S Watanabe

Japan Aerospace Exploration Agency, Chōfu, Tōkyō, Japan

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Publications (331)650.91 Total impact

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    ABSTRACT: Solar flares accelerate particles up to high energies (MeV and GeV scales for electrons and ions, respectively) through efficient acceleration processes that are not currently understood. Hard X-rays (HXRs) are the most direct diagnostic of flare-accelerated electrons. However, past and current solar HXR observers lack the necessary sensitivity and imaging dynamic range to make detailed studies of faint HXR sources in the solar corona (where particle acceleration is thought to occur); these limitations are mainly due to the indirect Fourier imaging techniques used by these observers. With greater sensitivity and dynamic range, electron acceleration sites could be systematically studied in detail. Both these capabilities can be advanced by the use of direct focusing optics. The recently own Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload demonstrates the unique diagnostic power of focusing optics for observations of solar HXRs. FOXSI features grazing-incidence replicated nickel optics with 5 arcsecond resolution and fine-pitch silicon strip detectors with a 7.7 arcsecond strip pitch. FOXSI flew successfully on 2012 November 2, producing images and spectra of a microflare and performing a search for non-thermal emission (4{15 keV) from nanoflares occurring outside active regions in the quiet Sun. A future spacecraft version of FOXSI, featuring similar optics and detectors, could make detailed observations of HXRs from flare-accelerated electrons, identifying and characterizing particle acceleration sites and mapping out paths of energetic electrons as they leave these sites and propagate throughout the solar corona. This paper will describe the FOXSI instrument and present images from the first flight.
    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 09/2013
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    ABSTRACT: Understanding electron acceleration in solar flares requires X-ray studies with greater sensitivity and dynamic range than are available with current solar hard X-ray observers (i.e. the RHESSI spacecraft). RHESSI employs an indirect Fourier imaging method that is intrinsically limited in dynamic range and therefore can rarely image faint coronal flare sources in the presence of bright footpoints. With greater sensitivity and dynamic range, electron acceleration sites in the corona could be studied in great detail. Both these capabilities can be advanced by the use of direct focusing optics. The recently flown Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload demonstrates the feasibility and usefulness of hard X-ray focusing optics for observations of solar hard X-rays. FOXSI features grazing-incidence replicated nickel optics made by the NASA Marshall Space Flight Center and fine-pitch silicon strip detectors developed by the Astro-H team at JAXA/ISAS. FOXSI flew successfully on November 2, 2012, producing images and spectra of a microflare and performing a search for nonthermal emission (4-15 keV) from nanoflares in the quiet Sun. Nanoflares are a candidate for providing the required energy to heat the solar corona to its high temperature of a few million degrees. A future satellite version of FOXSI, featuring similar optics and detectors, could make detailed observations of hard X-rays from flare-accelerated electrons, identifying and characterizing particle acceleration sites and mapping out paths of energetic electrons as they leave these sites and propagate throughout the solar corona.Abstract (2,250 Maximum Characters): Understanding electron acceleration in solar flares requires X-ray studies with greater sensitivity and dynamic range than are available with current solar hard X-ray observers (i.e. the RHESSI spacecraft). RHESSI employs an indirect Fourier imaging method that is intrinsically limited in dynamic range and therefore can rarely image faint coronal flare sources in the presence of bright footpoints. With greater sensitivity and dynamic range, electron acceleration sites in the corona could be studied in great detail. Both these capabilities can be advanced by the use of direct focusing optics. The recently flown Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload demonstrates the feasibility and usefulness of hard X-ray focusing optics for observations of solar hard X-rays. FOXSI features grazing-incidence replicated nickel optics made by the NASA Marshall Space Flight Center and fine-pitch silicon strip detectors developed by the Astro-H team at JAXA/ISAS. FOXSI flew successfully on November 2, 2012, producing images and spectra of a microflare and performing a search for nonthermal emission (4-15 keV) from nanoflares in the quiet Sun. Nanoflares are a candidate for providing the required energy to heat the solar corona to its high temperature of a few million degrees. A future satellite version of FOXSI, featuring similar optics and detectors, could make detailed observations of hard X-rays from flare-accelerated electrons, identifying and characterizing particle acceleration sites and mapping out paths of energetic electrons as they leave these sites and propagate throughout the solar corona.
    AAS/Solar Physics Division Meeting; 07/2013
  • AAS/Solar Physics Division Meeting; 07/2013
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    ABSTRACT: We evaluate the exposure during nadir observations with JEM-EUSO, the Extreme Universe Space Observatory, on-board the Japanese Experiment Module of the International Space Station. Designed as a mission to explore the extreme energy Universe from space, JEM-EUSO will monitor the Earth's nighttime atmosphere to record the ultraviolet light from tracks generated by extensive air showers initiated by ultra-high energy cosmic rays. In the present work, we discuss the particularities of space-based observation and we compute the annual exposure in nadir observation. The results are based on studies of the expected trigger aperture and observational duty cycle, as well as, on the investigations of the effects of clouds and different types of background light. We show that the annual exposure is about one order of magnitude higher than those of the presently operating ground-based observatories.
    05/2013;
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    ABSTRACT: Astro-H is the sixth Japanese X-ray space observatory which will be launched in 2014. Two of onboard instruments of Astro-H, Hard X-ray Imager and Soft Gamma-ray Detector are surrounded by many number of large Bismuth Germanate (Bi4Ge3O12; BGO) scintillators. Optimum readout system of scintillation lights from these BGOs are essential to reduce the background signals and achieve high performance for main detectors because most of gamma-rays from out of field-of-view of main detectors or radio-isotopes produced inside them due to activation can be eliminated by anti-coincidence technique using BGO signals. We apply Avalanche Photo Diode (APD) for light sensor of these BGO detectors since their compactness and high quantum efficiency make it easy to design such large number of BGO detector system. For signal processing from APDs, digital filter and other trigger logics on the Field-Programmable Gate Array (FPGA) is used instead of discrete analog circuits due to limitation of circuit implementation area on spacecraft. For efficient observations, we have to achieve as low threshold of anti-coincidence signal as possible by utilizing the digital filtering. In addition, such anti-coincident signals should be sent to the main detector within 5μs to make it in time to veto the A–D conversion. Considering this requirement and constraint from logic size of FPGA, we adopt two types of filter, 8 delay taps filter with only 2 bit precision coefficient and 16 delay taps filter with 8 bit precision coefficient. The data after former simple filter provides anti-coincidence signal quickly in orbit, and the latter filter is used for detail analysis after the data is down-linked.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2013; 699:112–115. · 1.14 Impact Factor
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    ABSTRACT: The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultra-dense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (<1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m^2 peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of <5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO's to year-long transient outbursts. In this paper we report the current status of the project.
    Experimental Astronomy 09/2012; 34(2). · 2.97 Impact Factor
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    ABSTRACT: Contributions of the JEM-EUSO Collaboration to the 32nd International Cosmic Ray Conference, Beijing, August, 2011.
    04/2012;
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    ABSTRACT: We are developing an integrated simulation framework based on Geant4 to estimate in-orbit performance of instruments onboard ASTRO-H, the international X-ray observatory to be launched in 2014. One of the most important purposes of our simulation is to estimate radiation background of the Hard X-ray Imager (HXI) and the Soft Gamma-ray Detector (SGD), both of which are composed of CdTe and silicon. We developed a new code based on Geant4 to handle the generation and the decay of radioactive nuclei and to estimate the activation of CdTe detector. In addition, to verify simulation results, we performed beam irradiation experiments at NIRS IDMAC using 150 MeV protons, which is typical energy of protons reaching to the CdTe detectors placed in the shielding materials, and measured the activation background spectra for several months. Our simulation results show good agreements with the experimental data.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: Dust containing radioactive materials dispersed following the Fukushima nuclear power plant accident in March 2011. Gamma-rays are emitted in the process when unstable nuclei in the materials decay. Based on the technology of Si/CdTe Compton Camera, we have manufactured a quick prototype model for the use in the field. The camera, now called a "Ultra-Wide-Angle Compton Camera" was successfully applied to visualize the distribution of radio-active substances in the Fukushima area.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: Hard X-ray Detector (HXD) onboard Suzaku, the Japanese 5th X-ray observatory, consists of 64 PIN photo diodes with 2 mm thickness (10-70 keV) and 16 phoswich detectors using 5 mm-thick GSO scintillators and BGO active collimators (40-600 keV), and these are surrounded by 20 units of BGO Active shields. All the detector units have been working well with no significant troubles in four and a half years since the launch on July 2005, and given many important scientific results. In this paper, we report the recent status of on-orbit calibrations for PIN/GSO detectors. For the PIN, analog/digital threshold levels of both in-orbit and on-ground are raised up to avoid the increasing noise events due to in-orbit radiation damage. For the GSO, the accuracy of the energy scale and modeling of gain variations are improved, and newly calibrated data set including background files and response matrices are released on April 2010.
    Proc SPIE 07/2010;
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    ABSTRACT: The Soft Gamma-ray Detector onboard the ASTRO-H satellite, scheduled for launch in 2014, is a Si/CdTe Compton telescope surrounded by a thick BGO active shield. The SGD covers the energy range from 40 to 600 keV and studies non-thermal phenomena in the universe with high sensitivity. For the success of the SGD mission, careful examination of the expected performance, particularly the instrumental background in orbit, and optimization of the detector configuration are essential. We are developing a Geant4-based Monte Carlo simulation framework on the ANL++ platform, employing the MGGPOD software suite to predict the radioactivation in orbit. A detailed validation of the simulator through the comparison with literature and the beam test data is summarized. Our system will be integrated into the ASTRO-H simulation framework.
    Proc SPIE 07/2010;
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    ABSTRACT: Soft Gamma-ray Detector (SGD:40-600 keV) will be mounted on the 6th Japanese X-ray observatory ASTROH to be launched in 2014. The main part of the SGD is a Compton camera with a narrow field of view and surrounded by BGO active shields (SGD-BGO). Via this combination, the SGD can achieve sensitivity more than ten times superior to the Suzaku/HXD. The BGO active shield will also function as a gamma-ray burst monitor as proven by the wide-band all-sky monitor (WAM) of the Suzaku/HXD. Avalanche Photodiodes (APDs) are used to read out scintillation lights from the BGO. The size of the former also means we need to focus on collecting light from large, complex-shaped BGO blocks. The significant leakage current of the APD means a lower temperature is preferred to minimize the noise while a higher temperature is preferred to simplify the cooling system. To optimize the BGO shape and the operating temperature, we tested the performance of the BGO readout system with various BGO shapes under different operating temperatures. We also apply waveform sampling by flash-ADC and digital filter instead of a conventional analog filter and ADC scheme to reduce the space and power of the circuit with increased flexibilities. As an active shield, we need to achieve a threshold level of 50-100 keV. Here, we report on the studies of threshold energy of active shield under various conditions and signal processings.
    Proc SPIE 07/2010;
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    ABSTRACT: A semiconductor Compton camera with wide-band imaging capability and high energy resolution is expected to provide new in-vivo data that enables tracking of multiple RI-labeled molecular probes. In our previous works, we have constructed prototype Compton cameras composed of Si and CdTe semiconductor detectors, and demonstrated wide-band imaging of 60-662 keV gamma-rays with a spatial resolution on the order of millimeters for a 2-D target. The feasibility of 3-D imaging is studied by Monte Carlo simulations that were validated in our previous work, in order to apply this camera to in-vivo molecular imaging and clinical use.
    01/2010;
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    ABSTRACT: The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA sounding rocket mission which will study particle acceleration and coronal heating on the Sun through unprecedented high-resolution imaging in the hard X-ray energy band (5-15 keV). Energy release occurring in the quiet region of the Sun may potentially play an important role in the coronal heating mechanism. With a combination of high-resolution focusing X-ray optics and fine-pitch imaging sensors, FOXSI will achieve superior sensitivity; two orders of magnitude better than that of the RHESSI satellite. FOXSI requires the spectral capability down to 5 keV, which requires a development of a new ASIC and detector with a better energy resolution. We plan to use a Double-sided Si Strip Detector (DSSD) with a low-noise front-end ASIC as the FOXSI focal plane detector, which will fulfill the scientific requirements on the spatial resolution, energy resolution, lower threshold energy and time resolution. We have designed and fabricated a DSSD with a thickness of 500 ¿m and a dimension of 9.6 mm×9.6 mm, containing 128 strips separated by a pitch of 75 ¿m, which corresponds to 8 arcsec at the focal length of 2 m. The DSSD was successfully operated in a laboratory experiment. Under a temperature of -20°C and a bias voltage of 250 V, we obtained spectra from both sides of the electrodes. The energy resolution was measured to be 980 eV and 2.4 keV for the p-side and n-side at 14 keV gamma-ray, sufficient for the FOXSI mission requirement.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
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    ABSTRACT: SS433, located at the center of the supernova remnant W50, is a close proximity binary system consisting of a compact star and a normal star. Jets of material are directed outwards from the vicinity of the compact star symmetrically to the east and west. Non-thermal hard X-ray emission is detected from lobes lying on both sides. Shock accelerated electrons are expected to generate sub-TeV gamma rays through the inverse-Compton process in the lobes. Observations of the western X-ray lobe region of SS433/W50 system have been performed to detect sub-TeV gamma-rays using the 10m CANGAROO-II telescope in August and September, 2001, and July and September, 2002. The total observation times are 85.2 hours for ON source, and 80.8 hours for OFF source data. No significant excess of sub-TeV gamma rays has been found at 3 regions of the western X-ray lobe of SS433/W50 system. We have derived 99% confidence level upper limits to the fluxes of gamma rays and have set constraints on the strengths of the magnetic fields assuming the synchrotron/inverse-Compton model for the wide energy range of photon spectrum from radio to TeV. The derived lower limits are 4.3 microgauss for the center of the brightest X-ray emission region and 6.3 microgauss for the far end from SS433 in the western X-ray lobe. In addition, we suggest that the spot-like X-ray emission may provide a major contribution to the hardest X-ray spectrum in the lobe. Comment: 7 pages, 8 figures, to be published in Astroparticle Physics
    09/2009;
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    ABSTRACT: Because accretion and merger shocks in clusters of galaxies may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmic-rays. A prediction was presented for gamma-ray emission from a cluster of galaxies at a detectable level with the current generation of imaging atmospheric Cherenkov telescopes. The gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background (CMB) photons by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster. We observed two clusters of galaxies, Abell 3667 and Abell 4038, searching for very-high-energy gamma-ray emission with the CANGAROO-III atmospheric Cherenkov telescope system in 2006. The analysis showed no significant excess around these clusters, yielding upper limits on the gamma-ray emission. From a comparison of the upper limit for the north-west radio relic region of Abell 3667 with a model prediction, we derive a lower limit for the magnetic field of the region of ~0.1 micro G. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions using a model of gamma-ray emission from neutral pions produced in hadronic collisions of cosmic-ray protons with the intra-cluster medium (ICM). The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxy. Comment: 7 pages, 6 figures, Accepted in ApJ
    The Astrophysical Journal 08/2009; · 6.73 Impact Factor
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    ABSTRACT: Observation by the CANGAROO-III stereoscopic system of the Imaging Cherenkov Telescope has detected extended emission of TeV gamma rays in the vicinity of the pulsar PSR B1706$-$44. The strength of the signal observed as gamma-ray-like events varies when we apply different ways of emulating background events. The reason for such uncertainties is argued in relevance to gamma-rays embedded in the "off-source data", that is, unknown sources and diffuse emission in the Galactic plane, namely, the existence of a complex structure of TeV gamma-ray emission around PSR B1706$-$44. Comment: 10 pages, 13 figures, to be published in ApJ
    The Astrophysical Journal 08/2009; · 6.73 Impact Factor
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    ABSTRACT: A semiconductor Compton camera that combines silicon (Si) and cadmium telluride (CdTe) detectors was developed, and its imaging capability was examined with various kinds of gamma-ray targets such as a point source, arranged point sources and an extended source. The camera consists of one double-sided Si strip detector and four layers of CdTe pad detectors, and was designed to minimize the distance between a scatterer and the target. This is because the spatial resolution with Compton imaging improves as the target approaches the scatterer. This new camera realizes a minimum distance of 25 mm. By placing the target at a distance of 30 mm from the detector, resolving power better than 3 mm was demonstrated experimentally for a 364 keV (<sup>131</sup>I) gamma-ray. Positional determination with accuracy of 1 mm was also demonstrated. As a deconvolution method, we selected the iteration algorithm (called List-Mode Expectation-Maximizing Maximum Likelihood), and applied it to several kinds of experimental data. The Compton back projection images of the arranged point sources and an extended object were successfully deconvolved.
    IEEE Transactions on Nuclear Science 07/2009; · 1.22 Impact Factor
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    ABSTRACT: Copper-64 was produced by the 64Ni(p, n)64Cu reaction using enriched 64NiO target. We investigated and compared the production yield of 64Cu for proton beams of various energies by using a thick target. Enriched 64Ni was recovered with high yield by simple procedures. Imaging studies using positron emission tomography (PET) and positron emitting tracer imaging system (PETIS) were performed. We obtained clear images in PET and PETIS studies. The results of this study indicate that 64Cu can be utilized as a biomedical tracer for the molecular imaging both in animals and plants.
    Journal of Radioanalytical and Nuclear Chemistry 01/2009; 280(1). · 1.47 Impact Factor

Publication Stats

2k Citations
650.91 Total Impact Points

Institutions

  • 2004–2013
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tōkyō, Japan
  • 2003–2009
    • Kyoto University
      • Department of Physics II
      Kioto, Kyōto, Japan
    • Shinshu University
      • Department of Chemistry
      Shonai, Nagano, Japan
    • The University of Tokyo
      • Department of Physics
      Tokyo, Tokyo-to, Japan
  • 2006–2008
    • University of Occupational and Environmental Health
      • School of Medicine
      Kitakyūshū, Fukuoka-ken, Japan
    • Tohoku University
      • Institute for Materials Research
      Sendai, Kagoshima, Japan
    • Aoyama Gakuin University
      • Department of Physics and Mathematics
      Tokyo, Tokyo-to, Japan
  • 2007
    • Japan Atomic Energy Agency
      • Quantum Beam Science Directorate
      Muramatsu, Niigata, Japan
  • 2006–2007
    • Keio University
      • Department of Applied Physics and Physico-Informatics
      Tokyo, Tokyo-to, Japan
  • 2001–2003
    • Saitama University
      • Department of Physics
      Saitama, Saitama, Japan
    • Yale University
      New Haven, Connecticut, United States
    • Centro Brasileiro de Pesquisas Físicas
      Rio de Janeiro, Rio de Janeiro, Brazil
  • 2001–2002
    • University of Mississippi
      Mississippi, United States
  • 1970–2001
    • University of Wisconsin–Madison
      Madison, Wisconsin, United States
  • 1988–1999
    • Aichi Institute of Technology
      Okazaki, Aichi, Japan
    • Rochester General Hospital
      Rochester, New York, United States
  • 1998
    • Kyoritsu College of Pharmacy
      • Department of Biochemistry
      Edo, Tōkyō, Japan
    • Tottori University
      • Department of Electrical and Electronic Engineering
      Tottori, Tottori-ken, Japan
  • 1997
    • Nagoya University
      Nagoya, Aichi, Japan
    • Yokkaichi University
      Nagoya, Aichi, Japan
  • 1990–1995
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 1993
    • Toyota Technological Institute
      Nagu, Okinawa, Japan
  • 1989
    • Teikyo University Hospital
      Edo, Tōkyō, Japan
  • 1981
    • Nagasaki University Hospital
      Nagasaki, Nagasaki, Japan