sensitive in the a1/430-900 keV range. The main goal of GRBAlpha is the in-orbit demonstration of the detector concept, verification of the detector's lifetime, and measurement of the background level on low-Earth orbit, including regions inside the outer Van Allen radiation belt and in the South Atlantic anomaly. GRBAlpha has already detected five, both long and short, GRBs and two bursts were detected within a time-span of only 8 hours, proving that nanosatellites can be used for routine detection of gamma-ray transients. For one GRB, we were able to obtain a high resolution spectrum and compare it with measurements from the Swift satellite. We find that, due to the variable background, the time fraction of about 67% of the low-Earth polar orbit is suitable for gamma-ray burst detection. One year after launch, the detector performance is good and the degradation of the MPPC photon counters remains at an acceptable level. The same detector system, but double in size, was launched in January 2022 on VZLUSAT-2 (3U CubeSat). It performs well and already detected three GRBs and two solar flares. Here, we present early results from this mission as well.

DOI： 10.1117/12.2629332

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

CFRP is a composite material composed of carbon fiber and resin. CFRP is commonly applied to the aerospace industry which requires lightweight and intensity. Thanks to superior formability of CFRP, we can form shape of Wolter-1 optics, which consists of paraboloid and hyperboloid, to a monolithic substrate. Since the surface roughness of CFRP substrate is a few microns, it is required to make the smooth surface for reflecting X-rays on the CFRP substrate. We have developed a new method of shaping the reflective surface by pasting thin sheet-glass with 50~100 µm thick onto the CFRP substrate. The surface roughness of the thin sheet-glass was measured to about 0.4 nm by Zygo. Our CFRP mirror is a candidate for backup mirrors in the FORCE mission, and are being developed for balloon-borne experiments planned in the near future. Current image quality of our CFRP mirror was measured to be about 60-120 arcsec by illuminating an X-ray pencil beam at the ISAS beam line. In order to achieve a high imaging quality less than 15 arcsec, we will improve the CFRP mirror surface using both the replica method, and an ultra-precision mold processed with a shape error of 0.1 µm or less. The mold will be completed in the summer of 2022. We report on the current status of the development of the CFRP mirrors.

DOI： 10.1117/12.2629705

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Research  

In 2015, the Gamma-Ray Observation of Winter Thunderstorms (GROWTH) collaboration launched a mapping observation campaign for high-energy atmospheric phenomena related to thunderstorms and lightning discharges. This campaign has developed a detection network of gamma rays with up to 10 radiation monitors installed in the cities of Kanazawa and Komatsu, Ishikawa Prefecture, Japan, where low-charge-center winter thunderstorms frequently occur. During four winter seasons from October 2016 to April 2020, a total of 70 gamma-ray glows, i.e., minute-lasting bursts of gamma rays originating from thunderclouds, were detected. Their average duration is 58.9 s. Among the detected events, 77% were observed at night. The gamma-ray glows can be classified into temporally symmetric, temporally asymmetric, and lightning-terminated types based on their count-rate histories. An averaged energy spectrum of the gamma-ray glows is well fitted with a power-law function with an exponential cutoff, whose photon index, cutoff energy, and flux are 0.613±0.009 MeV, 4.68±0.04 MeV, and (1.013±0.003)×10-5 erg cm-2s-1 (0.2-20.0 MeV), respectively. The present paper provides a catalog of gamma-ray glows and their statistical analysis detected during winter thunderstorms in the Kanazawa and Komatsu areas.

DOI： 10.1103/PhysRevResearch.3.043117

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevResearch.3.043117/fulltext

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

Around 17:00 on January 12, 2020 (UTC), radiation detectors installed at two locations with a 1.35 km separation in Kanazawa City, Japan, captured a total of four gamma-ray enhancements. The first pair was simultaneously observed at the two locations at 17:03 and were abruptly terminated by a lightning discharge. The remaining two enhancements were also nearly simultaneously observed (Formula presented.) 3 min later, and one of them was also terminated by another lightning discharge. At the last termination, a downward terrestrial gamma-ray flash and a negative energetic in-cloud pulse were observed. Both pairs were associated with thundercloud cells. In the first pair, simultaneous detection in two locations 1.35 km apart suggests either a gamma-ray glow emerged in-between and time variability of its intensity were directly observed or there were two (or more) gamma-ray glows in the cell which reached the two detectors coincidentally. In the latter pair, the peak time in the downwind detector was (Formula presented.) 40 s later than that of the upwind detector. If the irradiation region moved with the cell, it would have taken ∼110 s. The discrepancy suggests either the glow moved 2.5 times faster than the cell or there were two (or more) glows in the cell. Also, the fact that the thunderstorm cell hosting the latter glows experienced the lightning discharge (Formula presented.) 3 min before suggests that the strong electric field in the cell can develop within a few minutes.

DOI： 10.1029/2021JD034543

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出版者・発行元：Proceedings of Science  

Since 2006, The Gamma Ray Observation of Winter Thunderclouds (GROWTH) collaboration has operated radiation measurement networks at the coastal area of Japan sea. The area is famous for its frequent occurrence of winter thunderstorms. We aims at elucidating how particles in lightning and thunderclouds are accelerated to relativistic energies. More than 10-years observations reveal that there are two types of radiation bursts associated with winter thunderstorms. One is a "long burst" or a "gamma-ray glow" lasting for a few tens of seconds to a few minutes. The other is a "short burst" in association with lightning. In order to expand the observational network, we have developed a small type of a radiation detector. In this paper, we focus on recent several findings obtained by the new detectors. One is a combination of a short burst and a long one, showing simultaneous detection of prompt gamma rays extending to ∼10 MeV and the 511-keV annihilation ones. These gamma-ray signals demonstrate the occurrence of photonuclear reactions in lightning. Another is an event that a gamma-ray glow suddenly ceased just prior to lightning, suggesting a relation between lightning and the two types of radiation bursts. On the basis of these results, we discuss the production mechanism of gamma rays related to thunderstorms and the lightning initiation problem.

Scopus

出版者・発行元：Proceedings of Science  

Solar neutron observations are very important on understanding of particle acceleration mechanism in the Sun. However, previous ground-based observations with large area telescope (∼10 m2)at high latitude are not sensitive to solar neutrons due to attenuation in the earth atmosphere and roughly 10 detection since its discovery in 1980. From space, the SEDA-AP instrument with much smaller area (100 cm2) onboard the International Space Station (ISS) monitored solar neutrons including charged particles, and successfully detected more than 30 detection since its launch in 2009. Unfortunately the SEDA-AP operation was stopped on March 2018. To overcome situation for no mission dedicated for solar neutrons, we have designed and developed a solar neutron and gamma-ray detector for a 3U cubesat with a size of 30×10×10 cm. Actually we launched the 50-kg class ChubuSat-2 satellite for solar neutron observations on February 2016, and have now been adjusting it to a 3U cubesat application. The solar neutron and gamma-ray detector consists of multi-layered plastic scintillator bars, and GAGG(Ce) scintillator array, and both of them are read out with silicon photo-multipliers (Si PMs). More than 600 signals from Si PMs are processed by ASICs. In this paper, we will describe details of the detector and performance of its breadboard model (BBM).

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

X-Ray Imaging and Spectroscopy Mission (XRISM) is an x-ray astronomical mission led by the Japan Aerospace Exploration Agency (JAXA) and National Aeronautics and Space Administration (NASA), with collaboration from the European Space Agency (ESA) and other international participants, that is planned for launch in 2022 (Japanese fiscal year), to quickly restore high-resolution x-ray spectroscopy of astrophysical objects using the microcalorimeter array after the loss of Hitomi satellite. In order to enhance the scientific outputs of the mission, the Science Operations Team (SOT) is structured independently from the Instrument Teams (ITs) and the Mission Operations Team. The responsibilities of the SOT are divided into four categories: (1) guest observer program and data distributions, (2) distribution of analysis software and the calibration database, (3) guest observer support activities, and (4) performance verification and optimization activities. Before constructing the operations concept of the XRISM mission, lessons on the science operations learned from past Japanese x-ray missions (ASCA, Suzaku, and Hitomi) are reviewed, and 15 kinds of lessons are identified by categories, such as lessons on the importance of avoiding non-public ("animal") tools, coding quality of public tools in terms of the engineering viewpoint and calibration accuracy, tight communications with ITs and operations teams, and well-defined task division between scientists and engineers. Among these lessons, (a) the importance of early preparation of the operations from the ground stage, (b) construction of an independent team for science operations separate from the instrument development, and (c) operations with well-defined duties by appointed members are recognized as key lessons for XRISM. Based on this, (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. Based on this operations concept, the detailed plan of the science operations is designed as follows. The science operations tasks are shared among Japan, the USA, and Europe and are performed by three centers: the Science Operations Center (SOC) at JAXA, the Science Data Center (SDC) at NASA, and European Space Astronomy Centre (ESAC) at the 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, and prepipeline data processing. The SDC covers tasks regarding data calibration processing (pipeline processing) and maintenance of analysis tools. The data-archive and user-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 science operations are defined and prepared before launch. This information is expected to be helpful for the construction of science operations of future x-ray missions.

DOI： 10.1117/1.JATIS.7.3.037001

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記述言語：日本語   出版者・発行元：Progress of Theoretical and Experimental Physics  

The Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is a future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could have been produced during the inflationary period right after the birth of the Universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the Universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry-Pérot Michelson interferometers with an arm length of 1000 km. Three DECIGO clusters will be placed far from each other, and the fourth will be placed in the same position as one of the other three to obtain correlation signals for the detection of primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder for DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand multi-messenger astronomy.

DOI： 10.1093/ptep/ptab019

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Research Letters  

During three winter seasons from November 2016 to March 2019, 11 gamma-ray glows were detected at a single observation site of our ground-based gamma-ray monitoring network in Kanazawa, Japan. These events are analyzed with observations of an X-band radar network, a ceilometer, a disdrometer, and a weather monitor. All the detected glows were connected to convective high-reflectivity regions of more than 35 dBZ, developed up to an altitude of >2 km. They were also accompanied by heavy precipitation of graupels. Therefore, graupels in the lower layer of thunderclouds that correspond to high-reflectivity regions can form strong electric fields producing gamma-ray glows. Also, these events are compared with a limited sample of nondetection cases, but no significant differences in meteorological conditions were found between detection and nondetection cases in the present study.

DOI： 10.1029/2020GL091910

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL091910

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

In recent years, the number of CubeSats (U-class spacecrafts) launched into space has increased exponentially marking the dawn of the nanosatellite technology. In general, these satellites have a much smaller mass budget compared to conventional scientific satellites, which limits shielding of scientific instruments against direct and indirect radiation in space. We present a simulation framework to quantify the signal in large field-of-view gamma-ray scintillation detectors of satellites induced by x-ray/gamma-ray transients, by taking into account the response of the detector. Furthermore, we quantify the signal induced by x-ray and particle background sources at a Low-Earth Orbit outside South Atlantic Anomaly and polar regions. Finally, we calculate the signal-to-noise ratio (SNR) taking into account different energy threshold levels. Our simulation can be used to optimize material composition and predict detectability of various astrophysical sources by CubeSats. We apply the developed simulation to a satellite belonging to a planned CAMELOT CubeSat constellation. This project mainly aims to detect short and long gamma-ray bursts (GRBs) and as a secondary science objective, to detect soft gamma-ray repeaters (SGRs) and terrestrial gamma-ray flashes (TGFs). The simulation includes a detailed computer-aided design model of the satellite to take into account the interaction of particles with the material of the satellite as accurately as possible. Results of our simulations predict that CubeSats can complement the large space observatories in high-energy astrophysics for observations of GRBs, SGRs, and TGFs. For the detectors planned to be on board the CAMELOT CubeSats, the simulations show that detections with SNR of at least 9 for median GRB and SGR fluxes are achievable.

DOI： 10.1117/1.JATIS.7.2.028004

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER  

We report the radiation damage results of two new types of Multi-Pixel Photon Counter (MPPC) under the 200 MeV proton beam, for cosmic gamma-ray observations with CubeSats. The new MPPCs, S13360-6050CS and S14160-6050HS, have recently become commercially available by Hamamatsu Photonics K.K. (HPK). After 100 rad irradiation, the dark current increased by a factor of similar to 100 and the threshold energy of gamma-ray detection by CsI scintillator increased, but S14160-6050HS was less degraded. We then confirmed the annealing effects of the dark current and threshold energy for both. The decrease rate of the dark current in both MPPCs were similar to those in the previous works. At 20 degrees C, the threshold energies of both MPPCs reduced by several tens of percent after irradiation, but below 0 degrees C, the threshold energy of S14160-6050HS was not significantly lowered. We also confirmed that annealing began before one month post-irradiation.

DOI： 10.1016/j.nima.2020.164673

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

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.

DOI： 10.1117/12.2560861

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

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.

DOI： 10.1117/12.2560840

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

The X-Ray Imaging and Spectroscopy Mission (XRISM) is the successor to the 2016 Hitomi mission that ended prematurely. Like Hitomi, the primary science goals are to examine astrophysical problems with precise high-resolution X-ray spectroscopy. XRISM promises to discover new horizons in X-ray astronomy. XRISM carries a 6 x 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly and a co-aligned X-ray CCD camera that covers the same energy band over a large field of view. XRISM utilizes Hitomi heritage, but all designs were reviewed. The attitude and orbit control system were improved in hardware and software. The number of star sensors were increased from two to three to improve coverage and robustness in onboard attitude determination and to obtain a wider field of view sun sensor. The fault detection, isolation, and reconfiguration (FDIR) system was carefully examined and reconfigured. Together with a planned increase of ground support stations, the survivability of the spacecraft is significantly improved.

DOI： 10.1117/12.2565812

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

CFRP is a composite material composed of carbon fiber and resin. CFRP is commonly applied to the aerospace industry which requires lightweight and intensity. Thanks to superior formability of CFRP, we can form shape of Wolter-1 optics, which consists of paraboloid and hyperboloid, to a monolithic substrate. Since the surface roughness of a CFRP substrate is a few µm, we have to make the smooth surface for reflecting X-rays on the CFRP substrate. We have developed a new method of shaping the reflective surface instead of the replica method used in lightweight X-ray mirrors such as Astro-H. In the new method, the reflective surface is formed by pasting thin sheet-glasses with 100 µm thick onto the CFRP substrate. The thin sheet-glass has a surface roughness about 0.4 nm as measured by Zygo. We fabricated a CFRP mirror pasting thin sheet-glasses, and then coated tungsten on the mirror in June 2020. The figure error (s) of the CFRP mirror was achieved to be about 1-2 µm by stacking the CFRP mirror on the housing module. X-ray imaging quality of the CFRP mirror was measured at Spring-8 in July 2020. The half-power diameter of the CFRP mirror was estimated to be about 150 arcsec, which was nearly equal to the prediction from a distribution of the slope error deduced from the surface profile. We describe a future plan to improve the image quality of the CFRP mirror.

DOI： 10.1117/12.2561890

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

GRBAlpha is a 1U CubeSat mission with an expected launch date in the first half of 2021. It carries a 75 × 75 × 5 mm CsI(Tl) scintillator, read out by a dual-channel multi-pixel photon counter (MPPC) setup, to detect gamma-ray bursts (GRBs). The GRB detector is an in-orbit demonstration for the detector system on the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT) mission. While GRBAlpha provides 1/8th of the expected effective area of CAMELOT, the comparison of the observed light curves with other existing GRB monitoring satellites will allow us to validate the core idea of CAMELOT, i.e. the feasibility of timing-based localization.

DOI： 10.1117/12.2561351

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記述言語：英語   出版者・発行元：一般社団法人 日本航空宇宙学会  

<p>Solar neutron observations are very important for understanding of nucleon acceleration mechanism in solar flares, but there are only a few tens of detection since the discovery in 1980. This is because solar neutron observations have been mainly carried out from not space but the ground with insufficient sensitivity. For microsatellite applications, we have designed very compact and high sensitive solar neutron and gamma-ray spectrometer utilizing a novel photo-sensor Silicon photo-multiplier. This paper describes concept, design and performance of our detector for micro/nanosatellite applications.</p>

DOI： 10.2322/tastj.19.354

CiNii Research

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPIE  

DOI： 10.1117/12.2560928

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPIE  

DOI： 10.1117/12.2561341

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

We report simulation results of photonuclear reactions in the atmosphere triggered by a downward terrestrial gamma ray flash in lightning. Possible channels of reactions in the atmosphere and their cross-sections are verified with the ENDF/B-VII.1 library. Monte Carlo simulations with two stages are then performed with the Geant4 framework. In the first stage, electrons following the relativistic runaway electron avalanche spectrum are produced in a mass model of the atmosphere, and production of photoneutrons and β+-decay nuclei is calculated based on the nuclear data library. In total 1 × 1013 neutrons and 4 × 1012 β+-decay nuclei are produced by 1018 energetic electrons above 1 MeV. In the second stage, propagation of the photoneutrons and positrons from the β+-decay nuclei in the previous stage is calculated. As a result, we model on-ground distributions of fluxes and energy spectra for neutrons, neutron-related gamma rays, and annihilation ones. The simulation model is to be compared with photonuclear events detected in low-charge-center winter thunderstorms.

DOI： 10.1029/2020JD033193

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

During a winter thunderstorm on 6 February 2017 in Japan, photonuclear reactions such as 14N(γ, n)13N were triggered by a downward terrestrial gamma-ray flash (TGF), as reported by Enoto et al. (2017, https://doi.org/10.1038/nature24630). In the present paper, we compare the observation with a simulation model of downward TGFs and subsequent photonuclear reactions constructed by the first paper of the series and Wada, Enoto, Nakazawa, et al. (2019, https://doi.org/10.1103/physrevlett.123.061103). The observation and model consist of three components: annihilation gamma rays from positrons produced by β+-decay nuclei, deexcitation gamma rays originating from neutron captures, and radiation doses by TGF photons. Each component of the observation is reproduced by the simulation model, and we constrain a relation between the number of avalanche electrons and their production altitude of the downward TGF. The constraints by three components match within an order of magnitude. The downward TGF is estimated to comprise (0.5–2.5) × 1019 avalanche electrons above 1 MeV produced at an altitude of 1.4–2.7 km. Despite differences in altitude, direction, and season, downward TGFs in winter thunderstorms are thought to have the same mechanism of electron acceleration and multiplication in lightning as TGFs observed by in-orbit satellites.

DOI： 10.1029/2020JD033194

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

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.

DOI： 10.1117/1.JATIS.6.4.046003

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Progress of Theoretical and Experimental Physics  

We have designed, developed, and deployed a distributed sensor network to observe high-energy ionizing radiation, primarily gamma rays, from winter thunderclouds and lightning in coastal areas of Japan. Starting in 2015, we have installed a total of more than 15 ground-based detector systems in Ishikawa Prefecture and Niigata Prefecture, and accumulated 551 days of observation time in four winter seasons from late 2015 to early 2019. In this period, our system recorded 51 gamma-ray radiation events from thundercloud and lightning. Highlights of the science results obtained from this unprecedented amount of data include the discovery of photonuclear reaction in lightning which produces neutrons and positrons along with gamma rays, and deeper insights into the life cycle of a particle-acceleration and gamma-ray-emitting region in a thundercloud. The present paper reviews the objective, methodology, and results of our experiment, with an emphasis on its instrumentation.

DOI： 10.1093/ptep/ptaa115

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astronomy and Astrophysics  

Based mainly on X-ray observations, we study the interactions between the intracluster medium (ICM) in clusters of galaxies and their member galaxies. Through (magneto)hydrodynamic and gravitational channels, moving galaxies are expected to drag the ICM around them, and then transfer some fraction of their dynamical energies on cosmological timescales to the ICM. This hypothesis is in line with several observations, including the possible cosmological infall of galaxies toward the cluster center, found over redshifts of z? ∼? 1 to z? ∼? 0. Further assuming that the energy lost by these galaxies is first converted into ICM turbulence and then dissipated, this picture can explain the subsonic and uniform ICM turbulence, measured with Hitomi in the core region of the Perseus cluster. The scenario may also explain several other unanswered problems regarding clusters of galaxies, such as what prevents the ICM from underoing the expected radiative cooling, how the various mass components in nearby clusters have attained different radial distributions, and how a thermal stability is realized between hot and cool ICM components that co-exist around cD galaxies. This view is also considered to pertain to the general scenario of galaxy evolution, including their environmental effects.

DOI： 10.1051/0004-6361/201936437

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

During a winter thunderstorm on 24 November 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, Gd155 and Gd157, have large cross sections of neutron captures to thermal neutrons such as Gd155(n,γ)Gd156 and Gd157(n,γ)Gd158. Deexcitation gamma rays from Gd156 and Gd158 are self-absorbed in the scintillation crystals, and make spectral-line features which can be distinguished from other non-neutron signals. The neutron burst lasted for ∼100 ms, and neutron fluences are estimated to be >52 and >31 neutrons cm-2 at two observation points inside the power station. Gadolinium orthosilicate scintillators work as valid detectors for thermal neutrons in lightning.

DOI： 10.1103/PhysRevD.101.102007

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.101.102007/fulltext

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Atmospheres  

During 2017–2018 winter operation of the Gamma-Ray Observation of Winter Thunderclouds experiment in Japan, two downward terrestrial gamma-ray flashes (TGFs) that triggered atmospheric photonuclear reactions were detected. They took place during winter thunderstorms on 5 December 2017 and 9 January 2018 at Kanazawa, Ishikawa Prefecture, Japan. Each event coincided with an intracloud/intercloud discharge, which had a negative-polarity peak current higher than 150 kA. Their radio waveforms in the low-frequency band are categorized as a distinct lightning type called “energetic in-cloud pulse” (EIP). Negative-polarity EIPs have been previously suggested to be highly associated with downward TGFs, and the present observations provide evidence of the correlation between them for the first time. Furthermore, both of the downward TGFs followed “gamma-ray glows,” minute-lasting high-energy emissions from thunderclouds. It is suggested that the negative EIPs took place with downward propagating negative leaders or upward positive ones developed in highly electrified regions responsible for the gamma-ray glows.

DOI： 10.1029/2019JD031730

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

The timing-based localization, which utilize the triangulation principle with the different arrival time of gammaray photons, with a fleet of Cubesats is a unique and powerful solution for the future all-sky gamma-ray observation, which is a key for identification of the electromagnetic counterpart of the gravitational wave sources. The Cubesats Applied for MEasuring and Localising Transients (CAMELOT) mission is now being promoted by the Hungarian and Japanese collaboration with a basic concept of the nine Cubesats constellations in low earth orbit. The simulation framework for estimation of the localization capability has been developed including orbital parameters, an algorithm to estimate the expected observed profile of gamma-ray photons, finding the peak of the cross-correlation function, and a statistical method to find a best-fit position and its uncertainty. It is revealed that a degree-scale localization uncertainty can be achieved by the CAMELOT mission concept for bright short gamma-ray bursts, which could be covered by future large field of view ground-based telescopes. The new approach utilizing machine-learning approach is also investigated to make the procedure automated for the future large scale constellations. The trained neural network with 106 simulated light curves generated by the artificial short burst templates successfully predicts the time-delay of the real light curve and achieves a comparable performance to the cross-correlation algorithm with full automated procedures.

DOI： 10.1117/12.2562253

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.75.1.0_523

記述言語：英語   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

Using archival data from Suzaku, XMM-Newton, and NuSTAR, nine representative ultra-luminous X-ray sources (ULXs) in nearby galaxies were studied. Their X-ray spectra were all reproduced with a multicolour disc emission model plus its Comptonization. However, the spectral shapes of individual sources changed systematically depending on the luminosity, and defined three typical spectral states. These states differ either in the ratio between the Comptonizing electron temperature and the innermost disc temperature, or in the product of Compton y-parameter and fraction of the Comptonized disc photons. The luminosity range at which a particular state emerges was found to scatter by a factor of up to 16 among the eight ULXs. By further assuming that the spectral state is uniquely determined by the Eddington ratio, the sample ULXs are inferred to exhibit a similar scatter in their masses. This gives a model-independent support to the interpretation of ULXs in terms of relatively massive black holes. None of the spectra showed noticeable local structures. Especially, no Fe K-shell absorption/emission lines were detected, with upper limits of 30-40 eV in equivalent width from the brightest three among the sample: NGC 1313 X-1, Holmberg IX X-1, and IC 342 X-1. These properties disfavour ordinary mass accretion from a massive companion star, and suggest direct Bondi-Hoyle accretion from dense parts of the interstellar medium.

DOI： 10.1093/mnras/stz2139

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Modern Physics D  

DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) is a future Japanese space gravitational-wave antenna. The most important objective of DECIGO, among various sciences to be aimed at, is to detect gravitational waves coming from the inflation of the universe. DECIGO consists of four clusters of spacecraft, and each cluster consists of three spacecraft with three Fabry-Perot Michelson interferometers. As a pathfinder mission of DECIGO, B-DECIGO will be launched, hopefully in the 2020s, to demonstrate technologies necessary for DECIGO as well as to lead to fruitful multimessenger astronomy. B-DECIGO is a small-scale or simpler version of DECIGO with the sensitivity slightly worse than that of DECIGO, yet good enough to provide frequent detection of gravitational waves.

DOI： 10.1142/S0218271818450013

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

During a winter thunderstorm on 24 November 2017, a strong burst of gamma rays with energies up to ∼10 MeV was detected coincident with a lightning discharge, by scintillation detectors installed at the Kashiwazaki-Kariwa Nuclear Power Station at sea level in Japan. The burst had a subsecond duration, which is suggestive of photoneutron production. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-frequency radio pulse. These bunches were separated by 0.7-1.5 ms, with a duration of 1 ms each. Thus, the present burst may be considered as a "downward" terrestrial gamma-ray flash (TGF), which is analogous to upgoing TGFs observed from space. Although the scintillation detectors were heavily saturated by these bunches, the total dose associated with them was successfully measured by ionization chambers, employed by nine monitoring posts surrounding the power plant. From this information and Monte Carlo simulations, the present downward TGF is suggested to have taken place at an altitude of 2500±500 m, involving 8-4+8×1018 avalanche electrons with energies above 1 MeV. This number is comparable to those in upgoing TGFs.

DOI： 10.1103/PhysRevLett.123.061103

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PubMed

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.123.061103/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

This study presents a background estimation for the CubeSats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all-sky monitoring and timing-based localization of gamma ray transients with precise localization capability at low Earth orbits. CAMELOT will allow us to observe and precisely localize short gamma ray bursts (GRBs) associated with kilonovae, long GRBs associated with core-collapse massive stars, magnetar outbursts, terrestrial gamma ray flashes, and gamma ray counterparts to gravitational wave sources. A fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multipixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and minimize the effect of the radiation damage of MPPCs.

DOI： 10.1002/asna.201913673

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記述言語：日本語   出版者・発行元：Publications of the Astronomical Society of Japan  

We have systematically studied the spectral properties of 302 localized gamma-ray bursts (GRBs) observed by the Suzaku wide-band all-sky monitor (WAM) from 2005 August to 2010 December. The energy spectra in the 100-5000 keV range integrated over the entire emission and the 1 s peak were fitted by three models: a single power law, a power law with an exponential cutoff (CPL), and the GRB Band function (GRB). Most of the burst spectra were well fitted by a single power law. The average photon index α was -2.11 and -1.73 for long and short bursts, respectively. For the CPL and GRB models, the low-energy and high-energy photon indices (α and β) for the entire emission spectra were consistent with previous measurements. The averages of the α and β were -0.90 and -2.65 for long-duration GRBs, while the average α was -0.55 and the β was not well constrained for short-duration GRBs. However, the average peak energy Epeak was 645 and 1286 keV for long- and short-duration GRBs respectively, which are higher than previous Fermi/GBM measurements (285 keV and 736 keV). The α and Epeak of the 1 s peak spectra were larger, i.e., the spectra were harder, than the total fluence spectra. Spectral simulations based on Fermi-GBM results suggest that the higher Epeaks measured by the Suzaku WAM could be due to detector selection bias, mainly caused by the limited energy range above 100 keV.

DOI： 10.1093/pasj/psz054

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Communications Physics  

Two types of high-energy events have been detected from thunderstorms. One is “terrestrial gamma-ray flashes” (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting “gamma-ray glows”. Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for ~100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within ~1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF.

DOI： 10.1038/s42005-019-0168-y

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  

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.

DOI： 10.1016/j.nima.2018.09.114

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  

We are designing a fleet of nanosatellites to perform accurate position determinations of short-duration gamma-ray bursts by measuring arrival time differences. To achieve sufficient photon statistics to measure the arrival times precisely under the severe limitations of size, mass and power consumption, we propose the use of large-area CsI(Tl) scintillators which provide a high light output and the use of a small-sized multipixel photon counters (MPPC), a kind of SiPM, that have low power consumption. We plan to use one of the latest-model MPPCs provided by Hamamatsu Photonics, namely, S13360-6050CS, which has an active area of 6×6 mm2. We have compared the performance of two scintillators of different sizes (150×75×5 mm3 and 100×75×5 mm3); the bigger one is the maximum size that can be mounted on a three-unit satellite, according to CubeSat standards. We have found that the light yield of the bigger scintillator is lower than that of the smaller one, but the difference is only approximately 13%, and each has an energy threshold of ∼10 keV at 25∘C. We have tested one- and two-MPPC readout and confirmed the same energy thresholds. The light yield for the two-MPPC readout is 1.4 times as high as that for the one-MPPC readout. We have also examined the position dependence of the light yield by using radiation from a 241Am (59.5 keV) source, and confirmed that uniformity was improved, and energy resolution got better by ∼7% for two-MPPC readout.

DOI： 10.1016/j.nima.2018.08.039

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

Archival NuSTAR data of the magnetar 4U 0142+61, acquired in 2014 March for a total time span of 258 ks, were analyzed. This is to reconfirm the 55 ks modulation in the hard X-ray pulse phases of this source, found with a Suzaku observation in 2009 (Makishima et al.,2014, Phys. Rev. Lett., 112, 171102). Indeed, the 10-70 keV X-ray pulsation, detected with NuSTAR at 8.68917 s, was found to be also phase-modulated (at >98% confidence) at the same ∼55 ks period, or half that value. Furthermore, a brief analysis of another Suzaku data set of 4U 0142+61, acquired in 2013, reconfirmed the same 55 ks phase modulation in the 15-40 keV pulses. Thus, the hard X-ray pulse-phase modulation was detected with Suzaku (in 2009 and 2013) and NuSTAR (in 2014) at a consistent period. However, the modulation amplitude varied significantly; A ∼ 0.7 s with Suzaku (in 2009), A ∼ 1.2 s with Suzaku (in 2013), and A ∼ 0.17 s with NuSTAR. In addition, the phase modulation properties detected with NuSTAR differed considerably between the first 1/3 and the latter 2/3 of the observation. In energies below 10 keV, the pulse-phase modulation was not detected with either Suzaku or NuSTAR. These results reinforce the view of Makishima et al. (2014, Phys. Rev. Lett., 112, 171102); the neutron star in 4U 0142+61 keeps free precession, under a slight axial deformation due probably to ultra-high toroidal magnetic fields of ∼10 16 G. The wobbling angle of precession should remain constant, but the pulse-phase modulation amplitude varies on time scales of months to years, presumably as asymmetry of the hard X-ray emission pattern around the star's axis changes.

DOI： 10.1093/pasj/psy129

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出版者・発行元：Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)  

DOI： 10.1007/978-3-030-34175-6_19

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記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of Science  

Solar neutron observations are very important on understanding of particle acceleration mechanism in the Sun. However, previous ground-based observations with large area telescope (~10 m2)at high latitude are not sensitive to solar neutrons due to attenuation in the earth atmosphere and roughly 10 detection since its discovery in 1980. From space, the SEDA-AP instrument with much smaller area (100 cm2) onboard the International Space Station (ISS) monitored solar neutrons including charged particles, and successfully detected more than 30 detection since its launch in 2009. Unfortunately the SEDA-AP operation was stopped on March 2018. To overcome situation for no mission dedicated for solar neutrons, we have designed and developed a solar neutron and gamma-ray detector for a 3U cubesat with a size of 30×10×10 cm. Actually we launched the 50-kg class ChubuSat-2 satellite for solar neutron observations on February 2016, and have now been adjusting it to a 3U cubesat application. The solar neutron and gamma-ray detector consists of multi-layered plastic scintillator bars, and GAGG(Ce) scintillator array, and both of them are read out with silicon photo-multipliers (Si PMs). More than 600 signals from Si PMs are processed by ASICs. In this paper, we will describe details of the detector and performance of its breadboard model (BBM).

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of Science  

Since 2006, The Gamma Ray Observation of Winter Thunderclouds (GROWTH) collaboration has operated radiation measurement networks at the coastal area of Japan sea. The area is famous for its frequent occurrence of winter thunderstorms. We aims at elucidating how particles in lightning and thunderclouds are accelerated to relativistic energies. More than 10-years observations reveal that there are two types of radiation bursts associated with winter thunderstorms. One is a "long burst" or a "gamma-ray glow" lasting for a few tens of seconds to a few minutes. The other is a "short burst" in association with lightning. In order to expand the observational network, we have developed a small type of a radiation detector. In this paper, we focus on recent several findings obtained by the new detectors. One is a combination of a short burst and a long one, showing simultaneous detection of prompt gamma rays extending to ~10 MeV and the 511-keV annihilation ones. These gamma-ray signals demonstrate the occurrence of photonuclear reactions in lightning. Another is an event that a gamma-ray glow suddenly ceased just prior to lightning, suggesting a relation between lightning and the two types of radiation bursts. On the basis of these results, we discuss the production mechanism of gamma rays related to thunderstorms and the lightning initiation problem.

Scopus

記述言語：日本語   出版者・発行元：Publications of the Astronomical Society of Japan  

We present the results from the Hitomi Soft Gamma-ray Detector (SGD) observation of the Crab nebula. The main part of SGD is a Compton camera, which in addition to being a spectrometer, is capable of measuring polarization of gamma-ray photons. The Crab nebula is one of the brightest X-ray/gamma-ray sources on the sky, and the only source from which polarized X-ray photons have been detected. SGD observed the Crab nebula during the initial test observation phase of Hitomi. We performed data analysis of the SGD observation, SGD background estimation, and SGD Monte Carlo simulations and successfully detected polarized gamma-ray emission from the Crab nebula with only about 5 ks exposure time. The obtained polarization fraction of the phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1%±10.6%), and the polarization angle is 110°.7 + 13°.2/-13°.0 in the energy range of 60.160 keV (the errors correspond to the 1 σ deviation). The confidence level of the polarization detection was 99.3%. The polarization angle measured by SGD is about one sigma deviation with the projected spin axis of the pulsar, 124°.0 ± 0°.0.1.

DOI： 10.1093/pasj/psy118

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Research Letters  

An on-ground observation program for high energy atmospheric phenomena in<br />
winter thunderstorms along Japan Sea has been performed via measurements of<br />
gamma-ray radiation, atmospheric electric field and low-frequency radio band.<br />
On February 11, 2017, the radiation detectors recorded gamma-ray emission<br />
lasting for 75 sec. The gamma-ray spectrum extended up to 20 MeV and was<br />
reproduced by a cutoff power-law model with a photon index of<br />
$1.36^{+0.03}_{-0.04}$, being consistent with a Bremsstrahlung radiation from a<br />
thundercloud (as known as a gamma-ray glow and a thunderstorm ground<br />
enhancement). Then the gamma-ray glow was abruptly terminated with a nearby<br />
lightning discharge. The low-frequency radio monitors, installed $\sim$50 km<br />
away from the gamma-ray observation site recorded leader development of an<br />
intra/inter-cloud discharge spreading over $\sim$60 km area with a $\sim$300 ms<br />
duration. The timing of the gamma-ray termination coincided with the moment<br />
when the leader development of the intra/inter-cloud discharge passed 0.7 km<br />
horizontally away from the radiation monitors. The intra/inter-cloud discharge<br />
started $\sim$15 km away from the gamma-ray observation site. Therefore, the<br />
glow was terminated by the leader development, while it did not trigger the<br />
lightning discharge in the present case.

DOI： 10.1029/2018GL077784

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arXiv

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We report the Australia Telescope Compact Array 16 cm observation of CIZA J1358.9-4750. Recent X-ray studies imply that this galaxy cluster is composed of merging, binary clusters. Using the EW367 configuration, we found no significant diffuse radio emission in and around the cluster. An upper limit of the total radio power at 1.4 GHz is ∼1.1 × 1022 W Hz-1 in 30 square arcminutes, which is a typical size for radio relics. It is known that an empirical relation holds between the total radio power and X-ray luminosity of the host cluster. The upper limit is about one order of magnitude lower than the power expected from the relation. Very young (∼70 Myr) shocks with low Mach numbers (∼1.3), which are often seen at an early stage of merger simulations, are suggested by the previous X-ray observation. The shocks may generate cosmic-ray electrons with a steep energy spectrum, which is consistent with non-detection of bright (>1023 W Hz-1) relic in this 16 cm band observation. Based on the assumption of energy equipartition, the upper limit gives a magnetic field strength of below 0.68f(Dlos/1 Mpc)-1(γmin/200)-1 μG, where f is the cosmic-ray total energy density over the cosmic-ray electron energy density, Dlos is the depth of the shock wave along the sightline, and min is the lower cutoff Lorentz factor of the cosmic-ray electron energy spectrum.

DOI： 10.1093/pasj/psy042

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We present results from the Hitomi X-ray observation of a young composite-type supernova remnant (SNR) G21.5-0.9, whose emission is dominated by the pulsar wind nebula (PWN) contribution. The X-ray spectra in the 0.8-80 keV range obtained with the Soft X-ray Spectrometer (SXS), Soft X-ray Imager, and Hard X-ray Imager (HXI) show a significant break in the continuum as previously found with the NuSTAR observation. After taking into account all known emissions from the SNR other than the PWN itself, we find that the Hitomi spectra can be fitted with a broken power law with photon indices of 1 = 1.74 ± 0.02 and 2 = 2.14 ± 0.01 below and above the break at 7.1 ± 0.3 keV, which is significantly lower than the NuSTAR result (∼9.0 keV). The spectral break cannot be reproduced by time-dependent particle injection one-zone spectral energy distribution models, which strongly indicates that a more complex emission model is needed, as suggested by recent theoretical models. We also search for narrow emission or absorption lines with the SXS, and perform a timing analysis of PSR J1833-1034 with the HXI and the Soft Gamma-ray Detector. No significant pulsation is found from the pulsar. However, unexpectedly, narrow absorption line features are detected in the SXS data at 4.2345 keV and 9.296 keV with a significance of 3.65 s. While the origin of these features is not understood, their mere detection opens up a new field of research and was only possible with the high resolution, sensitivity, and ability to measure extended sources provided by an X-ray microcalorimeter.

DOI： 10.1093/pasj/psy027

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

In the published version of this article, (Publications of the Astronomical Society of Japan, Volume 70, Issue SP1, 2018, S22, first published online 21 December 2017, doi: 10.1093/pasj/psx132), the following error appears: The caption for figure 3 appears under figure 4 and the caption for figure 4 appears under figure 3. The publisher apologises for the error.(Figure Persenetd).

DOI： 10.1093/pasj/psy024

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  

Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background which is dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps: (1) simulation of isotope production, (2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. To demonstrate its experimental performance, the simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31°, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. The simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi4Ge3O12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.

DOI： 10.1016/j.nima.2018.02.071

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

Hitomi (ASTRO-H) was the sixth Japanese X-ray satellite that carried instruments with exquisite energy resolution of <7 eV and broad energy coverage of 0.3 to 600 keV. The Soft Gamma-ray Detector (SGD) was the Hitomi instrument that observed the highest energy band (60 to 600 keV). The SGD design achieves a low background level by combining active shields and Compton cameras where Compton kinematics is utilized to reject backgrounds coming from outside of the field of view. A compact and highly efficient Compton camera is realized using a combination of silicon and cadmium telluride semiconductor sensors with a good energy resolution. Compton kinematics also carries information for gamma-ray polarization, making the SGD an excellent polarimeter. Following several years of development, the satellite was successfully launched on February 17, 2016. After proper functionality of the SGD components were verified, the nominal observation mode was initiated on March 24, 2016. The SGD observed the Crab Nebula for approximately two hours before the spacecraft ceased to function on March 26, 2016. We present concepts of the SGD design followed by detailed description of the instrument and its performance measured on ground and in orbit.

DOI： 10.1117/1.JATIS.4.2.021411

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DOI： 10.1117/1.JATIS.4.2.021401

Web of Science

出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

DOI： 10.1117/1.JATIS.4.2.021409

Scopus

記述言語：日本語   出版者・発行元：Journal of Astronomical Telescopes, Instruments, and Systems  

The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.

DOI： 10.1117/1.JATIS.4.2.021402

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記述言語：日本語   出版者・発行元：Publications of the Astronomical Society of Japan  

Extending the earlier measurements reported in Hitomi collaboration (2016, Nature, 535, 117), we examine the atmospheric gas motions within the central 100kpc of the Perseus cluster using observations obtained with the Hitomi satellite. After correcting for the point spread function of the telescope and using optically thin emission lines, we find that the line-of-sight velocity dispersion of the hot gas is remarkably low and mostly uniform. The velocity dispersion reaches a maxima of approximately 200 km s-1 toward the central active galactic nucleus (AGN) and toward the AGN inflated northwestern "ghost" bubble. Elsewhere within the observed region, the velocity dispersion appears constant around 100 km s-1. We also detect a velocity gradient with a 100 km s-1 amplitude across the cluster core, consistent with large-scale sloshing of the core gas. If the observed gas motions are isotropic, the kinetic pressure support is less than 10% of the thermal pressure support in the cluster core. The well-resolved, optically thin emission lines have Gaussian shapes, indicating that the turbulent driving scale is likely below 100 kpc, which is consistent with the size of the AGN jet inflated bubbles. We also report the first measurement of the ion temperature in the intracluster medium, which we find to be consistent with the electron temperature. In addition, we present a new measurement of the redshift of the brightest cluster galaxy NGC 1275.

Scopus

出版者・発行元：Publications of the Astronomical Society of Japan  

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx138

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

The Hitomi Soft X-ray Spectrometer spectrum of the Perseus cluster, with ∼5 eV resolution in the 2-9 keV band, offers an unprecedented benchmark of the atomic modeling and database for hot collisional plasmas. It reveals both successes and challenges of the current atomic data and models. The latest versions of AtomDB/APEC (3.0.8), SPEX (3.03.00), and CHIANTI (8.0) all provide reasonable fits to the broad-band spectrum, and are in close agreement on best-fit temperature, emission measure, and abundances of a few elements such as Ni. For the Fe abundance, the APEC and SPEX measurements differ by 16%, which is 17 times higher than the statistical uncertainty. This is mostly attributed to the differences in adopted collisional excitation and dielectronic recombination rates of the strongest emission lines. We further investigate and compare the sensitivity of the derived physical parameters to the astrophysical source modeling and instrumental effects. The Hitomi results show that accurate atomic data and models are as important as the astrophysical modeling and instrumental calibration aspects. Substantial updates of atomic databases and targeted laboratory measurements are needed to get the current data and models ready for the data from the next Hitomi-level mission.

DOI： 10.1093/pasj/psx156

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We report on a Hitomi observation of IGRJ16318-4848, a high-mass X-ray binary system with an extremely strong absorption of NH ∼ 1024cm 2. Previous X-ray studies revealed that its spectrum is dominated by strong fluorescence lines of Fe as well as continuum emission lines. For physical and geometrical insight into the nature of the reprocessing material, we utilized the high spectroscopic resolving power of the X-ray microcalorimeter (the soft X-ray spectrometer: SXS) and the wide-band sensitivity by the soft and hard X-ray imagers (SXI and HXI) aboard Hitomi. Even though the photon counts are limited due to unintended off-axis pointing, the SXS spectrum resolves Fe Kα1 and Kα2 lines and puts strong constraints on the line centroid and line width. The line width corresponds to a velocity of 160+-37000 km s-1. This represents the most accurate, and smallest, width measurement of this line made so far from the any X-ray binary, much less than the Doppler broadening and Doppler shift expected from speeds that are characteristic of similar systems. Combined with the K-shell edge energy measured by the SXI and HXI spectra, the ionization state of Fe is estimated to be in the range of Fe I-IV. Considering the estimated ionization parameter and the distance between the X-ray source and the absorber, the density and thickness of the materials are estimated. The extraordinarily strong absorption and the absence of a Compton shoulder component have been confirmed. These characteristics suggest reprocessing materials that are distributed in a narrow solid angle or scattering, primarily by warm free electrons or neutral hydrogen. This measurement was achieved using the SXS detection of 19 photons. It provides strong motivation for follow-up observations of this and other X-ray binaries using the X-ray Astrophysics Recovery Mission and other comparable future instruments.

DOI： 10.1093/pasj/psx154

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

The present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338 ks that covered a central region of ∼7 in diameter. SXS was operated with an energy resolution of ∼5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures could be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single-temperature approximation are due to the effects of projecting the known radial temperature gradient in the cluster core along the line of sight. A comparison with the Chandra/ACIS and the XMM-Newton/RGS results, on the other hand, suggests that additional lower-temperature components are present in the intracluster medium (ICM), but not detectable with Hitomi/SXS giving its 1.8-20 keV energy band.

DOI： 10.1093/pasj/psy004

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

The Crab nebula originated from a core-collapse supernova (SN) explosion observed in 1054AD. When viewed as a supernova remnant (SNR), it has an anomalously low observed ejecta mass and kinetic energy for an Fe-core-collapse SN. Intensive searches have been made for a massive shell that solves this discrepancy, but none has been detected. An alternative idea is that SN 1054 is an electron-capture (EC) explosion with a lower explosion energy by an order of magnitude than Fe-core-collapse SNe. X-ray imaging searches were performed for the plasma emission from the shell in the Crab outskirts to set a stringent upper limit on the X-ray emitting mass. However, the extreme brightness of the source hampers access to its vicinity. We thus employed spectroscopic technique using the X-ray micro-calorimeter on board the Hitomi satellite. By exploiting its superb energy resolution, we set an upper limit for emission or absorption features from as yet undetected thermal plasma in the 2-12keV range. We also re-evaluated the existing Chandra and XMM-Newton data. By assembling these results, a new upper limit was obtained for the X-ray plasma mass of < 1 M⊙ for a wide range of assumed shell radius, size, and plasma temperature values both in and out of collisional equilibrium. To compare with the observation, we further performed hydrodynamic simulations of the Crab SNR for two SN models (Fe-core versus EC) under two SN environments (uniform interstellar medium versus progenitor wind). We found that the observed mass limit can be compatible with both SN models if the SN environment has a low density of < 0.03 cm-3 (Fe core) or < 0.1 cm-3 (EC) for the uniform density, or a progenitor wind density somewhat less than that provided by a mass loss rate of 10-5M⊙ yr-1 at 20 km s-1for the wind environment.

DOI： 10.1093/pasj/psx072

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

Thanks to its high spectral resolution (∼5 eV at 6 keV), the Soft X-ray Spectrometer (SXS) on board Hitomi enables us to measure the detailed structure of spatially resolved emission lines from highly ionized ions in galaxy clusters for the first time. In this series of papers, using the SXS we have measured the velocities of gas motions, metallicities and the multi-temperature structure of the gas in the core of the Perseus Cluster. Here, we show that when inferring physical properties from line emissivities in systems like Perseus, the resonant scattering effect should be taken into account. In the Hitomi waveband, resonant scattering mostly affects the Fe XXV Heα line (w)-the strongest line in the spectrum. The flux measured by Hitomi in this line is suppressed by a factor of ∼1.3 in the inner ∼30 kpc, compared to predictions for an optically thin plasma; the suppression decreases with the distance from the center. The w line also appears slightly broader than other lines from the same ion. The observed distortions of the w line flux, shape, and distance dependence are all consistent with the expected effect of the resonant scattering in the Perseus core. By measuring the ratio of fluxes in optically thick (w) and thin (Fe XXV forbidden, Heβ, Lyα) lines, and comparing these ratios with predictions from Monte Carlo radiative transfer simulations, the velocities of gas motions have been obtained. The results are consistent with the direct measurements of gas velocities from line broadening described elsewhere in this series, although the systematic and statistical uncertainties remain significant. Further improvements in the predictions of line emissivities in plasma models, and deeper observations with future X-ray missions offering similar or better capabilities to the Hitomi SXS, will enable resonant scattering measurements to provide powerful constraints on the amplitude and anisotropy of cluster gas motions.

DOI： 10.1093/pasj/psx127

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx083

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PubMed

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We present Hitomi observations of N 132 D, a young, X-ray bright, O-rich core-collapse supernova remnant in the Large Magellanic Cloud (LMC). Despite a very short observation of only 3.7 ks, the Soft X-ray Spectrometer (SXS) easily detects the line complexes of highly ionized S K and Fe K with 16-17 counts in each. The Fe feature is measured for the first time at high spectral resolution. Based on the plausible assumption that the Fe K emission is dominated by He-like ions, we find that the material responsible for this Fe emission is highly redshifted at ∼ 800 km s−1 compared to the local LMC interstellar medium (ISM), with a 90% credible interval of 50-1500 km s−1 if a weakly informative prior is placed on possible line broadening. This indicates (1) that the Fe emission arises from the supernova ejecta, and (2) that these ejecta are highly asymmetric, since no blueshifted component is found. The S K velocity is consistent with the local LMC ISM, and is likely from swept-up ISM material. These results are consistent with spatial mapping that shows the He-like Fe concentrated in the interior of the remnant and the S tracing the outer shell. The results also show that even with a very small number of counts, direct velocity measurements from Doppler-shifted lines detected in extended objects like supernova remnants are now possible. Thanks to the very low SXS background of ∼ 1 event per spectral resolution element per 100 ks, such results are obtainable during short pointed or slew observations with similar instruments. This highlights the power of high-spectral-resolution imaging observations, and demonstrates the new window that has been opened with Hitomi and will be greatly widened with future missions such as the X-ray Astronomy Recovery Mission (XARM) and Athena.

DOI： 10.1093/pasj/psx151

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Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

The origin of the narrow Fe-Kα fluorescence line at 6.4 keV from active galactic nuclei has long been under debate; some of the possible sites are the outer accretion disk, the broad line region, a molecular torus, or interstellar/intracluster media. In 2016 February-March, we performed the first X-ray microcalorimeter spectroscopy with the Soft X-ray Spectrometer (SXS) on board the Hitomi satellite of the Fanaroff-Riley type I radio galaxy NGC 1275 at the center of the Perseus cluster of galaxies. With the high-energy resolution of ∼5 eV at 6 keV achieved by Hitomi/SXS, we detected the Fe-Kα line with ∼5.4 σ significance. The velocity width is constrained to be 500-1600 km s−1 (FWHM for Gaussian models) at 90% confidence. The SXS also constrains the continuum level from the NGC 1275 nucleus up to ∼20 keV, giving an equivalent width of ∼20 eV for the 6.4 keV line. Because the velocity width is narrower than that of the broad Hα line of ∼2750 km s−1, we can exclude a large contribution to the line flux from the accretion disk and the broad line region. Furthermore, we performed pixel map analyses on the Hitomi/SXS data and image analyses on the Chandra archival data, and revealed that the Fe-Kα line comes from a region within ∼1.6 kpc of the NGC 1275 core, where an active galactic nucleus emission dominates, rather than that from intracluster media. Therefore, we suggest that the source of the Fe-Kα line from NGC 1275 is likely a low-covering-fraction molecular torus or a rotating molecular disk which probably extends from a parsec to hundreds of parsecs scale in the active galactic nucleus system.

DOI： 10.1093/pasj/psx147

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Monthly Notices of the Royal Astronomical Society  

We report on X-ray observations of the Dwarf Nova GK Persei performed by NuSTAR in 2015. GK Persei, behaving also as an Intermediate Polar, exhibited a Dwarf Nova outburst in 2015 March-April. The object was observed with NuSTAR during the outburst state, and again in a quiescent state wherein the 15-50 keV flux was 33 times lower. Using a multitemperature plasma emission and reflection model, the highest plasma temperature in the accretion column was measured as 19.7-1.0+1.3 keV in outburst and 36.2-3.2+3.5 keV in quiescence. The significant change of the maximum temperature is considered to reflect an accretion-induced decrease of the inner-disc radius Rin, where accreting gas is captured by the magnetosphere. Assuming this radius scales as Rin ∝ M˙ -2/7, where M˙ is themass accretion rate, we obtain Rin = 1.9-0.2+0.4 RWD and Rin = 7.4-1.2+2.1 RWD in outburst and quiescence, respectively, where RWD is the white-dwarf (WD) radius of this system. Utilizing the measured temperatures and fluxes, as well as the standard mass-radius relation ofWDs, we estimate the WD mass as MWD = 0.87 ± 0.08M⊙ including typical systematic uncertainties by 7 per cent. The surface magnetic field is also measured as B ~ 5 × 105 G. These results exemplify a new X-ray method of estimating MWD and B of WDs by using large changes in M.

DOI： 10.1093/mnras/stx2880

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPIE  

DOI： 10.1117/1.JATIS.4.1.011201

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We present a joint X-ray, optical, and weak-lensing analysis for X-ray luminous galaxy clusters selected from the MCXC (Meta-Catalog of X-Ray Detected Clusters of Galaxies) cluster catalog in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey field with S16A data. As a pilot study for a series of papers, we measure hydrostatic equilibrium (HE) masses using XMM-Newton data for four clusters in the current coverage area out of a sample of 22 MCXC clusters. We additionally analyze a non-MCXC cluster associated with one MCXC cluster. We show that HE masses for the MCXC clusters are correlated with cluster richness from the CAMIRA catalog, while that for the non-MCXC cluster deviates from the scaling relation. The mass normalization of the relationship between cluster richness and HE mass is compatible with one inferred by matching CAMIRA cluster abundance with a theoretical halo mass function. The mean gas mass fraction based on HE masses for the MCXC clusters is (fgas) = 0.125 ± 0.012 at spherical overdensity Δ = 500, which is ∼80%-90% of the cosmic mean baryon fraction, Ωb/Ωm,measured by cosmicmicrowave background experiments. We find that themean baryon fraction estimated from X-ray and HSC-SSP optical data is comparable to Ωb/Ωm. A weak-lensing shear catalog of background galaxies, combined with photometric redshifts, is currently available only for three clusters in our sample. Hydrostatic equilibrium masses roughly agree with weak-lensing masses, albeit with large uncertainty. This study demonstrates that further multi wave length study for a large sample of clusters using X-ray, HSC-SSP optical, and weak-lensing data will enable us to understand cluster physics and utilize cluster-based cosmology.

DOI： 10.1093/pasj/psx132

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

We propose a fleet of nanosatellites to perform an all-sky monitoring and timing based localisation of gamma-ray transients. The fleet of at least nine 3U cubesats shall be equipped with large and thin CsI(Tl) scintillator based soft gamma-ray detectors read out by multi-pixel photon counters. For bright short gamma-ray bursts (GRBs), by cross-correlating their light curves, the fleet shall be able to determine the time difference of the arriving GRB signal between the satellites and thus determine the source position with an accuracy of ∼ 100. This requirement demands precise time synchronization and accurate time stamping of the detected gamma-ray photons, which will be achieved by using on-board GPS receivers. Rapid follow up observations at other wavelengths require the capability for fast, nearly simultaneous downlink of data using a global inter-satellite communication network. In terms of all-sky coverage, the proposed fleet will outperform all GRB monitoring missions.

DOI： 10.1117/12.2313764

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記述言語：英語  

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.2.0_134

CiNii Research

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

A fleet of nanosatellites using precise timing synchronization provided by the Global Positioning System is a new concept for monitoring the gamma-ray sky that can achieve both all-sky coverage and good localization accuracy. We are proposing this new concept for the mission CubeSats Applied for MEasuring and LOcalising Transients (CAMELOT). The differences in photon arrival times at each satellite are to be used for source localization. Detectors with good photon statistics and the development of a localization algorithm capable of handling a large number of satellites are both essential for this mission. Large, thin CsI scintillator plates are the current candidates for the detectors because of their high light yields. It is challenging to maximize the light-collection efficiency and to understand the position dependence of such thin plates. We have found a multi-channel readout that uses the coincidence technique to be very effective in increasing the light output while keeping a similar noise level to that of a single channel readout. Based on such a detector design, we have developed a localization algorithm for this mission and have found that we can achieve a localization accuracy better than 20 arc minutes and a rate of about 10 short gamma-ray bursts per year.

DOI： 10.1117/12.2313228

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_176

CiNii Research

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.2.0_163

CiNii Research

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_422

CiNii Research

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_414

CiNii Research

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

FORCE is a 1.2 tonnes small mission dedicated for wide-band fine-imaging<br />
x-ray observation. It covers from 1 to 80 keV with a good angular resolution of<br />
$15&quot;$ half-power-diameter. It is proposed to be launched around mid-2020s and<br />
designed to reach a limiting sensitivity as good as $F_X (10-40~{\rm keV}) = 3<br />
\times 10^{-15}$~erg cm$^{-2}$ s$^{-1}$ keV$^{-1}$ within 1~Ms. This number is<br />
one order of magnitude better than current best one. With its high-sensitivity<br />
wide-band coverage, FORCE will probe the new science field of &quot;missing BHs&quot;,<br />
searching for families of black holes of which populations and evolutions are<br />
not well known. Other point-source and diffuse-source sciences are also<br />
considered. FORCE will also provide the &quot;hard x-ray coverage&quot; to forthcoming<br />
large soft x-ray observatories.

DOI： 10.1117/12.2309344

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arXiv

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of the International Astronautical Congress, IAC  

We present the results of our feasibility study for a fleet of nano-satellites to perform an all sky monitoring and timing-based localisation of gamma-ray transients. The fleet of nine satellites of the CubeSat standard equipped with scintillator based soft gamma-ray detectors will measure the time difference between the arrival of the signal at the different satellites (the time will be synchronised using GPS) and determine the location of bright gamma-ray bursts in the sky by triangulation. The satellites will downlink the data about the detected transient within minutes, enabling rapid follow-up observations at other wavelengths.

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier B.V.  

This work presents a long-term operation of two stacked CdTe double sided strip detectors that are comparable with the CdTe detectors onboard Hitomi's HXI. The goal of this test is to study the evolution of the spectroscopic performance of the detectors during a one year operation cycle which resembles the in-orbit operation cycle of Hitomi HXI. Crystal defects inside CdTe cause a degradation of the spectroscopic performance (polarization effect) of the crystal which is becoming worse during detector operation. In order to prevent crystal polarization, the detectors are reset (switch-off of the depletion voltage) once a day. Our main investigation was to study if a long-term degradation can occur as a result of incomplete depolarization during the reset. We present the hardware setup and the analytical steps that were used to investigate the detector stability during each day and over the whole testing period. For the anode signals our results show at 60 keV: a daily line drift of (−2.8±0.7) eV/ks while the long-term drift is (−1.5±1.2) eV/day. The degradation of the energy resolution is measured to be (+2.4±0.3) eV/ks FWHM and the loss of efficiency is (−0.29±0.02) %/ks.

DOI： 10.1016/j.nima.2017.11.035

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Proceedings of SPIE - The International Society for Optical Engineering  

The ASTRO-H mission was designed and developed through an international collaboration of JAXA, NASA, ESA, and the CSA. It was successfully launched on February 17, 2016, and then named Hitomi. During the in-orbit verification phase, the on-board observational instruments functioned as expected. The intricate coolant and refrigeration systems for soft X-ray spectrometer (SXS, a quantum micro-calorimeter) and soft X-ray imager (SXI, an X-ray CCD) also functioned as expected. However, on March 26, 2016, operations were prematurely terminated by a series of abnormal events and mishaps triggered by the attitude control system. These errors led to a fatal event: the loss of the solar panels on the Hitomi mission. The X-ray Astronomy Recovery Mission (or, XARM) is proposed to regain the key scientific advances anticipated by the international collaboration behind Hitomi. XARM will recover this science in the shortest time possible by focusing on one of the main science goals of Hitomi,"Resolving astrophysical problems by precise high-resolution X-ray spectroscopy".1 This decision was reached after evaluating the performance of the instruments aboard Hitomi and the mission's initial scientific results, and considering the landscape of planned international X-ray astrophysics missions in 2020's and 2030's. Hitomi opened the door to high-resolution spectroscopy in the X-ray universe. It revealed a number of discrepancies between new observational results and prior theoretical predictions. Yet, the resolution pioneered by Hitomi is also the key to answering these and other fundamental questions. The high spectral resolution realized by XARM will not offer mere refinements; rather, it will enable qualitative leaps in astrophysics and plasma physics. XARM has therefore been given a broad scientific charge: "Revealing material circulation and energy transfer in cosmic plasmas and elucidating evolution of cosmic structures and objects". To fulfill this charge, four categories of science objectives that were defined for Hitomi will also be pursued by XARM; these include (1) Structure formation of the Universe and evolution of clusters of galaxies; (2) Circulation history of baryonic matters in the Universe; (3) Transport and circulation of energy in the Universe; (4) New science with unprecedented high resolution X-ray spectroscopy. In order to achieve these scientific objectives, XARM will carry a 6 × 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces the science objectives, mission concept, and observing plan of XARM.

DOI： 10.1117/12.2309455

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CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/pasj/psx095

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature  

Lightning and thunderclouds are natural particle accelerators. Avalanches of relativistic runaway electrons, which develop in electric fields within thunderclouds, emit bremsstrahlung Î 3-rays. These Î 3-rays have been detected by ground-based observatories, by airborne detectors and as terrestrial Î 3-ray flashes from space. The energy of the Î 3-rays is sufficiently high that they can trigger atmospheric photonuclear reactions that produce neutrons and eventually positrons via β + decay of the unstable radioactive isotopes, most notably 13 N, which is generated via 14 N + Î 3 â †' 13 N + n, where Î 3 denotes a photon and n a neutron. However, this reaction has hitherto not been observed conclusively, despite increasing observational evidence of neutrons and positrons that are presumably derived from such reactions. Here we report ground-based observations of neutron and positron signals after lightning. During a thunderstorm on 6 February 2017 in Japan, a Î 3-ray flash with a duration of less than one millisecond was detected at our monitoring sites 0.5-1.7 kilometres away from the lightning. The subsequent Î 3-ray afterglow subsided quickly, with an exponential decay constant of 40-60 milliseconds, and was followed by prolonged line emission at about 0.511 megaelectronvolts, which lasted for a minute. The observed decay timescale and spectral cutoff at about 10 megaelectronvolts of the Î 3-ray afterglow are well explained by de-excitation Î 3-rays from nuclei excited by neutron capture. The centre energy of the prolonged line emission corresponds to electron-positron annihilation, providing conclusive evidence of positrons being produced after the lightning.

DOI： 10.1038/nature24630

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature  

The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae. Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode. Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun, suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, high-resolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near- A nd sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment.

DOI： 10.1038/nature24301

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PubMed

記述言語：英語   出版者・発行元：Publications of the Astronomical Society of Japan  

We will review results for gamma-ray bursts (GRBs) and soft gamma repeaters (SGRs), obtained from the Suzaku Wide-band All-sky Monitor (WAM) which operated for about 10 years from 2005 to 2015. The WAM is a BGO (bismuth germanate: Bi 4 Ge 3 O 12) lateral shield for the Hard X-ray Detector (HXD), used mainly for rejecting its detector background, but it also works as an all-sky monitor for soft gamma-ray transients in the 50-5000 keV range thanks to its large effective area (∼600 cm 2 at 1 MeV for one detector) and wide field of view (about half of the entire sky). The WAM actually detected more than 1400 GRBs and 300 bursts from SGRs, and this detection number is comparable to that of other GRB-specific instruments. Based on the 10 years of operation, we describe timing and spectral performance for short GRBs, weak GRBs with high redshifts, and time-resolved pulses with good statistics.

DOI： 10.1093/pasj/psx026

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

The recurrent soft X-ray transient Aquila X-1 was observed with Suzaku for a gross duration of 79.9 ks, on 2011 October 21 when the object was in a rising phase of an outburst. During the observation, the source exhibited a clear spectral transition from the hard state to the soft state, on a time scale of ∼30 ks. Across the transition, the 0.8-10 keV X-Ray Imaging Spectrometer count rate increased by a factor ∼3, that of Hard X-ray Detector PIN (HXD-PIN) in 15-60 keV decreased by a similar factor, and the unabsorbed 0.1-100 keV luminosity increased from 3.5 × 1037 erg s-1 to 5.1 × 1037 erg s-1. The broadband spectral shape changed continuously, from a power-law-like one with a high-energy cut-off to a more convex one. Throughout the transition, the 0.8-60 keV spectra were successfully described with a model consisting of a multi-color blackbody and a Comptonized blackbody, which are considered to arise from a standard accretion disk and a closer vicinity of the neutron star, respectively. All the model parameters were confirmed to change continuously, from those typical in the hard state to those typical of the soft state. More specifically, the inner disk radius decreased from 31 km to 18 km, the effects of Comptonization on the blackbody photons weakened, and the electron temperature of Comptonization decreased from 10 keV to 3 keV. The derived parameters imply that the Comptonizing corona shrinks towards the final soft state, and/or the radial infall velocity of the corona decreases. These results reinforce the view that the soft and hard states of Aql X-1 (and of similar objects) are described by the same "disk plus Comptonized blackbody" model, but with considerably different parameters.

DOI： 10.1093/pasj/psw126

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

We present the results of deep 140 ks Suzaku X-ray observations of the north-east (NE) radio relic of the merging galaxy cluster Abell 2255. The temperature structure of Abell 2255 is measured out to 0.9 times the virial radius (1.9 Mpc) in the NE direction for the first time. The Suzaku temperature map of the central region suggests a complex temperature distribution, which agrees with previous work. Additionally, on a larger-scale, we confirm that the temperature drops from 6 keV around the cluster center to 3 keV at the outskirts, with two discontinuities at r similar to 5' (450 kpc) and similar to 12' (1100 kpc) from the cluster center. Their locations coincide with surface brightness discontinuities marginally detected in the XMM-Newton image, which indicates the presence of shock structures. From the temperature drop, we estimate the Mach numbers to be M-inner similar to 1.2 and, M-outer similar to 1:4. The first structure is most likely related to the large cluster core region (similar to 350-430 kpc), and its Mach number is consistent with the XMM-Newton observation (M similar to 1.24: Sakelliou & Ponman 2006, MNRAS, 367, 1409). Our detection of the second temperature jump, based on the Suzaku key project observation, shows the presence of a shock structure across the NE radio relic. This indicates a connection between the shock structure and the relativistic electrons that generate radio emission. Across the NE radio relic, however, we find a significantly lower temperature ratio (T-1/T-2 similar to 1.44 +/- 0.16 corresponds to M-X (ray) similar to 1.4) than the value expected from radio wavelengths, based on the standard diffusive shock acceleration mechanism (T-1/T-2 &gt; 3.2 or M-Radio &gt; 2.8). This may suggest that under some conditions, in particular the NE relic of A2255 case, the simple diffusive shock acceleration mechanism is unlikely to be valid, and therefore, more a sophisticated mechanism is required.

DOI： 10.1051/0004-6361/201628400

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Astrophysical Journal Letters  

High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E ≈ 3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S xvi (E ≃ 3.44 keV rest-frame) - a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

DOI： 10.3847/2041-8213/aa61fa

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Publications of the Astronomical Society of Japan  

We present the Chandra and Suzaku observations of 1RXS J170047.8-314442, located towards the Galactic bulge, to reveal a wide-band (0.3-10keV) X-ray morphology and spectrum of this source. With the Chandra observation, no point source was found at the position of 1RXS J170047.8-314442. Instead, we revealed the presence of diffuse X-ray emission, via the wide-band X-ray image obtained from the Suzaku XIS. Although the X-rayemission had a nearly circularshape with a spatial extent of ∼3.5, the surface brightness profile was not axisymmetric; a bright spot-like emission was found at ∼ 1' away in the northwestern direction from the center. The radial profile of the surface brightness, except for this spot-like emission, was reproduced with a single β-model; β and the core radius were found to be 1.02 and 1.51, respectively. The X-ray spectrum of the diffuse emission showed an emission line at ∼6keV, indicating an origin of a thermal plasma. The spectrum was well explained with an absorbed, optically-thin thermal plasma model with a temperature of 6.2 keVand a redshift parameter of z= 0.14 ±0.01. Hence, the X-ray emission was considered to arise from the hot gas associated with a cluster of galaxies. Our spectroscopic result confirmed the optical identification of 1RXS J170047.8-314442 by Kocevski et al. (2007, ApJ, 662, 224): CIZAJ1700.8-3144, a member of the cluster catalogue in the Zone of Avoidance. The estimated bolometric X-ray luminosity of 5.9 × 1044 erg s-1 was among the lowest with this temperature, suggesting that this cluster is far from relaxed.

DOI： 10.1093/pasj/psw106

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Observations of the ultra-luminous X-ray source (ULX) Holmberg IX X-1 were carried out with Suzaku twice, once on 2012 April 13 and then on 2012 October 24, with exposures of 180 ks and 217 ks, respectively. The source showed a hard power-law shaped spectrum with a mild cutoff at similar to 8 keV, which is typical of ULXs when they are relatively dim. On both occasions, the 0.6-11 keV spectrum was explained successfully in terms of a cool (similar to 0.2 keV) multi-color disk blackbody emission model and thermal Comptonization emission produced by an electron cloud with a relatively low temperature and high optical depth, assuming that a large fraction of the disk-blackbody photons are Comptonized whereas the rest are observed directly. The 0.5-10 keV luminosity was 1.2 x 10(40) erg s(-1) in April, and similar to 14% higher in October. This brightening was accompanied by spectral softening in &gt;= 2 keV, with little change in the &lt;= 2 keV spectral shape. This behavior can be understood if the accretion disk remains unchanged while the electron cloud covers a variable fraction of the disk. The absorbing column density was consistent with the galactic line-of sight value, and did not vary by more than 1.6 x 10(21) cm(-2). Together with the featureless spectra, these properties may not be reconciled easily with the supercritical accretion scenario of this source.

DOI： 10.1093/pasj/psw108

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.72.2.0_414

CiNii Research

記述言語：日本語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Journal of Physics: Conference Series  

DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe. DECIGO will consists of three drag-free spacecraft arranged in an equilateral triangle with 1000 km arm lengths whose relative displacements are measured by a differential Fabry-Perot interferometer, and four units of triangular Fabry-Perot interferometers are arranged on heliocentric orbit around the sun. DECIGO is vary ambitious mission, we plan to launch DECIGO in era of 2030s after precursor satellite mission, B-DECIGO. B-DECIGO is essentially smaller version of DECIGO: B-DECIGO consists of three spacecraft arranged in an triangle with 100 km arm lengths orbiting 2000 km above the surface of the earth. It is hoped that the launch date will be late 2020s for the present..

DOI： 10.1088/1742-6596/840/1/012010

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

We report on NuSTAR observations of the intermediate polar GK Persei which also behaves as a dwarf nova. It exhibited a dwarf nova outburst in 2015 March April. The object was observed in 3-79 keV X-rays with NuSTAR, once at the outburst peak, and again in 2015 September during quiescence. The 5-50 keV flux during the outburst was 26 times higher than that during the quiescence. With a multi-temperature emission model and a reflection model, we derived the post-shock temperature as 19.2 +/- 0.7 keV in the outburst, and 38.5(-3.6)(+4.1) keV in the quiescence. This temperature difference is considered to reflect changes in the radius at which the accreting matter, forming an accretion disk, is captured by the magnetosphere of the white dwarf (WD). Assuming that this radius scales as the power of -2/7 of the mass accretion rate, and utilizing the two temperature measurements, as well as the standard mass-radius relation of WDs, we determined the WD mass in GK Persei as 0.90 +/- 0.06 solar masses. The magnetic field is estimated as 4 x 10(5) G.

Web of Science

掲載種別：研究論文（国際会議プロシーディングス）  

The Focusing On Relativistic universe and Cosmic Evolution (FORCE) mission is proposed as a future Japan-lead X-ray observatory to be launched in the mid 2020s. FORCE is a successor of Hitomi, focusing on the braodband X-ray imaging spectroscopy in 1–80 keV with a significantly higher angular resolution of < 15′′ in half-power diameter. The sensitivity above 10 keV will be 10 times higher than that of any previous hard X-ray missions with simultaneous soft X-ray coverage. The satellite is planned to be launched by the Epsilon vehicle by ISAS/JAXA. In the current design concept, FORCE is equipped with three identical pairs of supermirrors and wideband X-ray detectors. The focal length of the mirrors is 10 m. The silicon mirror with multi-layer coating is our primary choice of optics to achieve a good angular resolution for the wide energy band while maintaining a light weight. The detector is a hybrid of a SOI-CMOS silicon-pixel detector and a CdTe detector responsible for the softer and harder energy bands, respectively. It is basically a descendant of the hard X-ray imager onboard Hitomi with its soft-band detector replaced with the SOI-CMOS. The primary scientific objective of the FORCE mission is to trace the cosmic formation history by searching for “missing black holes” in the entire range of the mass spectrum of BHs: “buried” supermassive black holes (SMBHs) (> 104 M), intermediate-mass black holes (102–104 M), and “orphan” stellar-mass black holes (< 102 M). Also, investigation of the nature of relativistic particles at various astrophysical shocks is in our scope, with high-angular-resolution X-ray observations with the broadband coverage. FORCE will open a new era in these fields.

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記述言語：日本語   掲載種別：機関テクニカルレポート，技術報告書，プレプリント等   出版者・発行元：一般社団法人 日本物理学会  

We present the results from the Hitomi Soft Gamma-ray Detector (SGD)<br />
observation of the Crab nebula. The main part of SGD is a Compton camera, which<br />
in addition to being a spectrometer, is capable of measuring polarization of<br />
gamma-ray photons. The Crab nebula is one of the brightest X-ray / gamma-ray<br />
sources on the sky, and, the only source from which polarized X-ray photons<br />
have been detected. SGD observed the Crab nebula during the initial test<br />
observation phase of Hitomi. We performed the data analysis of the SGD<br />
observation, the SGD background estimation and the SGD Monte Carlo simulations,<br />
and, successfully detected polarized gamma-ray emission from the Crab nebula<br />
with only about 5 ks exposure time. The obtained polarization fraction of the<br />
phase-integrated Crab emission (sum of pulsar and nebula emissions) is (22.1<br />
$\pm$ 10.6)% and, the polarization angle is 110.7$^o$ + 13.2 / $-$13.0$^o$ in<br />
the energy range of 60--160 keV (The errors correspond to the 1 sigma<br />
deviation). The confidence level of the polarization detection was 99.3%. The<br />
polarization angle measured by SGD is about one sigma deviation with the<br />
projected spin axis of the pulsar, 124.0$^o$ $\pm$0.1$^o$.

DOI： 10.11316/jpsgaiyo.73.1.0_492

arXiv

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記述言語：英語   掲載種別：機関テクニカルレポート，技術報告書，プレプリント等  

We present an X-ray study of the GeV gamma-ray supernova remnant (SNR) HB 21<br />
with Suzaku. HB 21 is interacting with molecular clouds and the faintest in the<br />
GeV band among known GeV SNRs. We discovered strong radiative recombination<br />
continua of Si and S from the center of the remnant, which provide the direct<br />
evidence of a recombining plasma (RP). The total emission can be explained with<br />
the RP and ionizing plasma components. The electron temperature and<br />
recombination timescale of the RP component were estimated as 0.17 (0.15-0.18)<br />
keV and 3.2 (2.0-4.8) $\times$ 10$^{11}$ s cm$^{-3}$, respectively. The<br />
estimated age of the RP (RP age; $\sim$ 170 kyr) is the longest among known<br />
recombining GeV SNRs, because of very low density of electrons ($\sim$ 0.05<br />
cm$^{-3}$). We have examined dependencies of GeV spectral indices on each of RP<br />
ages and SNR diameters for nine recombining GeV SNRs. Both showed possible<br />
positive correlations, indicating that both the parameters can be good<br />
indicators of properties of accelerated protons, for instance, degree of escape<br />
from the SNR shocks. A possible scenario for a process of proton escape is<br />
introduced; interaction with molecular clouds makes weaker magnetic turbulence<br />
and cosmic-ray protons escape, simultaneously cooling down the thermal<br />
electrons and generate an RP.

DOI： 10.1093/pasj/psy069

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arXiv

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_414

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_176

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_422

CiNii Research

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_423

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.72.2.0_412

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.72.2.0_413

J-GLOBAL

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>NGHXTあらため、FORCE衛星は1-80 keVの広帯域X線を高感度で撮像分光し、まだ見ぬ隠されたブラックホールや超新星残骸のフィラメントでの粒子加速の探査を目指している。2016年に変更した計画の内容、検出器および望遠鏡の開発状況、およびサイエンス検討の進捗を報告する。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_508

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>我々は雷雲内の粒子加速機構の解明を目指し，新潟県柏崎刈羽原発内で雷雲由来ガンマ線の測定を継続している。2014–15年冬には約100秒間に10万カウント前後という高統計のガンマ線増大現象が複数観測され，地上に届くガンマ線放射の広がりの大きさや形状が判明した。本講演ではモンテカルロシミュレーションを用いて，電場加速された電子が地上にもたらす制動放射ガンマ線の分布をモデル化し，実データと比較することで，加速現場の高度や加速方向の広がりを推定する。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_500

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>我々は10年にわたり新潟県柏崎刈羽原発内に検出器を設置して雷雲由来のガンマ線を測定し，雷雲内の粒子加速機構の解明を目指してきた。本年度、我々はコリメーターを用いることで方向に対し感度を持つ検出器を新たに設置した。本講演ではその運用成果について報告する。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_501

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>我々はこれまで10年にわたり新潟県柏崎刈羽原発内に検出器を設置して雷雲由来のガンマ線を観測し、放射機構の解明を目指してきた。2014,2015年に観測された事象の空間分布を調べたところ、強度変動の主原因が雷雲の移動で、放射が到達した領域が1 kmスケールの楕円であることが確定し、2分程度にわたり放射が持続したことも判明した。これに基づき、これまで観測された全事象について系統的なスペクトル・カウント数の時系列解析を行った。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_499

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記述言語：日本語   出版者・発行元：宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)  

第17回宇宙科学シンポジウム (2017年1月5日-6日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)相模原キャンパス), 相模原市, 神奈川県著者人数: 56名ほか (JAXA staff: Ishida, Manabu ; Kokubun, Motohide ; Watanabe, Shin ; Iizuka, Ryo ; Ohta, Masayuki ; Sato, Rie ; Takahashi, Tadayuki ; Hagino, Koichi ; Harayama, Atsushi ; Maeda, Yoshitomo)資料番号: SA6000060046レポート番号: P-004

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>雷雲ガンマ線の観測プロジェクトは2015年度より多地点によるマッピング観測を目指し、石川県でも展開を進めている。初年度の運用実績や成果を元にしてADC/FPGAによる読み出し系の改良を中心に開発を行い、小型ガンマ線検出器の台数を増やしつつある。これらの検出器は金沢市内、小松市内、及び柏崎刈羽原発内に設置し、マッピング観測を本格的に開始している。本講演では小型検出器の開発状況、および今年度の運用状況・成果について報告する。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_503

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>雷雲内の強電場で加速された電子からの制動放射ガンマ線を観測するプロジェクトは、2006年に柏崎で観測を開始して以来10年になり、観測事例も蓄積され、基本的な描像は確立しつつある。しかし、電子の加速領域の大きさや継続時間はこれまでの定点観測では把握が難しかったため、石川県内の複数の学校の屋上に、小型で低消費電力の放射線検出器を設置し、マッピング観測を新たに開始した。多地点観測への新展開プロジェクトの狙いと現状を報告する。</p>

DOI： 10.11316/jpsgaiyo.72.1.0_502

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