研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 宇宙物理学研究系 准教授総合研究大学院大学 物理科学研究科 宇宙科学専攻 准教授特定国立研究開発法人理化学研究所 光量子工学研究センター 時空間エンジニアリング研究チーム 客員研究員
- 学位
- 博士(理学)(2001年3月 東京大学)
- 研究者番号
- 50334248
- ORCID ID
https://orcid.org/0000-0003-3529-3029- J-GLOBAL ID
- 200901059420620376
- researchmap会員ID
- 1000367787
- 外部リンク
委員歴
1-
2006年11月 - 2007年10月
論文
245-
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT 59(169) 229-233 2007年 査読有りWe report about the Suzaku observation of two ultraluminous X-ray sources (ULXs), X-1 and X-2, in NGC1313, together with their spectra by XMM-Newton. During the observation, both showed intensity-correlated spectral changes. The brighter source, X-1, exhibited the highest luminosity (similar to 3 x 10(40) erg s(-1)) ever recorded from this source. Its spectral variation is ascribed to a strong power-law like component with a mild high energy curvature, while about 10% of the flux is carried by a stable soft component modeled by a cool disk emission. These properties suggest that the source was in the "very high" state, wherein the disk emission is strongly Comptonized and the optically-thick disk is truncated at a large radii or cooled off. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor disk model with the innermost disk temperature of 1.2-1.3 keV, and becomes flatter as the source gets brighter. Hence X-2 is interpreted to be in a slim disk state. These results suggest that the two ULXs host black holes of a few tens to a few hundreds solar masses.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S1-S7 2007年1月 査読有りHigh-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S151-S161 2007年1月 査読有りWe studied extended X-ray emission from the Carina Nebula taken with the Suzaku CCD camera XIS on 2005 August 29. The X-ray morphology, plasma temperature, and absorption to the plasma are consistent with the earlier Einstein results. The Suzaku spectra newly revealed emission lines from various species, including oxygen, but not from nitrogen. This result restricts the N/O ratio to be significantly low, compared with evolved massive stellar winds, suggesting that the diffuse emission originated in an old supernova remnant or a super shell produced by multiple supernova remnants. The X-ray spectra from the north and south of eta Car showed distinct differences between 0.3-2 keV. The south spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon ions, while the north spectrum shows them weak in intensity. This means that the silicon and iron abundances are a factor of 2-4 higher in the south region than in the north region. The abundance variation may be produced by an SNR ejecta, or related to dust formation around the star-forming core.
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 92-96 2007年 査読有りWe present the result of the Suzaku observation at the northeastern limb of the Cygnus Loop supernova remnant. The high detection efficiency together with the high spectral resolution of the Suzaku X-ray CCD camera enables us to detect highly-ionized C and N emission lines from the Cygnus Loop for the first time. Since there is a significant plasma structure over the field of view, we selected the softest region based on the ROSAT observation. The data are well characterized by a two-component non-equilibrium ionization model with different values of electron temperature. Abundances of C to Fe are all depleted to typically 0.3 solar except O. We found that the optical depth effect for resonance lines for O plays an important role in the X-ray emission of the Cygnus Loop.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S199-S208 2007年1月 査読有りWe observed the bright unidentified TeV gamma-ray source HESS J1616-508 with the X-ray Imaging Spectrometers onboard the Suzaku satellite. No X-ray counterpart was found to a limiting flux of 3.1 x 10(-13) erg s(-1) cm(-2) in the 2-10 keV band, which is some 60-times below the gamma-ray flux in the 1-10 TeV band. This object is bright in TeV gamma-rays, but very dim in the X-ray band, and thus is one of the best examples in the Galaxy of a "dark particle accelerator." We also detected soft thermal emission with kT similar to 0.3-0.6 keV near the location of HESS J1616-508. This may be due to a dust-grain scattering halo from the nearby bright supernova remnant RCW 103.
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2007 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-11 4 2526-+ 2007年 査読有りWe report in-flight status of the X-ray detectors on board the Suzaku observatory, the 5th X-ray astronomy satellite of Japan launched on July 10, 2005. Suzaku is equipped with two types of instruments: one is the X-ray Imaging Spectrometers (XISs) and the other is Hard X-ray Detector (HXD). XIS utilizes the X-ray CCD camera in combination with the grazing-incidence X-ray telescope. HXD is a non-imaging, hybrid detector utilizing Si PIN diodes and GSO/BGO phoswich counters. Suzaku takes a low-earth, circular orbit with an altitude of 560 km and an inclination of 31 deg. This means that Suzaku goes through the south atlantic anomaly about 1/3 of its revolutions. This has a large impact on the in-flight performance of XIS and HXD, which is reported in detail in the present paper.
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ADVANCES IN SPACE RESEARCH 40(8) 1255-1258 2007年 査読有りSuzaku launched in July 2005 is equipped with the wideband instruments covering 0.3-700 keV. In addition to these main instruments, active shield counters of the hard X-ray detector are designed to be a wideband all-sky monitor (WAM). The WAM is a powerful gamma-ray burst monitor with a wide energy range of 50-5000 keV and with a large effective area of 400cm(2) even around 1 MeV. The paper describes the strategy for the prompt GRB observation with the WAM, and the follow-up observation of X-ray afterglows with the narrow field instruments. So far, the WAM has detected 53 GRBs and half of them were detected simultaneously with other satellites. In addition to that, from at least 8 GRBs, including a bright and hard GRB 051008, it is succeeded to observe significant gamma-ray emission up to 1 MeV. The X-ray afterglow observations were carried out on January 5 and on September 4, 2006. Their results are reported in separate paper. (c) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.
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FIRST GLAST SYMPOSIUM 921 106-+ 2007年 査読有りThe wide-band all-sky monitor (WAM) onboard Suzaku has the largest effective area in 300-5000 keV, and thus very powerful to constrain the E peak and high energy tail of gamma-ray burst prompt emission. Collaboration with GLAST will give us high-quality data of gamma-ray prompt emissions to probe and resolve the emission mechanism and central engine of gamma-ray bursts. Here we report initial results of the WAM and address on the collaboration with GLAST.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S53-S76 2007年1月 査読有りThe in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600keV, energy resolutions of similar to 4 keV (FWHM) at 40 keV and similar to 11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 109-112 2007年 査読有りThe Galactic center (GC) region has been known to exhibit strong enhancements of hot diffuse plasma, which is characterized by the highly ionized Fe-K fluorescence line. Based on past X-ray observations with Ginga, ASCA, and RXTE, in the Galactic plane or bulge region, a non-thermal emission, so-called the "hard-tail", has been confirmed to dominate the hard X-ray flux above 10 keV, and an association was found between surface brightnesses of the thermal and non-thermal components despite the completely different emission mechanism. Therefore, it is obviously important to investigate an existence of the hard-tail at GC with the unprecedented sensitivity of the HXD onboard Suzaku. By combining its narrow field-of-view of 30' and X-ray images simultaneously obtained by the XIS below 10 keV, an extensive investigation of spectral and spatial properties of the GC hard X-ray emission can be for the first time realized. We will report on results from seven pointings around GC, with a total exposure of 300 ks, performed in the performance verification phase of Suzaku. Strong hard X-ray signals were clearly detected in every observation by HXD-PIN in 10-70 keV range with a few tenth mCrab level intensities.
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Publications of the Astronomical Society of Japan 59(1 SPEC. ISS.) S283-S299 2007年1月 査読有り
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 142-145 2007年 査読有りSN 1006 is the milestone of understanding the acceleration mechanism of cosmic rays, and this year is the millennium year for the remnant. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) onboard Suzaku satellite. Thanks to the excellent spectral response of XIS, K emission lines from highly ionized oxygen were clearly resolved. The intensity maps of these lines have been made additional to the intensity and photon index maps of the nonthermal component. We discovered that regions with strong and hard nonthermal component has weak thermal emission. The north rim of the SNR has the hardest nonthermal component. These facts might have information of efficient cosmic ray acceleration and background plasma.
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 157-161 2007年 査読有りWe report on results from Suzaku broadband X-ray observations of the Galactic supernova, remnant (SNR) RX J1713.7-3946 with an energy coverage of 0.4-40 keV. With a sensitive hard X-ray measurement from the HXD PIN on board Suzaku, we determine the hard X-ray spectrum in the 12-40 keV range to be described by a power law with photon index Gamma = 3.2 +/- 0.2, significantly steeper than the soft X-ray index of Gamma = 2.4 +/- 0.05 measured previously with ASCA and other missions. We find that a simple power law fails to describe the full spectral range of 0.4-40 keV and instead a cutoff power law with bard index Gamma = 1.96 +/- 0.05 and high energy cutoff epsilon(c) = 9 +/- 1 keV provides an excellerit fit over the full bandpass.
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PROCEEDINGS OF SICE ANNUAL CONFERENCE, VOLS 1-8 3010-3015 2007年 査読有りDeveloping the observation technology in space astronomy science, to realize accurate pointing control and/or to determine accurate direction of the observing objects are strongly required. However, it is difficult to be free from the problem of the distortion of the satellite structure or the telescope itself that is induced by thermally or other complex phenomena. These distortion cause analysis error in the observation analysis. This paper proposes a solution. In this scheme, several displacement-measuring equipments are introduced and the outputs of this monitor system are sending to ground-station. This scheme is assuming the linearity of the relation between the distortion and observed results by mission instrument (such as space telescope). Once this basic assumption is accepted, it becomes to be able to use mathematical linear theory for alignment analysis. As the results, it enables to compensate observing data to perform the calibration operation in orbit.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S215-S220 2007年1月 査読有りDuring an observation of the Galactic plane in the Scutum region with the Suzaku satellite, we discovered a new X-ray transient source, designated Suzaku J1844-0404. Compared with previous Chandra observations of the same field, four Chandra X-ray sources exist within the current positional uncertainty of Suzaku J1844-0404. A firm identification is not possible. From the beginning of the observation, the X-ray intensity was significant at similar to 5 x 10(-14) erg s(-1) cm(-2) (2-10 keV), which may be a possible precursor. Later, the source exhibited a flare with a peak flux of similar to 10(-12) erg s(-1) cm(-2) (2-10 keV). A strong and narrow emission line at similar to 6.66 keV was observed during the flare, most likely the He-like Fe line. The spectrum in 1-10 keV is consistent with a heavily absorbed (N-H similar to 3 x 10(22) H cm(-2)) thin thermal emission with kT as high as similar to 7 keV. A single short flare, as observed, is rather unlikely for a cataclysmic variable. The source is probably an active binary star or a young stellar object.
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Proceedings of the 30th International Cosmic Ray Conference, ICRC 2007 1(SH) 745-748 2007年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S171-S176 2007年1月 査読有りThe newly operational X-ray satellite Suzaku observed the southwestern quadrant of the supernova remnant RCW 86 in 2006 February to study the nature of the 6.4 keV emission line first detected with the Advanced Satellite for Cosmology and Astronomy (ASCA). The new data confirm the existence of the line, localizing it for the first time; most of the line emission is adjacent and interior to the forward shock, and not at the locus of the continuum hard emission. We also report the first detection of a 7.1 keV line, which we interpret as K beta emission from low-ionization iron. The Fe K line features are consistent with a non-equilibrium plasma of Fe-rich ejecta with n(e)t less than or similar to 10(9) cm(-3) s and kT(e) similar to 5 keV. This combination of low n(e)t and high kT(e) suggests collisionless electron heating in an SNR shock. The Fe K alpha line shows evidence for intrinsic broadening, with a width of 47 (34-59) eV (99% error region). The difference in the spatial distributions of the hard continuum above 3 keV and the Fe K line emission supports a synchrotron origin for the hard continuum.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S53-S76 2007年1月 査読有りThe in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600keV, energy resolutions of similar to 4 keV (FWHM) at 40 keV and similar to 11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S163-S170 2007年1月 査読有りWe present the results of a Suzaku observation at the northeastern limb of the Cygnus Loop supernova remnant. The high detection efficiency together with the high spectral resolution of the Suzaku X-ray CCD cameras enables us to detect highly-ionized C and N emission lines from the Cygnus Loop for the first time. We performed an annular spectral analysis to our data set and investigated the plasma structure along the radial direction. Our data are well characterized by a two-component non-equilibrium ionization model with different values of electron temperature. Abundances of C to Fe are all depleted to typically 0.1 solar, even for Ne. Relative abundances to O are roughly consistent with solar values.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(1 SPEC. ISS.) S209-S214 2007年1月 査読有りSuzaku deep observations have discovered two highly significant nonthermal X-ray sources, Suzaku J1804-2142 (Src 1) and Suzaku J1804-2140 (Src 2), positionally coincident with the unidentified TeV gamma-ray source, HESS J1804-216. The X-ray sources are not time variable and show no Counterpart in other wavebands, except for the TeV source. Src 1 is unresolved at Suzaku spatial resolution, whereas Src 2 is extended or composed of multiple sources. The X-ray spectra are highly absorbed, hard, and featureless, and are well fitted by absorbed power-law models with best-fit photon indices and absorption columns of -0.3(-0.5)(+0.5) and 0.2(-0.2)(+2.0) x 10(22) cm(-2) for Src 1, and 1.7(-1.0)(+1.4) and 1.1(-0.6)(+1.0) x 10(23) cm(-2) for Src 2. The measured X-ray absorption to the latter source is signif icantly larger than the total Galactic neutral hydrogen column in that direction. The unabsorbed 2-10 keV band luminosities are 7.5 x 10(32) (d/5 kpc)(2) erg s(-1) (Src 1) and 1.3 x 10(33) (d/5 kpc)(2) erg s(-1) (Src 2), where d is the source distance. Among the handful of TeV sources with known X-ray counterparts, HESS J1804-216 has the largest ratio of TeV gamma-ray to hard X-ray fluxes. We discuss the nature of the emission and propose the Suzaku sources as plausible counterparts to the TeV source, although further observations are necessary to confirm this.
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HEATING VERSUS COOLING IN GALAXIES AND CLUSTERS OF GALAXIES 2007 398-+ 2007年 査読有りWe carried out observations of the central and 20' east offset regions of the cluster of galaxies Abell 1060 with Suzaku. Spatially resolved X-ray spectral analysis has revealed temperature and abundance profiles of Abell 1060 out to 27' similar or equal to 380 h(70)(-1) kpc, which corresponded to similar to 0.3 r(vir). The temperature decrease of the intra cluster medium from 3.4 keV at the center to 2.2 keV in the outskirt region are clearly observed. Si, S and Fe abundances also decrease by more than 50% from the center to the outer parts, while Mg shows a fairly constant abundance of similar to 0.7 solar within r < 17'. O shows a lower abundance of similar to 0.3 solar in the central region (r < 6'), and indicates a similar feature with Mg, however it is sensitive to the estimated contribution of the Galactic components at the outer annuli (r > 13'). Results on temperature and abundances of Si, S, and Fe are consistent with those derived by XMM-Newton at r < 13'. The formation and metal enrichment of the cluster are discussed based on implications of our results.
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IEEE Nuclear Science Symposium Conference Record 2 783-787 2007年 査読有りSuzaku is the fifth Japanese astrophysical satellite, devoted to study high energy phenomena in the X-ray band of 0.5 - 600 keV. It was successfully launched from Uchinoura Space Center in Japan on 10th July 2005. The HXD on board Suzaku covers 10 - 600 keV band with a high sensitivity of about 10 -5 cnt/s/cm2/keV level. The sensor consists of 16 identical GSO/BGO well-type-phoswich counters incorporating 2 mm-thick silicon PIN diodes, and 20 surrounding-BGO-shield counters to remove residual non X-ray backgrounds through anti-coincidence rejection. The present paper is particularly focused on timing system of the HXD and in-orbit verifications with pulsars. © 2006 IEEE.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(2) 299-317 2007年1月 査読有り
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NIM-A 579 23-26 2007年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S35-S51 2007年1月 査読有りThe Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by the combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit background based on a combination of new techniques, including the concept of a well-type active shield counter. With an effective area of 142 cm(2) at 20 keV and 273 cm(2) at 150 keV, the background level at sea level reached similar to 1 X 10(-5) cts s(-1) cm(-2) keV(-1) at 30 keV for the PIN diodes, and similar to 2 X 10(-5) cts s(-1) cm(-2) keV(-1) at 100 keV, and similar to 7 X 10(-6) cts s(-1) cm(-2) keV(-1) at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of similar to 4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (similar to 5 degrees). The on-board signal-processing system and the data transmitted to the ground are also described.
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PASJ : publications of the Astronomical Society of Japan 59(1) S257-S267 2007年1月 査読有りTwo ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313, named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the observation for a net exposure of 28 ks (but over a gross time span of 90 ks), both objects varied in intensity by about 50%. The 0.4–10 keV X-ray luminosities of X-1 and X-2 were measured as 2.5×1040 ergs-1 and 5.8×1039 ergs-1, respectively, with the former exhibiting the highest ever reported for this ULX. The spectrum of X-1 can be explained by the sum of a strong and variable powerlaw component with a high-energy cutoff, and a stable multicolor blackbody with an innermost disk temperature of ∼ 0.2keV. These results suggest that X-1 was in a "very high" state, where disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1 is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best represented, in its fainter phase, by a multicolor blackbody model with an innermost disk temperature of 1.2–1.3 keV, and becomes flatter as the source becomes brighter. Hence, X-2 is interpreted to be in a slim-disk state. These results suggest that the two ULXs have black hole masses of some dozens to a few hundred of solar masses.
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ASPC vol. 361 p533-535 2007年 査読有り
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The discovery of diffuse X-ray emission in NGC 2024, one of the nearest massive star-forming regionsASTROPHYSICAL JOURNAL 649(2) L123-L128 2006年10月 査読有りWe analyzed deep 75 ks Chandra ACIS-I data of NGC 2024 with the aim of searching for diffuse X-ray emission in this most nearby (415 pc) of massive star-forming regions. After removing point sources, extended emission was detected in the central circular region with a radius of 0.5 pc, and it is spatially associated with this young massive stellar cluster. Its X-ray spectrum exhibits a very hard continuum (kT > 8 keV) and shows signs of having a He-like Fe K alpha line with a 0.5-7 keV absorption-corrected luminosity of 2 x 10(31) ergs s(-1). Undetected faint point sources, estimated from the luminosity function of the detected sources, contribute less than 10% to this emission. Hence, the emission is truly diffuse in nature. Because of the proximity of NGC 2024 and the long exposure, this discovery is one of the strongest pieces of evidence in support of the existence of diffuse X-ray emission in massive star-forming regions.
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NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA B-GENERAL PHYSICS RELATIVITY ASTRONOMY AND MATHEMATICAL PHYSICS AND METHODS 121(10-11) 1127-1131 2006年10月 査読有りThe Wideband All-sky Monitor (WAM) onboard Suzaku is a very powerful Gamma-Ray Burst (GRBs) monitor, thanks to its very wide energy range of 50 keV-5 MeV and large effective area of 400 cm(2) even at 1 MeV. GRB observations with the WAM enable us to study the high-energy tail of the distribution of the E-peak and to explore the hard emission tail around MeV energy region. The WAM has already detected 126 GRBs from 2005 August to 2006 August and some of them were also detected simultaneously with other GRB satellites. The GRB detection rate is about 120 per year, in agreement with that expected before launch. The duration distribution of GRBs obtained with the WAM is bimodal, which is consistent with the BATSE results. Here we report the preliminary results of the GRB spectral properties up to MeV energy region, such as the E-peak distribution, the E-peak-E-iso correlation, and the spectral evolution.
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IEEE Transactions on Nuclear Science 53(5) 2983-2990 2006年10月 査読有り
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ASTROPHYSICAL JOURNAL 648(2) L139-L142 2006年9月 査読有りThe binary X-ray pulsar A0535 + 262 was observed with the Suzaku X-ray observatory on 2005 September 14 for a net exposure of 22 ks. The source was in the declining phase of a minor outburst, exhibiting 3-50 keV luminosity of similar to 3.7 x 10(35) ergs s(-1) at an assumed distance of 2 kpc. In spite of the very low source intensity ( about 30 mcrab at 20 keV), its electron cyclotron resonance was detected clearly with the Suzaku Hard X-Ray Detector, in absorption at about 45 keV. The resonance energy is found to be essentially the same as that measured when the source is almost 2 orders of magnitude more luminous. These results are compared with the luminosity-dependent changes in the cyclotron resonance energy, observed from 4U 0115 + 63 and X0331 + 53.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 53(4) 2404-2408 2006年8月 査読有りThe temperature dependence (from -20 to +20 degrees C) of gamma-ray irradiated light outputs, energy resolutions, and decay time profiles of three YAG:Ce poly-ceramic scintillators are studied. The Ce concentrations are 0.5, 0.05, and 0.005 mol%. The relative light yield of the YAG:Ce with 0.5 mol% with a 2 mu s shaping time was measured as 1:1.08:1.14 at +20, 0, and -20 degrees C, respectively, including the temperature dependence of the phototube (-0.2%/degree). The energy resolution stays almost constant at 7.2%, for 662 keV gamma-rays. The ceramic with 0.05 mol% shows the almost same properties, while the light yield of that with 0.005 mol% is 2-4 times lower (hence the energy resolution becomes 14-19%). All the scintillators exhibit good linearities within similar to 1% between the light output and the irradiated gamma-ray energy from 59.5 keV to 662 keV. The decay time constants of the dominant decay components are about 80 ns and 300 ns at +20 degrees C. As the temperature increases from -20 to +20 degrees C, the effective decay of all the ceramics becomes faster, because the decay time constants and fractions of the slower components shorten and decrease, respectively. This result suggests that carriers which are captured in shallow traps before transferring excitation to Ce ions can escape the traps more easily at higher temperatures. Considering the decrease of the total light yield toward higher temperatures, it is thought that thermal quenching starts to dominate the temperature dependence of the ceramic YAG:Ce around the room temperature. The 0.5 mol% scintillator shows a lower quenching energy than the 0.05 mol% one. This can be explained in terms of self absorption of Ce emission.
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ASTROPHYSICAL JOURNAL 647(2) L131-L134 2006年8月 査読有りBD + 30 3639, the brightest planetary nebula at X-ray energies, was observed with Suzaku, an X-ray observatory launched on 2005 July 10. Using the X-ray Imaging Spectrometer, the K lines from C VI, O VII, and O VIII were resolved for the first time, and the C/O, N/O, and Ne/O abundance ratios were determined. The C/O and Ne/O abundance ratios exceed the solar value by factors of at least 30 and 5, respectively. These results indicate that the X-rays are emitted mainly by helium-shell-burning products.
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Bulletin of the American Astronomical Society 38 149-149 2006年6月
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Proceedings of the International Astronomical Union 2(234) 165-168 2006年4月 査読有り
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ASTROPHYSICAL JOURNAL 638(2) 860-877 2006年2月 査読有りChandra ACIS-I data of the molecular cloud and H II region complex NGC 6334 were analyzed. The hard X- ray clumps detected with ASCA (Sekimoto and coworkers) were resolved into 792 point sources. After removing the point sources, an extended X- ray emission component was detected over a 5; 9 pc2 region, with the 0.5-8 keV absorption-corrected luminosity of 2; 1033 ergs s(-1). The contribution from faint point sources to this extended emission was estimated as at most similar to 20%, suggesting that most of the emission is diffuse in nature. The X- ray spectrum of the diffuse emission was observed to vary from place to place. In tenuous molecular cloud regions with hydrogen column density of ( 0: 5 1); 10(22) cm(-2), the spectrum can be represented by a thermal plasma model with temperatures of several keV. The spectrum in dense cloud cores exhibits harder continuum, together with higher absorption of more than similar to 3; 10(22) cm(-2). In some of such highly obscured regions, the spectra show extremely hard continua equivalent to a photon index of similar to 1, and favor a nonthermal interpretation. These results are discussed in the context of thermal and nonthermal emission, both powered by fast stellar winds from embedded young early-type stars through shock transitions.
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GAMMA-RAY BURSTS IN THE SWIFT ERA 836 201-+ 2006年 査読有りThe Suzaku Wide-band All-sky Monitor (WAM), realized by large thick anti-coincidence shields of the Hard X-ray Detector (HXD), can be powerful gamma-ray burst (GRB) detector which is sensitive to 50-5000 keV gamma-rays. The WAM is now in a full operational phase, and we have already detected some GRBs simultaneously with other satellites (Swift, Konus-Wind, HETE2 and INTEGRAL SPI/ACS). The most impressive event among detected GRBs is GRB051008, which was detected up to 2 MeV with the WAM. In this paper, we report on the WAM in-flight performance as a GRB monitor from initial three-months operations, focusing on the GRB trigger status and spectral analysis of GRB051008 and GRB051111 combined with Swift.
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International Conference Recent Advances in Natural Language Processing, RANLP 2006年 査読有り
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Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray, Pts 1 and 2 6266 L2662-L2662 2006年 査読有りThe hard X-ray detector (HXD) onboard Suzaku covers an energy range of 8-700 keV, and thus in combination with the CCD camera (XIS) gives us an opportunity of wide-band X-ray observations of celestial sources with a good sensitivity over the 0.3-700 keV range. All of 64 Si-PIN photo diodes, 16 GSO/BGO phoswich scintillators, and 20 anti-coincidence BGO scintillators in the HXD are working well since the Suzaku launch on July 2005. The rejection of background events is confirmed to be as effective as expected, and accordingly the HXD achieved the lowest background level of the previously or currently operational missions sensitive in the comparable energy range. The energy and angular responses and timing have been continuously calibrated by the data from the Crab nebula, X-ray pulsars, and other sources, and at present several % accuracy is obtained. Even though the HXD does not perform simultaneous background observations, it detected weak sources with a flux as low as similar to 0.5 mCrab; stars, X-ray binaries, supernova remnants, active galactic nuclei, and galaxy clusters. Extensive studies of background subtraction enables us to study weaker sources.
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Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray, Pts 1 and 2 6266 26643-26643 2006年 査読有りThe X-ray astronomical satellite Suzaku was successfully launched in July 2005. The onboard Wideband All-sky Monitor (WAM) is designed as the second function of the large, thick BGO anti-coincidence shields of the Hard X-ray Detectors (HXD). It views about half of the whole sky and has a geometrical area of 800 cm(2) per side, with a large effective area of 400 cm(2) even at 1 MeV. Hence, the WAM is expected to provide unique opportunities to detect high energy emission from GRBs and solar flares in the MeV range. In fact, the WAM has detected at least 47 GRBs, although the fine-tuning of the GRB functions is still in progress. The most impressive GRB result is the bright, hard spectrum GRB 051008, which was detected up to 1 MeV with the WAM. We will present here the in-flight performance of the HXD/WAM during the initial eight-months of operations. The in-flight energy response, spectral and timing capabilities, and in-orbit background are described in this paper.
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HARD X-RAY AND GAMMA-RAY DETECTOR PHYSICS AND PENETRATING RADIATION SYSTEMS VIII 6319 2006年 査読有りThe hard X-ray detector (HXD-II) is one of the scientific payloads onboard Suzaku, the 5th Japanese cosmic Xray satellite. After the launch in July 2005, all the HXD-II components, including the sensors and analog/digital electronics, have been working normally. In order to archive the maximum performance of the HXD-II, especially the GSO/BGO well-type phoswich counters, extensive in-orbit qualification and calibration have been carried out utilizing the data acquired in early operations. Major items of these efforts include; to estimate the circuit dead time, calibrate energy scale, optimize the event selection criteria for background reduction, study the background, and examine the detector response. As a result of these in-orbit calibrations, the HXD-II background in the 10 similar to 600 keV range has been successfully lowered to (0.5 similar to 5.0) x 10(-4) c s(-1)keV(-1)cm(-2). This is the lowest among the background ever achieved in orbit by cosmic hard X-ray detectors.
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2006 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOL 1-6 2 783-787 2006年 査読有りSuzaku is the fifth Japanese astrophysical satellite, devoted to study high energy phenomena in the X-ray band of 0.5 - 600 keV. It was successfully launched from Uchinoura Space Center in Japan on 10th July 2005. The HXD on board Suzaku covers 10 - 600 keV band with a high sensitivity of about 10(-5) cnt/s/cm(2)/keV level. The sensor consists of 16 identical GSO/BGO well-type-phoswich counters incorporating 2 mm-thick silicon PIN diodes, and 20 surrounding-BGO-shield counters to remove residual non X-ray backgrounds through anti-coincidence rejection. The present paper is particularly focused on timing system of the HXD and in-orbit verifications with pulsars.
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SPACE TELESCOPES AND INSTRUMENTATION II: ULTRAVIOLET TO GAMMA RAY, PTS 1 AND 2 6266 2006年 査読有り
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52(6) 2758-2764 2005年12月 査読有りThe hard X-ray detector (HXD-II) onboard Astro-E2 consists of a main detector with energy range 10-600 keV and a BGO active shield detector for background reduction. The shield detector wide-band all-sky monitor (WAM) has been designed not only for background reduction but also for all sky monitoring of gamma-ray bursts (GRB) and bright soft gamma-ray sources. WAM has a large geometrical structure of BGO scintillators for reinforcing its stopping power and has an asymmetric shape for reducing its weight. This particular structure of WAM makes the gamma-ray response very complicated, and thus we need careful calibrations before the launch. We then performed preflight calibrations of WAM as a part of the HXD-II calibrations in 2003-2004. We measured the pulse height spectra and stopping power of each unit counter individually before the HXD-II integration by exposing them to collimated gamma-rays. After integration of the HXD-II detector and installing it to the spacecraft, we measured the same issues as above for WAM by irradiating the gamma-ray source from various directions. Taking into account these experimental results, we constructed the gamma-ray response matrix of WAM using the Geant4 Monte Carlo simulation. The response developed in this work was found to have reproduced the experimental data within 10-20% accuracy.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52(6) 2749-2757 2005年12月 査読有りThe soft gamma-ray detector (SGD) onboard the Japanese future high energy astrophysics mission (NeXT) is a Compton telescope with narrow field of view, which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and cadmium telluride (CdTe) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 x 10(-7) counts/s/cm(2) /keV; the silicon layers are required to improve the performance at a lower energy band (< 0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing it to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD: high quality CdTe, low noise front-end application-specific integrated circuit, and bump bonding technology. Energy resolutions of 1.7 keV (full-width at half-maximum) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of Monte Carlo simulation used to evaluate the performance of the SGD.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52(6) 2765-2772 2005年12月 査読有りThe hard X-ray detector (HXD-II) is one of the three scientific instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled to be launched in 2005. This mission is very unique in a point of having a lower background than any other past missions in the 10-600 keV range. In the HXD-II, the large and thick BGO crystals are used as active shields for particle and gamma-ray background to the main detector. They have a wide field of view of similar to 2 pi and a large effective area of 400 cm(2) even at 1 MeV. Hence, the BGO shields have been developed as a wide-band all-sky monitor (WAM) with a broadband coverage of 50-5000 keV. In this paper, overall design and performance of the HXD-II/WAM based on the results of preflight calibration tests carried out in June 2004 are described. By irradiating various radio isotopes with the WAM flight model, we verified that it had comparable capabilities with other gamma-ray burst detectors.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52(5) 2052-2057 2005年10月 査読有りEmploying Fourier-synthesis optics and one-dimensional position-sensitive detectors, we are developing a novel hard X-ray imager which can work in the similar to 10 keV to similar to 200 keV range either as a telescope or a microscope. As the detection part of our imager, we have developed a strip detector made of Schottky CdTe diode, with its cathode divided into 64 channels of 150 mu m pitch. Electrodes of all channels are gold-stud bonded to a fanout board, and connected to low noise analog ASIC. We read out signals from all channels simultaneously. As the grid optics elements, one-dimensional "modulation collimator" grids of 1 mm thick tungsten have been manufactured, with 10 grid pitches ranging from 0.2 mm to 2 mm with harmonic ratios. Combining the CdTe strip detector and the grids, we have verified hard X-ray imaging performance of this system. Using an Am-241 source, we have successfully obtained an image in the 10-70 keV range with a spatial resolution of similar to 0.5 mm.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52(5) 1836-1841 2005年10月 査読有りWe measured basic properties of three ceramic Y3Al5O12 (YAG) scintillators doped with Ce to a concentration of 0.5, 0.05, and 0.005 mol%, in comparison with a monocrystalline YAG scintillator with unknown amount of Ce doping. First, optical transparency and emission spectra were investigated. We confirmed that the transparency of the ceramics is comparable to that of the monocrystalline one (similar to 80%) in wavelengths longer than similar to 500 nm. The ceramics did not show an indication of lattice defects which is present in the monocrystalline YAG. Then the response to gamma-rays was studied using a phototube as a scintillation light detector. The 0.5 mol% sample exhibited the highest light yield (similar to 40% of CsI), with an energy resolution of about 7.2% at Cs-137 662 keV photoabsorption peak. The optimum Cc concentration for a similar to 2 mm thick ceramic YAG was determined to be similar to 0.1 mol%. Using the delayed coincidence method, the principal time constant of the ceramic YAGs was measured as similar to 80 ns. By irradiating 5.49 MeV alpha-particles, the alpha-ray to gamma-ray light yield ratio of the ceramic YAGs was found to depend negatively on the amount of Cc; namely, 0.28, 0.20, and 0.13 in the increasing order of the Ce concentration. The 200-1000 keV intrinsic background of the 0.5 mol% ceramic was similar to 10(-5) counts/s/cm(3), indicating that it is not significantly contaminated by radioactive impurities.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 52(4) 902-909 2005年8月 査読有りThe Hard X-ray Detector (HXD-II) is one of the scientific payloads on board the fifth Japanese cosmic X-ray satellite Astro-E2, scheduled for launch in 2005. The HXD-II is designed to cover a wide energy range of 10-600 keV with a high sensitivity of about 10(-5) cnt/s/cm(2) /keV. In order to derive the energy response of the sensor and to estimate the background, a Monte Carlo simulator based on the Geant4 toolkit is currently being developed. This paper describes the design concept of the HXD-II software package, including the analysis tools and the Monte Carlo simulator, and its verification through a comparison with actual data taken by pre-flight radio-isotope irradiation experiments, together with calculated outputs that can demonstrate the in-orbit performance of the HXD-II.
MISC
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JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS 4(2) 2018年4月 査読有り
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日本物理学会講演概要集(CD-ROM) 73(1) ROMBUNNO.25pK307‐5-492 2018年3月23日
共同研究・競争的資金等の研究課題
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