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 助教総合研究大学院大学 宇宙観測科学講座 飛翔体天文学分野 助教
- 学位
- 博士(理学)(1998年3月 京都大学)修士(理学)(1995年3月 京都大学)
- 研究者番号
- 80342624
- ORCID ID
https://orcid.org/0000-0002-9099-5755- J-GLOBAL ID
- 202001011170717781
- researchmap会員ID
- R000011919
論文
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Chinese Journal of Astronomy and Astrophysics 2003年12月31日
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ASTRONOMISCHE NACHRICHTEN 324 167-172 2003年9月A deep observation toward the Galactic center with the Chandra X-Ray Observatory revealed a number of extended features, in addition to Sgr A* and SgrA East. Here, we focus on two curious, extended X-ray structures: large-scale (similar to 10 pc) bipolar lobes centered on Sgr A* and a bright cometary source located 0.3 pc from Sgr A*, CXOGC J174539.7-290020. The bipolar lobes consist of a number of emission clumps oriented along a line perpendicular to the Galactic plane, suggesting that a series of ejections has taken place on characteristic time scales of hundreds to thousands of years. The clumps are embedded in a low-intensity, edge-brightened lobe which is most evident in a flux ratio map. At two locations along the lobe, nonthermal linear features are present, suggesting that relativistic electrons may be impinging on the compressed, magnetic wall of this structure. The cometary X-ray source has no counterpart at other wavelengths; its orientation is consistent with a high-velocity neutron star ejected from the grouping of stars at IRS13, but there are problems with that hypothesis, and other models warrant consideration.
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ASTRONOMISCHE NACHRICHTEN 324 125-131 2003年9月We have found strong 6.4-keV line emissions from the giant molecular clouds in the Galactic center region: Sgr B2, Sgr C, and M0.11-0.08 (at the Radio Arc region). The high angular resolution of Chandra reveals that the 6.4-keV line emissions are indeed coincident with the clouds, and shifted towards the Galactic center. The X-ray spectra have very strong 6.4-keV lines with equivalent widths >= 1 keV and are attenuated by larger column densities of interstellar gas. These characteristics imply that the massive molecular clouds are irradiated by an external X-ray source in the direction of the Galactic center and emit fluorescent and scattered X-rays. These clouds are new category of X-ray source: "X-ray Reflection Nebula".The reflected X-ray flux reveals the recent luminosity history of the primary irradiating source, which may be the massive black hole Sgr A*, according to the light travel time to each cloud. Making use of the radio determinations of the cloud masses, we find that Sgr A* was as luminous as 10(39) erg s(-1) a few hundred years ago, and has gradually decreased to present value.
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ASTRONOMISCHE NACHRICHTEN 324 407-411 2003年9月Over the last three years, the Galactic center region has been monitored with a series of Chandra/ACIS observations. Besides the target object Sgr A*, the surrounding diffuse X-ray emission has been detected within the 17' x 17' field of view. As of 2002 June, combining all 12 GTO and GO observations, the total effective exposure reaches similar to 590 ks, which reveals the detail structure of the faint filamentary diffuse X-ray emission with significant photon statistics. We here present preliminary results from the imaging/spectral analyses of these data. The "true-color" X-ray image and the equivalent width (EW) images for the detected elemental species of the Galactic center region indicate that the diffuse X-ray features have complex spatio-spectral structures. We detect strong enhancements of He-like Fe within the 1.3' diameter circular region in the immediate east of Sgr A*, which is most likely emission from the highly ionized Fe associated with the supernova remnant Sgr A East. Enhancements of the low ionization state Fe and highly ionized S and Si EWs in the northeast of Sgr A* may be interpreted as irradiation of photons from external X-ray sources and/or emission from bombardments of high energy particles such as unresolved SN ejecta.
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The Astrophysical Journal 2003年7月10日
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CHINESE JOURNAL OF ASTRONOMY AND ASTROPHYSICS 3 297-304 2003年 査読有りThis paper reports the new results of the high energy activity found with the X-ray observations of the Galactic center (GC). The Ginga satellite discovered the largely extended hot plasma around the CC, suggesting a violent activity of the GC within 10(5) year. ASCA found strong 6.4 keV line emissions from the molecular clouds near the CC, which is well explained by the fluorescent caused by strong X-ray irradiations from Sgr A* of similar to 100-300 years ago. Recent Chandra observations on the GC have confirmed these previous results and moreover, with its unprecedented spatial resolution, have resolved a number of non-thermal/6.4-keV X-ray filaments and jet-like structures possibly caused by Sgr A*. We infer that these complexities in morphology and spectrum of the CC X-ray are due to coupled actions of recent supernova explosions, a super massive black hole and giant molecular clouds.
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The Astrophysical Journal 2002年5月10日
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The Astrophysical Journal 2001年9月10日
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Astrophysical Journal 550(1 PART 1) 2001年
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NEW CENTURY OF X-RAY ASTRONOMY 251 298-299 2001年 査読有りWe have carried out a Chandra ACIS-I observation on a typical Galactic plane where no previous X-ray sources have been known. We have discovered more than 50 unidentified sources in the 3-8 keV band above the flux level similar to 3 x 10(-15) ergs/s/cm(2) at the 3 sigma confidence level. The total point source flux accounts for only 10 % of the total X-ray flux in the field of view. The observed source number density shows little excess over the extragalactic log N - log S curve determined from high Galactic latitude regions. The present result indicates that significant parts of the detected sources have extragalactic origin. The Galactic Ridge hard X-ray Emission has truly diffuse origin, and there are few Galactic X-ray sources as dim as similar to 3 x 10(-15) ergs/s/cm(2) (2 - 10 keV).
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 450(2) 360-364 2000年8月11日We have developed a CCD calibration system using fluorescent X-ray lines with energies ranging from 1.49 keV (Al Kα) to 11.2 keV (Se Kα). The absolute X-ray flux is calibrated by a gas proportional counter, while the emerging spectra are monitored by solid-state silicon detectors. In order to suppress contaminating X-rays in the fluorescence spectra, mechanical collimators were set in the X-ray beam line, high-purity targets for fluorescent lines were used, and band-pass filters were put on the X-ray beam line. As for the purity of the fluorescent X-rays, the typical purity achieved was approx. 98%.
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Advances in Space Research 2000年1月
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Astrophysical Journal 534(1 PART 1) 2000年
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Astrophysical Journal 520(1 PART 1) 316-323 1999年7月20日We report the ASCA results of the Great Annihilator 1E 1740.7-2942 obtained with five pointing observations in a time span of 3.5 yr. The X-ray spectrum for each period is well fitted with a single power law absorbed by a high column of gas. The X-ray flux changes by a factor of 2 from period to period, but the other spectral parameters show no significant change. The photon index is flat with T = 0.9-1.3. The column density of hydrogen NH is ∼ 1.0 × 1023 H cm-2 and that of iron NFe is ∼ 1019 Fe cm-2. These large column densities indicate that 1E 1740.7-2942 is near the Galactic center. The column density ratio leads the iron abundance to be 2 times larger than the other elements in a unit of the solar ratio. The equivalent width of the Kα line from a neutral iron is less than 15 eV in 90% confidence. This indicates that the iron column density within several parsecs from 1E 1740.7 -2942 is less than 5 × 1017 Fe cm-2. In addition, the derived hydrogen column density is about one-sixth of that of giant molecular clouds in the line of sight. All these facts support the fact that 1E 1740.7-2942 is not in a molecular cloud, but possibly in front of it; the X-rays are not powered by accretion from a molecular cloud, but from a companion star like ordinary X-ray binaries.
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The Astrophysical Journal 1999年1月10日
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Astronomische Nachrichten 320(4) 325-325 1999年1月
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Advances in Space Research 1999年1月
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Astronomische Nachrichten 320(4-5) 325-325 1999年
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CENTRAL PARSECS OF THE GALAXY 186 586-596 1999年 査読有りWe present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. We found very peculiar features in this cloud; a strong 6.4-keV line emission, a low energy cutoff below 4 keV and a pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak position is shifted from the core of the molecular cloud toward the Galactic Center by about 1-2'. The X-ray spectrum and the morphology are well reproduced by a scenario where X-rays from an external source located in the Galactic Center direction are scattered by the molecular cloud Sgr B2, and come into our line of sight. Thus Sgr B2 is a new type of X-ray object, which may be called an "X-ray reflection nebula". The luminosity of the irradiating source is required to be greater than or equal to 10(38) erg s(-1), but no source has enough brightness. One possibility is that within the recent past, perhaps a few hundred years ago, Sgr A* was very luminous, and we are observing the "reflected" X-rays at present.
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ASTRONOMISCHE NACHRICHTEN 320(4-5) 321-321 1999年 査読有り
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X-RAY TIMING AND COSMIC GAMMA RAY BURSTS 22(7) 997-1001 1998年 査読有りThe bursting pulsar GRO J1744-28 was observed with ASCA on February 26-27, 1996. The source was detected at a persistent flux level of 0.9 Crab with the X-ray bursts followed by a shallow dip. Clear pulsation with apparent barycentric period of 467.054 msec was also detected. Energy spectrum of GRO 51744-28 shows large photoelectric absorption, which is consistent with the location close to the Galactic center. We detected structures in the energy spectrum of the persistent emission around 7 keV. The structure is most probably due to a partial covering of the X-ray emission region. (C) 1998 COSPAR. Published by Elsevier Science Ltd.
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RADIATION FROM BLACK HOLES, FUTURE MISSIONS TO PRIMITIVE BODIES AND MIDDLE ATMOSPHERIC FINE STRUCTURES 19(1) 63-70 1997年 査読有りX-ray imaging and spectroscopic observations near the Galactic Center in the 0.5-10 keV energy band were carried out with the X-ray satellite ASCA. Several X-ray sources were detected. Luminosities of the sources are estimated to be of order 10(35)-10(36) erg s(-1). The largely extended emission with K-shell transition lines from highly ionized atoms were confirmed. Moreover, an extended emission of the 6.4 keV line from the low ionized iron atom was discovered. The 6.4 keV line intensity is elongated to the north-east from the Galactic Center along the galactic plane and well correlates with the distribution of the dense molecular clouds observed in the radio bands. We interpret that the 6.4 keV line originates from the florescent from the molecular cloud irradiated by bright X-ray source. (C) 1997 COSPAR.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 46(3) L125-L129 1994年 査読有りASCA obtained broad-band (0.8-12 keV) images and spectra of the central region of the Rho Ophiuchi dark cloud in 1993 August. The 38-ks observation detected at least eleven sources (S/N greater-than-or-equal-to 3), including the X-ray bright pre-main-sequence star DoAr 21 and embedded infrared sources with no optical counterparts. Hard X-rays up to almost-equal-to 8 keV were detected from DoAr 21 (whose light curve shows no evidence for variability) and from a flaring source lying in a region of high visual extinction. Thermal spectral fits for the brightest source give kT almost-equal-to 2 keV and hydrogen column densities N(H) almost-equal-to 1022 cm-2. The spectrum of a region in the center of the field where no discrete sources were detected shows hard, heavily absorbed emission that is most likely the integrated contribution of a number of deeply embedded young stars below the detection limit.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 46(3) L93-L96 1994年 査読有りASCA observed the Wolf-Rayet binary HD 193793 (WC 7 + O4-5) in 1993 June, only 3 months after periastron passage when the WC star was nearly in front of the 0 star. The X-ray spectra axe heavily absorbed below almost-equal-to 2 keV by the Wolf-Rayet wind and show a prominent emission line from He-like iron at 6.7 keV. A variable abundance Raymond-Smith model gives a temperature of kT almost-equal-to 3 keV (35 million K) and an equivalent hydrogen column density N(H) almost-equal-to 3 x 10(22) cm-2. This column density is a factor of almost-equal-to 10 larger than the interstellar value, confirming that the absorption is primarily circumstellar. We derive an upper limit on the carbon abundance in the WC 7 wind of almost-equal-to 30 solar, and find evidence for a strong overabundance of neon as predicted by evolutionary models. The X-ray luminosity and derived column density agree well with that expected from a colliding wind shock, although comparison with a 1987 Ginga observation fails to reveal the expected change in hard flux (2-6 keV) with binary separation.
MISC
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大気球シンポジウム: 2022年度 = Balloon Symposium: 2022 2022年11月大気球シンポジウム 2022年度（2022年11月7-8日. ハイブリッド開催（JAXA相模原キャンパス& オンライン)) Balloon Symposium 2022 (November 7-8, 2022. Hybrid(in-person & online) Conference (Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan 著者人数: 87名 資料番号: SA6000177030 レポート番号: isas22-sbs-030
講演・口頭発表等
5-
44th COSPAR Scientific Assembly 2022年
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nuclear burning in massive stars – towards the formation of binary black holes – 2021年7月28日
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Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月19日
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The 15th Symposium of Japanese Research Community on X-ray Imaging Optics 2019年10月26日 招待有り
担当経験のある科目(授業)
6-
2023年9月 - 2024年3月
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2021年4月 - 2022年3月宇宙理学概論(オムニパス) (総合研究大学院大学)
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2019年10月 - 2020年3月宇宙理学概論(オムニパス) (総合研究大学院大学)
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2009年10月 - 2010年3月応用物理学講義 (中央大学)
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2009年4月 - 2009年9月宇宙物理学講義 (中央大学)
共同研究・競争的資金等の研究課題
11-
日本学術振興会 科学研究費助成事業 2023年4月 - 2027年3月
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日本学術振興会 科学研究費助成事業 基盤研究(B) 2022年4月 - 2025年3月
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日本学術振興会 科学研究費助成事業 基盤研究(A) 2020年4月 - 2023年3月
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日本学術振興会 科学研究費助成事業 挑戦的研究(萌芽) 2019年6月 - 2022年3月
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日本学術振興会 科学研究費助成事業 新学術領域研究(研究領域提案型) 2013年4月 - 2015年3月
