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 教授
- J-GLOBAL ID
- 201801002962836691
- researchmap会員ID
- B000323419
- 外部リンク
主にX線天文学の研究をやっています。X線天体のフォローアップとして、地上赤外線観測、電波観測もやってます。ブラックホール、中性子星、白色矮星、AGN、銀河面からのX線放射などに興味を持っています。
宇宙航空研究開発機構（JAXA）・宇宙科学研究所（ISAS）にて、MAXI、XRISMを始めとする天文衛星のデータ処理・解析システムの開発、宇宙科学データアーカイブDARTSの運用を行っています。DARTSにおける全天多波長早見システムJUDO2を開発しました。また、「あかり」のアーカイブデータを用いて銀河系内の赤外線前景放射を見積もり、将来のLiteBIRDによる宇宙論観測に生かせるようにしたいと考えています。
東京大学大学院理学系研究科天文学専攻の教員です。
研究キーワード
2研究分野
1経歴
4-
2005年8月 - 現在
-
2001年8月 - 2004年12月
-
1991年4月 - 1992年3月
学歴
2-
1986年4月 - 1991年3月
-
1980年4月 - 1986年3月
委員歴
4-
2020年11月 - 現在
-
2020年4月 - 現在
-
2020年4月 - 現在
-
2020年4月 - 現在
論文
244-
Journal of Physics: Conference Series 632(1) 2015年8月13日 査読有り© Published under licence by IOP Publishing Ltd. The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF).
-
EPJ Web of Conferences 95 2015年5月29日 査読有り© Owned by the authors, published by EDP Sciences, 2015. The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF).
-
GEOPHYSICAL RESEARCH LETTERS 42(9) 3576-3582 2015年5月 査読有りThe Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) successfully observed vertical distributions of ozone (O-3) concentration in the middle atmosphere during the annular solar eclipse that occurred on 15 January 2010. In the mesosphere, where the photochemical lifetime of O-3 is relatively short (approximately 100s), altitude-dependent changes in O-3 concentration under reduced solar radiation and their temporal variations were clearly observed as a function of the eclipse obscuration. This study reports the vertical distributions of mesospheric O-3 during a solar eclipse event and analyzes theoretically the eclipse-induced changes. We show that simple analytical expressions for O-3 concentration, which assume that O-3 and O are in a photochemically steady state, can be used to describe the O-3 concentration under reduced solar radiation. The SMILES data obtained during the eclipse provide a unique opportunity to test our current understanding of mesospheric O-3 photochemistry.
-
ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS: XXIV 495 3-6 2015年 査読有りIn this paper we introduce two independent projects in progress in Japan. Dagik Earth is a visualization project of the Earth and planets on a spherical screen using only a standard PC and a projector. Surface images of the Earth or planets (or whatever having spherical shape) in the equirectangular (plate carre) projection are projected on a spherical screen in the orthographic projection. As a result, the spherical screen becomes a virtual digital globe, which can be rotated using mouse or remote controller. Inter-university Upper atmosphere Global Observation NETwork (IUGONET) is a collaboration of five Japanese institutes to build a comprehensive database system for the metadata of the upper-atmospheric data taken by these institutes. We explain the IUGONET metadata database and iUgonet Data Analysis Software (UDAS) for upper atmospheric research.
-
ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS: XXIV 495 499-502 2015年 査読有りThe Monitor of All-sky X-ray Image (MAXI) was launched on July 2009. It was equipped on the exposed facility of the Japanese experiment module "Kibo" on-board the international space station (ISS). The main purpose of the MAXI is to discover and promptly report X-ray transients as well as steady monitoring of known X-ray sources in the whole sky. The MAXI operation is approved at least until the end of March 2015. We are working on public data release of the MAXI, in order to enhance use of the MAXI data by scientists all over the world. On-demand data analysis system using a web-interface has started since November 2011. Now we are working toward permanent public MAXI data archive including MAXI specific software for scientific analysis.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 66(6) 2014年12月 査読有りThe narrow-line Seyfert 1 galaxy 1H 0707-495 is known to exhibit significant X-ray spectral variations. Its X-ray energy spectrum is characterized by a strong soft excess emission, an extremely deep iron K-edge structure at similar to 7 keV, and a putative iron L-line/edge feature at similar to 1 keV. We have found that the energy spectrum of 1H 0707-495 in 0.5-10 keV is successfully explained by a "variable double partial covering model" where the original continuum spectrum, which is composed of a soft multi-color disk blackbody component and a hard power-law component, is partially covered by two ionized absorption layers with different ionization states and the same partial covering fraction. The lower-ionized and thicker absorption layer primarily explains the iron K-edge feature, and the higher-ionized and thinner absorption layer explains the L-edge feature. We have discovered that the observed significant intensity/spectral variation within similar to 1 d is mostly explained by varying only the partial covering fraction. In our model, the intrinsic luminosity and spectral shape are hardly variable within similar to 1 d, while some intrinsic variability above 3 keV is recognized. This is consistent with the picture that the multi-color disk blackbody spectrum is almost invariable on this timescale, and the hard power-law component is more variable. We propose that the observed spectral variation of 1H 0707-495 is caused by three physically independent variations with different timescales; (1) intrinsic luminosity variation over days, (2) variation of partial covering fraction on a timescale of hours, and (3) small intrinsic hard component variation above 3 keV on a timescale of hours or less.
-
Nuclear Physics B - Proceedings Supplements 256-257 225-232 2014年12月1日 査読有り© 2014 Elsevier B.V. The CALorimetric Electron Telescope (CALET) space experiment, currently under development by Japan in collaboration with Italy and the United States, will measure the flux of cosmic-ray electrons (including positrons) to 20 TeV, gamma rays to 10 TeV and nuclei with Z=1 to 40 up to 1,000 TeV during a two-year mission on the International Space Station (ISS), extendable to five years. These measurements are essential to search for dark matter signatures, investigate the mechanism of cosmic-ray acceleration and propagation in the Galaxy and discover possible astrophysical sources of high-energy electrons nearby the Earth. The instrument consists of two layers of segmented plastic scintillators for the cosmic-ray charge identification (CHD), a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter (IMC) and a 27 radiation length thick lead-tungstate calorimeter (TASC). CALET has sufficient depth, imaging capabilities and excellent energy resolution to allow for a clear separation between hadrons and electrons and between charged particles and gamma rays. The instrument will be launched to the ISS within 2014 Japanese Fiscal Year (by the end of March 2015) and installed on the Japanese Experiment Module-Exposed Facility (JEM-EF). In this paper, we will review the status and main science goals of the mission and describe the instrument configuration and performance.
-
ASTROPHYSICAL JOURNAL LETTERS 784(2) 2014年4月 査読有りWe re-examine archival Ginga data for the black hole binary system GS 1124-683, obtained when the system was undergoing its 1991 outburst. Our analysis estimates the dimensionless spin parameter a(*) = cJ/GM(2) by fitting the X-ray continuum spectra obtained while the system was in the "thermal dominant" state. For likely values of mass and distance, we find the spin to be a(*) = -0.25(-0.64)(+0.05) (90% confidence), implying that the disk is retrograde (i.e., rotating antiparallel to the spin axis of the black hole). We note that this measurement would be better constrained if the distance to the binary and the mass of the black hole were more accurately determined. This result is unaffected by the model used to fit the hard component of the spectrum. In order to be able to recover a prograde spin, the mass of the black hole would need to be at least 15.25 M-circle dot, or the distance would need to be less than 4.5 kpc, both of which disagree with previous determinations of the black hole mass and distance. If we allow f(col) to be free, we obtain no useful spin constraint. We discuss our results in the context of recent spin measurements and implications for jet production.
-
SPACE TELESCOPES AND INSTRUMENTATION 2014: ULTRAVIOLET TO GAMMA RAY 9144 2014年 査読有りWF-MAXI is a soft X-ray transient monitor proposed for the ISS/JEM. Unlike MAXI, it will always cover a large field of view (20 % of the entire sky) to detect short transients more efficiently. In addition to the various transient sources seen by MAXI, we hope to localize X-ray counterparts of gravitational wave events, expected to be directly detected by Advanced-LIGO, Virgo and KAGRA in late 2010's. The main instrument, the Soft X-ray Large Solid Angle Cameras (SLC) is sensitive in the 0.7-12 keV band with a localization accuracy of similar to 0.1 degrees. The Hard X-ray Monitor (HXM) covers the same sky field in the 20 keV-1 MeV band.
-
SPACE TELESCOPES AND INSTRUMENTATION 2014: ULTRAVIOLET TO GAMMA RAY 9144 2014年 査読有りThe joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of Delta E <= 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.
-
Frascati Workshop 2013 - 10th International Workshop on Multifrequency Behaviour of High Energy Cosmic Sources 222-226 2014年 査読有りWe present the results of X-ray and Near-Infrared observations of the Galactic Ridge X-ray Emission (GRXE). We extracted 2,002 X-ray point sources in the Chandra Bulge Field (l =0?.113, b = 1?.424) down to ∼10-14.8 ergs cm-2 s-1 in 2-8 keV band with the longest observation (∼900 ks) of the GRXE. Based on X-ray brightness and hardness, we classified the X-ray point sources into three groups: A (hard), B (soft and broad spectrum), and C (soft and peaked spectrum). In order to know populations of the X-ray point sources, we carried out NIR imaging and spectroscopy observation. We identified ∼11% of X-ray point sources with NIR and extracted NIR spectra for some of them. Based on X-ray and NIR properties, we concluded that non-thermal sources in the group A are mostly active galactic nuclei and the thermal sources are mostly white dwarf binaries such as cataclysmic variables (CVs) and Pre-CVs. We concluded that the group B and C sources are X-ray active stars in flare and quiescence, respectively.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 65(2) 2013年4月 査読有りDuring a routine calibration observation of 1E 0102.2-7219 in the Small Magellanic Cloud (SMC), carried out in 2012 October for the Suzaku satellite, we detected a transient X-ray source at (RA, Dec) = (01(h)02(m)47(s), -72 degrees 04(m)54(s)) in the equinox J2000.0 with a positional uncertainty of similar to 1.'' 4. We conducted a temporal and spectral analysis of the source and found a coherent pulse signal with a period of 522.3 +/- 0.1 s. We also found a featureless spectrum described by a single power-law model with a photon index of 1.0(-0.1)(+0.1) and a 0.5-10 keV luminosity of similar to 8.8 x 10(35) ergs s(-1) at an assumed distance of 60 kpc. The Suzaku source is likely to be the counterpart of 2XMM J010247.4-720449, which has been observed several times, including outburst detected by Swift. Based on the X-ray characteristics from our data, as well as the transient record and optical and near-infrared features described in the literature, we conclude that this source is a high-mass X-ray binary pulsar with a Be star companion in the SMC, which is known to harbor an exceptionally large (80) number of such sources compared to that in our Galaxy.
-
ASTROPHYSICAL JOURNAL 766(1) 2013年3月 査読有りApparently diffuse X-ray emission has been known to exist along the central quarter of the Galactic Plane since the beginning of X-ray astronomy; this is referred to as the Galactic Ridge X-ray emission (GRXE). Recent deep X-ray observations have shown that numerous X-ray point sources account for a large fraction of the GRXE in the hard band (2-8 keV). However, the nature of these sources is poorly understood. Using the deepest X-ray observations made in the Chandra bulge field, we present the result of a coherent photometric and spectroscopic analysis of individual X-ray point sources for the purpose of constraining their nature and deriving their fractional contributions to the hard-band continuum and Fe K line emission of the GRXE. Based on the X-ray color-color diagram, we divided the point sources into three groups: A (hard), B (soft and broad spectrum), and C (soft and peaked spectrum). The group A sources are further decomposed spectrally into thermal and non-thermal sources with different fractions in different flux ranges. From their X-ray properties, we speculate that the group A non-thermal sources are mostly active galactic nuclei and the thermal sources are mostly white dwarf (WD) binaries such as magnetic and non-magnetic cataclysmic variables (CVs), pre-CVs, and symbiotic stars, whereas the group B and C sources are X-ray active stars in flares and quiescence, respectively. In the logN-log S curve of the 2-8 keV band, the group A non-thermal sources are dominant above approximate to 10(-14) erg cm(-2) s(-1), which is gradually taken over by Galactic sources in the fainter flux ranges. The Fe K alpha emission is mostly from the group A thermal (WD binaries) and the group B (X-ray active stars) sources.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(6) 2012年12月 査読有りWe propose a simple spectral model for the Seyfert 1 Galaxy MCG -6-30-15 that can explain most of the 1-40 keV spectral variation by a change of the partial covering fraction, similar to that proposed by Miller, Turner, and Reeves (2008, A&A, 483, 437). Our spectral model is composed of three continuum components: (1) a direct power-law component, (2) a heavily absorbed power-law component by mildly ionized intervening matter, and (3) a cold-disk reflection component far from the black hole with a moderate solid-angle (Omega/2 pi similar or equal to 0.3) accompanying a narrow fluorescent iron line. The first two components are affected by the surrounding thin highly ionized absorber with N-H similar or equal to 10(23.4) cm(-2) and log xi similar or equal to 3.4. The heavy absorber in the second component is fragmented into many clouds, each of which is composed of radial zones with different ionization states and different column densities, a main body (N-H similar or equal to 10(24.2) cm(-2), log xi similar or equal to 1.6), an envelope (N-H similar or equal to 10(22.1) cm(-2), log xi similar or equal to 1.9), and presumably a completely opaque core. Not only the intrinsic spectral shape of the X-ray source but also these parameters of the ionized absorbers are unchanged at all. The central X-ray source extends moderately, and its luminosity is not significantly variable. The observed flux and spectral variations are mostly explained by the variation of the geometrical partial covering fraction of the central source ranging from 0 (uncovered) to similar to 0.63 by the intervening ionized clouds in the line of sight. The ionized iron K-edge of the heavily absorbed component explains most of the seemingly broad line-like features, a well-known spectral characteristic of MCG -6-30-15. The direct component and the absorbed one are negatively correlated, and their variations cancel out each other, so that the fractional spectral variation becomes the minimum at the iron-energy band; thus, another observational characteristic of MCG -6-30-15 is explained.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(4) 2012年8月 査読有りWe present the result of a Suzaku X-ray spectroscopic observation of the dwarf nova Z Cam, which was conducted by chance at the onset of an optical outburst. We used the X-ray Imaging Spectrometer (a 38 ks exposure) and the Hard X-ray Detector (34 ks) to obtain a 0.35-40 keV spectrum simultaneously. Spectral characteristics suggest that the source was in the X-ray quiescent state, despite being in the rising phase of an outburst in the optical band. The spectrum shows a clear signature of circumstellar absorption in excess of interstellar absorption and the reprocessed-emission features of Fe fluorescence and Compton scattering. The extra absorption is explained as being due to partial covering by either neutral or ionized matter. We found a spectral change during the observation, which is attributable only to a change in the circumstellar absorption. Such an X-ray spectral variation was reported for the first time in the case of dwarf novae. We speculate that the variation in the circumstellar absorption is interpreted as a time-varying disk wind, or geometrically flaring disk around the white dwarf during the propagation of a heat wave along inward the accretion disk at the beginning of the outburst, in which optical outburst and X-ray quiescent states co-exist.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(1) 2012年2月 査読有りWe report on an X-ray spectral analysis of the black hole candidate XTE J1752-223 in the 2009-2010 outburst, utilizing data obtained with the MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work complementarily. As already reported by Nakahira et al. (2010, PASJ, 62, L27), MAXI monitored the source continuously throughout the entire outburst for about eight months. All of the MAXI/GSC energy spectra in the high/soft state, lasting for 2 months, are well represented by a multi-color disk plus power-law model. The innermost disk temperature changed from similar to 0.7 keV to similar to 0.4 keV and the disk flux decreased by an order of magnitude. Nevertheless, the innermost radius is constant at similar to 41 D-3.5(cos i)(-1/2) km, where D-3.5 is the source distance in units of 3.5 kpc and i the inclination. The multi-color disk parameters obtained with the MAXI/GSC are consistent with those with the Swift/XRT and Suzaku. The Suzaku data also suggest a possibility that the disk emission is slightly Comptonized, which could account for broad iron-K features reported previously. Assuming that the obtained innermost radius represents the innermost stable circular orbit for a non-rotating black hole, we estimate the mass of the black hole to be 5.51 +/- 0.28 M-circle dot D-3.5(cos i)(-1/2), where the correction for the stress-free inner boundary condition and color hardening factor of 1.7 are taken into account. If the inclination is less than 49 degrees, as suggested from radio monitoring of transient jets, and the soft-to-hard transition in 2010 April occurred at 1%-4% of Eddignton luminosity, the fitting of the Suzaku spectra with a relativistic accretion-disk model derives constraints on the mass and the distance to be 3.1-55 M-circle dot and 2.3-22 kpc, respectively. This confirms that the compact object in XTE J1752-223 is a black hole.
-
SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りFermi is discovering many new gamma-ray sources, and 1FGL J1227.9-4852 is one of them. Recent studies suggest that this source is associated with the X-ray source XSS J12270-4859 (here-after J12270), of which nature is poorly understood. In this paper, we show results of our Suzaku and RXTE X-ray observations which are partly simultaneous with near-infrared (NIR) observations using InfraRed Survey Facility (IRSF). We found that J12270 shows (1) no emission lines in the X-ray spectra, (2) unique rapid temporal variations in X-rays, and (3) almost simultaneous X-ray and NIR flares. To investigate its nature, we constructed a spectral energy distribution (SED) from radio to gamma-rays. Because of the similarity of its SED with those of other microquasars, we propose that J12270 is a microquasar with a synchrotron jet, and also the first gamma-ray emitting low-mass X-ray binary.
-
SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りWe carried out a Suzaku observation for 100 ksec on the Chandra deep observation region (1, b) approximate to (0.degrees 08, -1.degrees 42), and also reanalyzed the Chandra archival data. We found the Suzaku and Chandra GRXE absolute fluxes are consistent, and it is about twice of the Chandra total point source flux above 6 keV. We resolved the Fe K-complex component into the neutral or low-ionized (6.40 keV), He-like (6.67 keV) and H-like (6.97 keV) lines, and studied latitudinal dependence of the Fe line intensity, using multiple Suzaku pointings perpendicular to the Galactic plane. Consequently, we found not only Fe line fluxes but also their equivalent widths significantly decrease with Galactic latitudes. Our results are difficult to be reconciled with the point source model, but may be explained if there is some excess diffuse component of the GRXE accompaning hardly Fe line emission and has a larger Galactic scale height than that of the point sources.
-
GALACTIC ARCHAEOLOGY: NEAR-FIELD COSMOLOGY AND THE FORMATION OF THE MILKY WAY 458 233-234 2012年 査読有りThe Galactic Ridge X-ray Emission (GRXE) is an apparently extended emission along the Galactic Plane. Its origin has been a mystery for a long time. However, recent study revealed that about 80% of the GRXE is consist of dim X-ray point sources. It raises a new question, what are the populations of them? In this study, we identified X-ray point sources constituting the GRXE with near-infrared (NIR) and obtained NIR spectra. The spectra suggest that almost the sources are late-type stars.
-
DEATH OF MASSIVE STARS: SUPERNOVAE AND GAMMA-RAY BURSTS (279) 329-330 2012年 査読有りThe Galactic Ridge X-ray Emission (GRXE) spectrum has strong iron emission lines at 6.4, 6.7, and 7.0 keV, each corresponding to the neutral (or low-ionized), He-like, and H-like iron ions. The 6.4 keV fluorescence line is due to irradiation of neutral (or low ionized) material (iron) by hard X-ray sources, indicating uniform presence of the cold matter in the Galactic plane. In order to resolve origin of the cold fluorescent matter, we examined the contribution of the 6.4 keV line emission from white dwarf surfaces in the hard X-ray emitting symbiotic stars (hSSs) and magnetic cataclysmic variables (mCVs) to the GRXE. In our spectral analysis of 4 hSSs and 19 mCVs observed with Suzaku, we were able to resolve the three iron emission lines. We found that the equivalent-widths (EWs) of the 6.4 keV lines of hSSs are systematically higher than those of mCVs, such that the average EWs of hSSs and mCVs are.180(-10)(+50)eV and 93(-3)(+20) eV, respectively. The EW of hSSs compares favorably with the typical EWs of the 6.4 keV line in the GRXE of 90-300 eV depending on Galactic positions. Average 6.4 keV line luminosities of the hSSs and mCVs are 9.2 x 10(39) and 1.6 x 10(39) photons s(-1), respectively, indicating that hSSs are intrinsically more efficient 6.4 keV line emitters than mCVs. We estimated required space densities of hSSs and mCVs to account for all the GRXE 6.4 keV line emission flux to be 2 x 10(-7) pc(-3)and 1 x 10(-6) pc (-3), respectively. We also estimated the actual 6.4 keV line contribution from the hSSs, which is as much as 30% of the observed GRXE flux, and that from the mCV is about 50%. We therefore conclude that the GRXE 6.4 keV line flux is primarily explained by hSSs and mCVs.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S669-S675 2011年11月 査読有りA new X-ray spectro-temporal data-analysis method, which we call "the difference variation function method", is introduced. It can analyze spectral and temporal variations of X-ray sources, and its merits are discussed in comparison with conventional data-analysis methods. The new method is being applied to Suzaku observation data of the Seyfert 1 galaxy MCG -6-30-15. Consequently, it has been found that the observed spectral and temporal variations on a time scale of approximate to 10-100 ks are mostly ascribed to variable partially absorbers in front of the central X-ray source, whereas the X-ray source is intrinsically variable mainly on time scales shorter than approximate to 10 ks.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S759-S769 2011年11月 査読有りXSS J12270-4859 (J12270) is an enigmatic source of unknown nature. Previous studies revealed that the source has unusual X-ray temporal characteristics, including repetitive short-term flares, followed by spectral hardening, non-periodic dips, and dichotomy in activity; i.e., intervals filled with flares and those without. Together with a power-law X-ray spectrum, it is suggested to be a low-mass X-ray binary. In order to better understand the object, we present the results of our near-infrared (NIR) photometry and linear polarimetry observations as well as X-ray spectroscopy observations, which overlap with each other partially in time, taken respectively with the InfraRed Survey Facility (IRSF) and the Rossi X-ray Tinting Explorer (RXTE). We detected several simultaneous NIR and X-ray flares for the first time. No significant NIR polarization was obtained. We assembled data taken with IRSF, RXTE, Suzaku, Swift, and other missions in the literature and compared the flare profile and the spectral energy distribution (SED) with some representative high-energy sources. Based on some similarities of the repetitive NIR and X-ray flaring characteristics and the broad SED, we argue that J12270 is reminiscent of microquasars with a synchrotron jet, which is at a very low-luminosity state of approximate to 10(-4) Eddington luminosity for a stellar mass black hole or neutron star at a reference distance of 1 kpc.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(SPEC. ISSUE 3) S713-S716 2011年11月 査読有りWe present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of 3 x 10(-9) erg cm(-2)s(-1) in 2-20 keV band during the scan transit starting at 2010-09-07 18:24:30 (UT). The estimated X-ray luminosity at the scan in the energy band is 3 x 10(32) erg s(-1), indicating that the event is among the largest X-ray flares from T Tauri stars. Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, log L-X/L-bol = -0.1(-0.3)(+0.2); i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(SPEC. ISSUE 3) S821-S825 2011年11月 査読有りWe report on the MAXI GSC X-ray monitoring of the Crab nebula and pulsar during the GeV gamma-ray flare for the period of 2010 September 18-24 (MJD 55457-55463), detected by AGILE and Fermi-LAT. There were no significant variations on the pulse phase averaged and pulsed fluxes during the gamma-ray flare on time scales from 0.5 to 5 days. The pulse profile also showed no significant change during this period. The upper limits on the variations of the pulse phase averaged and pulsed fluxes for the period MJD 55457.5-55462.5 in the 4-10 keV band were derived to be 1% and 19%, respectively, at the 90% confidence limit of the statistical uncertainty. The lack of variations in the pulsed component over the multi-wavelength range (radio, X-ray, hard X-ray, and gamma-ray) supports not a pulsar, but a nebular origin for the gamma-ray flare.
-
ASTROPHYSICAL JOURNAL 722(1) 760-773 2010年10月 査読有りVariable ultraluminous X-ray sources (ULXs), which are considered to be black hole binaries (BHBs), are known to show state transitions similar to Galactic BHBs. However, the relation between the ULX states and the Galactic BHB states is still unclear, primarily due to the less well-understood behaviors of ULXs in contrast to the Galactic BHBs. Here, we report a statistical X-ray spectral study of 34 energy spectra from seven bright ULXs in the interacting galaxy systems M 51 and NGC 4490/85, using archive data from multiple Chandra and XMM-Newton observations spanning a few years. In order to compare them with Galactic BHB states, we applied representative spectral models of BHBs-a power-law (PL), a multi-color disk blackbody (MCD), and a slim-disk model-to all the ULX spectra. We found a hint of a bimodal structure in the luminosity distribution of the samples, suggesting that ULXs have two states that respectively have typical luminosities of (3-6) x 10(39) and (1.5-3) x 10(39) ergs s(-1). Most spectra in the brighter state are explained by the MCD or the slim-disk model, whereas those in the fainter state are explained by the PL model. In particular, the slim-disk model successfully explains the observed spectral variations of NGC 4490/85 ULX-6 and ULX-8 by changes of the mass accretion rate to a black hole of an estimated mass of <40 M-circle dot. From the best-fit model parameters of each state, we speculate that the brighter state in these two ULXs corresponds to the brightest state of Galactic BHBs, which is often called the "apparently standard state." The fainter state of the ULXs has a PL-shaped spectrum, but the photon index range is much wider than that seen in any single state of Galactic BHBs. We thus speculate that it is a state unique to ULXs. Some sources show much fainter and steeper spectra than the faint state, which we identified as yet another state.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(5) L27-L32 2010年10月 査読有りWe present the first results on the black-hole candidate XTE J1752-223 from the Gas Slit Camera (GSC) aboard the Monitor of All-sky X-ray Image (MAXI) on the International Space Station. Including the onset of an outburst reported by the Proportional Counter Array aboard the Rossi X-ray Timing Explorer on 2009 October 23, MAXI / GSC has been monitoring this source approximately 10 times per day with high sensitivity in the 2-20 keV band. XTE J1752-223 was initially in a low/hard state during the first 3 months. An anti-correlated behavior between the 2-4 keV and 4-20 keV bands was observed around 2010 January 20, indicating that the source exhibited a spectral transition to the high / soft state. A transient radio jet may have been ejected when the source was in the intermediate state where the spectrum was roughly explained by a power-law with a photon index of 2.5-3.0. The unusually long period in the initial low/hard state implies a slow variation in the mass-accretion rate, and a dramatic soft X-ray increase may be explained by a sudden appearance of the accretion disk component with a relatively low innermost temperature (0.4-0.7 keV). Such a low temperature might suggest that the maximum accretion rate was just above the critical gas-evaporation rate required for the state transition.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(5) 1185-1189 2010年10月 査読有りWe have applied the light-bending model of X-ray variability to Suzaku data of the Seyfert 1 galaxy MCG -6-30-15. We analyzed the energy dependence of the root mean square variability, and discussed conditions necessary for the model to explain the characteristic decrease of the source variability at around 5-8 keV. A model, where the X-ray source moves radially rather than vertically close to the disk surface, can indeed reproduce the reduced variability near the energy of the Fe K alpha line, although the formal fit quality is poor. The model then predicts the energy spectra, which can be compared to observational data. The spectra are strongly reflection dominated, and do not provide a good fit to Suzaku spectral data of the source. The inconsistency of this result with some previous claims can be traced to our using data in a broader energy band, where the effects of a warm absorber in the spectrum cannot be neglected.
-
ASTROPHYSICAL JOURNAL LETTERS 719(2) L116-L120 2010年8月 査読有りDuring the search for counterparts of very high energy gamma-ray sources, we screndipitously discovered large, extended, low surface brightness emission from pulsar wind nebulae (PWNe) around pulsars with the ages up to similar to 100 kyr, a discovery made possible by the low and stable background of the Suzaku X-ray satellite. A systematic study of a sample of eight of these PWNe, together with Chandra data sets, has revealed that the nebulae keep expanding up to similar to 100 kyr, although the timescale of the synchrotron X-ray emission is only similar to 60 yr for typical magnetic fields of 100 mu G. Our result suggests that the accelerated electrons up to similar to 80 TeV can escape from the PWNe without losing most energies. Moreover, in order to explain the observed correlation between the X-ray size and the pulsar spin-down age, the magnetic field strength in the PWNe must decrease with time.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(4) 981-986 2010年8月 査読有りWe report on the detection of a time variable O VII line emission in a deep 100 ks Suzaku X-ray Imaging Spectrometer spectrum of the galactic ridge X-ray emission. The observed line intensity is too strong (11 +/- 2 line unit or photon cm(-2) s(-1) sr(-1)) to be emitted inside the heavily obscured galactic disk. It showed a factor of two time variation that showed a significant (similar to 4 sigma) correlation with the solar-wind O7+ ion flux. The high line intensity and good time correlation with the solar wind strongly suggests that it originated from geocoronal solar-wind charge-exchange emission. We discuss the X-ray line intensity while considering a line-of-sight direction and also theoretical distribution models of the neutral hydrogen and solar wind around Earth. Our results indicate that X-ray observations of geocoronal solar-wind charge-exchange emission can be used to constrain these models.
-
Astrophysical Journal 713(1) 257-268 2010年4月10日 査読有りWe present results from the Suzaku observation of the microquasar GRS 1915+105 performed during the 2005 October multiwavelength campaign. The data include both stable state (class chi) and limit-cycle oscillation (class theta). Correct interstellar absorption as well as effects of dust scattering are fully taken into account in the spectral analysis. The energy spectra in the 2-120 keV band in both states are all dominated by strong Comptonization of disk photons by optically thick (tau approximate to 7-10) and low-temperature (T-e approximate to 2-3 keV) hybrid plasmas containing non-thermal electrons produced with 10%-60% of the total power input. Absorption lines of highly ionized Fe ions detected during the oscillation indicate that a strong disk wind is developed. The ionization stage of the wind correlates with the X-ray flux, supporting the photoionization origin. The iron-K emission line shows a strong variability during the oscillation; the reflection is strongest during the dip but disappears during the flare. We interpret this as evidence for self-shielding" that the Comptonizing corona becomes geometrically thick in the flare phase, preventing photons from irradia
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(1) 179-186 2010年2月 査読有りSuzaku observed the region including HESS J1809-193, a TeV unidentified source, and confirmed the existence of extended hard X-ray emission previously reported by ASCA, as well as hard X-ray emission from PSR J1809-1917 in this region. A one-dimensional profile of the diffuse emission is represented along with a Gaussian model with a best-fit sigma of 7' +/- 1'. The diffuse emission extends for at least 21 pc (at the 3 sigma level, assuming a distance of 3.5 kpc), and has a hard spectrum with a photon index of Gamma similar to 1.7. The hard spectrum suggests a pulsar wind nebula origin, which is also strengthened by the hard X-ray emission from PSR J1809-1917, itself. Thanks to the low background of Suzaku XIS, we were able to investigate the spatial variation of the energy spectrum, but no systematic spectral change in the extended emission was found. These results imply that the X-ray emitting pulsar wind electrons can travel up to 21 pc from the pulsar without any noticeable energy loss via synchrotron emission.
-
Astronomische Nachrichten 331(2) 152-155 2010年2月 査読有りWe present X-ray spectral analysis of the super-soft source CAL87 using ASCA, Chandra, XMM-Newton observations. Early ASCA CCD spectrum reported a strong oxygen absorption edge, which is considered to originate in the an optically thick white-dwarf atmosphere. On the other hand, contemporaneous grating observations by Chandra and XMM-Newton indicate emission line dominated spectra, which obviously indicate the optically thin origin. Fitting all the available CCD (ASCA and XMM-Newton) and grating spectra (XMM-Newton and Chandra) simultaneously, we show that the CAL87 X-ray energy spectrum is in fact composed of both an optically thick component with deep absorption edges and an optically thin component with numerous emission lines. The current result supports the standard SSS model that the primary source of X-ray emission is nuclear burning in the white dwarf atmosphere, surrounded by a highly photoionised, optically thin corona. © 2010 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim.
-
SPACE TELESCOPES AND INSTRUMENTATION 2010: ULTRAVIOLET TO GAMMA RAY 7732 2010年 査読有りThe joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray detector (40-600 keV). The micro-calorimeter system is developed by an international collaboration led by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of Delta E similar to 7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be pursued.
-
X-RAY ASTRONOMY-2009: PRESENT STATUS, MULTI-WAVELENGTH APPROACH AND FUTURE PERSPECTIVES, PROCEEDINGS 1248 317-+ 2010年 査読有りSuzaku has enabled us to study wide-band spectral and timing properties of black-hole binaries and AGNs more accurately than ever, and revealed how the continuum definition can affect Fe-K line profiles. We have reproduced 0.5-300 keV spectra of Cyg X-1 and GRO J1655-40 in terms of thermal Comptonization in highly inhomogeneous coronae. In both objects, R-in was constrained by the Fe-K line profile and soft excess as similar to 10 R-g, as opposed to the relativistic Fe-K line reported in the literature. We also re-analyzed the 0.7-300 keV Suzaku spectra of OX 339-4, and found that a careful modeling of the continuum leads to R-in > R-g(Yamada et al. 2009), again in disagreement with Miller et al. (2008). Furthermore, through a systematic analysis of AGNs, we discovered a hard spectral component in the HXD-PIN band, which varies independently of the powerlaw. Taking this into account, the time-averaged spectra of MCG-6-30-15 have been explained by invoking neither a large refection fraction, nor an extreme broad Fe-K line. The essence here is that the hard X-ray (20-40 keV) bump may be partially explained as an additional Comptonization component. Our results indicate that the extremely relativistic Fe-K line reported for some objects is not a unique solution, and depends in many cases on the continuum modeling.
-
AIP Conference Proceedings 1248 531-536 2010年 査読有りMAXI, the first astronomical payload attached to ISS JEM-EF, began operation on August 3, 2009 for monitoring all-sky X-ray images every ISS orbit (92 min). This paper reports the first results obtained during the 1-month test observations. All instruments as well as two main X-ray slit cameras, the GSC and SSC, worked as we expected. The detection limits of MAXI-GSC are about 25 mCrab and 8 mCrab for one ISS orbit (92 min) and 1-day observations, respectively. GSC covers about 76% and 96% of the entire sky for respective single-orbit and 1-day observations. MAXI has detected a transient X-ray pulsar A0535+26, an X-ray burst, and a gamma-ray burst in the first month of the test observation period. © 2010 American Institute of Physics.
-
Astrophysical Journal 707(2 PART 2) L109-L113 2009年12月20日 査読有りThe wide-band Suzaku spectra of the black hole (BH) binary GX 339-4, acquired in 2007 February during the Very High state, were reanalyzed. Effects of event pileup (significant within similar to 3' of the image center) and telemetry saturation of the X-ray Imaging Spectrometer (XIS) data were carefully considered. The source was detected up to similar to 300 keV, with an unabsorbed 0.5-200 keV luminosity of 3.8 x 10(38) erg s(-1) at 8 kpc. The spectrum can be approximated by a power law of photon index 2.7, with a mild soft excess and a hard X-ray hump. When using the XIS data outside 2' of the image center, the Fe K line appeared extremely broad, suggesting a high BH spin as already reported by Miller et al. based on the same Suzaku data and other CCD data. When the XIS data accumulation is further limited to > 3' to avoid event pileup, the Fe K profile becomes narrower, and a marginally better solution appears which suggests that the inner disk radius is 5-14 times the gravitational radius (1 sigma), though a maximally spinning BH is still allowed by the data at the 90% confidence level. Consistently, the optically thick accretion disk is inferred to be truncated at a radius 5-32
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(6) 1355-1364 2009年12月 査読有りWe have investigated the spectral variation of the Seyfert 1 galaxy MCG-6-30-15 observed with Suzaku in 2006 January for three separate periods spreading over fourteen days. We found that the time-averaged continuum energy spectrum between 1 keV and 40 keV can be approximated with a spectral model composed of a direct power-law component, its reflection component, two warm absorbers with different ionization states, and neutral absorption. We have taken two approaches to study its spectral variation at various timescales. The first approach was to make intensity-sliced spectra, and to study any correlation between the intensity and the spectral shape. The second approach was to study spectral changes between the intervals when the source flux is above ("bright state") and below ("faint state") the average for fixed time-intervals. In both approaches, we found a clear correlation between the intensity in the 6-10keV band and the spectral ratio of 0.5-3.0keV/6.0-10keV. Such a spectral variation requires a change of the apparent slope of the direct component, whereas the shape and intensity of the reflection component are invariable. The observed apparent spectral change is explained by the variation of the ionization degree of one of the two warm absorbers due to the intrinsic source luminosity variation. The Current results suggest that the warm absorber has a critical role to explain the observed continuum spectral shape and the variation of MCG-6-30-15, which is essential to constrain the parameters of the putatively broadened iron line emission feature.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC 121(885) 1279-1290 2009年11月 査読有りWe present an empirical model of Comptonization for fitting the spectra of X-ray binaries. This model, named SIMPL, has been developed as a package implemented in XSPEC. With only two free parameters, SIMPL is competitive as the simplest model of Compton scattering. Unlike the pervasive standard power-law model, SIMPL incorporates the basic features of Compton scattering of soft photons by energetic coronal electrons. Using a simulated spectrum, we demonstrate that SIMPL closely matches the behavior of physical Comptonization models that consider the effects of optical depth, coronal electron temperature, and geometry. We present fits to RXTE spectra of the black hole transient H1743-322 and a BeppoSAX spectrum of LMC X-3 using both SIMPL and the standard power-law model. A comparison of the results shows that SIMPL gives equally good fits, while eliminating the troublesome divergence of the standard power-law model at low energies. SIMPL is completely flexible and can be used self-consistently with any seed spectrum of photons. We show an example of how SIMPL-unlike the standard power law-teamed up with DISKBB (the standard model of disk accretion) provides a uniform disk normalization that is unaffected by moderate Comptonization.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(5) 999-1010 2009年10月 査読有りThe Monitor of All-sky X-ray Image (MAXI) mission is the first astronomical payload to be installed on the Japanese Experiment Module - Exposed Facility (JEM-EF or Kibo-EF) on the International Space Station. It has two types of X-ray slit cameras with wide FOVs and two kinds of X-ray detectors consisting of gas proportional counters covering the energy range of 2 to 30keV and X-ray CCDs covering the energy range of 0.5 to 12keV. MAXI will be more powerful than any previous X-ray All Sky Monitor payloads, being able to monitor hundreds of Active Galactic Nuclei. A realistic simulation under optimal observation conditions suggests that MAXI will provide all-sky images of X-ray sources of similar to 20 mCrab (similar to 7 x 10(-10) erg cm(-2) s(-1) in the energy band of 2-30 keV) from observations during one ISS orbit (90 min), similar to 4.5 mCrab for one day, and similar to 2 mCrab for one week. The final detectability of MAXI could be similar to 0.2 mCrab for two years, which is comparable to the source confusion limit of the MAXI field of view (FOV). The MAXI objectives are: (1) to alert the community to X-ray novae and transient X-ray sources, (2) to monitor long-term variabilities of X-ray sources, (3) to stimulate multi-wavelength observations of variable objects, (4) to create unbiased X-ray source cataloges, and (5) to observe diffuse cosmic X-ray emissions, especially with better energy resolution for soft X-rays down to 0.5 keV.
-
ASTROPHYSICAL JOURNAL 701(2) 1076-1090 2009年8月 査読有りThe first extragalactic X-ray binary, LMC X-1, was discovered in 1969. In the 1980s, its compact primary was established as the fourth dynamical black hole candidate. Recently, we published accurate values for the mass of the black hole and the orbital inclination angle of the binary system. Building on these results, we have analyzed 53 X-ray spectra obtained by RXTE and, using a selected sample of 18 of these spectra, we have determined the dimensionless spin parameter of the black hole to be a(*) = 0.92(-0.07)(+0.05). This result takes into account all sources of observational and model-parameter uncertainties. The standard deviation around the mean value of a(*) for these 18 X-ray spectra, which were obtained over a span of several years, is only Delta a(*) = 0.02. When we consider our complete sample of 53 RXTE spectra, we find a somewhat higher value of the spin parameter and a larger standard deviation. Finally, we show that our results based on RXTE data are confirmed by our analyses of selected X-ray spectra obtained by the XMM-Newton, BeppoSAX, and Ginga missions.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(4) L13-L16 2009年8月 査読有りWe report on the results of a Suzaku X-ray observation of XSS J12270-4859, one of the hard X-ray sources in the INTEGRAL catalogue. This object has been classified as an intermediate polar (IP) by its optical spectra, and a putative X-ray period of similar to 860 s. With a 30 ks exposure by Suzaku, we obtained a well-exposed spectrum in the 0.2-70keV band. We conclude against a previous IP classification based on a lack of Fe K alpha emission features in the spectrum and a failure to confirm the previously reported X-ray period. Instead, the X-ray light curve is filled with exotic phenomena, including repetitive flares lasting for similar to 100 s, occasional dips with no apparent periodicities, spectral hardening after some flares, and bimodal changes pivoting between quiet and active phases. The rapid flux changes, the dips, and the power-law spectrum point toward an interpretation that this is a low-mass X-ray binary. Some temporal characteristics are similar to those in the Rapid Burster and GROJ1744-28, making XSS J12270-4859 a very rare object.
-
Fusion Engineering and Design 84(7-11) 1713-1715 2009年6月 査読有りEngineering analyses have been performed for the representative diagnostic upper port plug of ITER. Maintenance and integration design have been also carried out for the diagnostic components to be installed in the upper port plug. From the electromagnetic and structural analyses, it has come up an important problem to suppress the displacement of the upper port plug rather than to reduce the produced stress. Reducing the electro-magnetic (EM) force will help to decrease the severity of potential displacement. Maximum displacement of the port plug decreases with increase in the number of slits in a manner that the displacement would seem to be less than the design tolerance. A proposed low body roller and inner frame may enhance maintenance and integration. These studies and designs have established the design basis for the diagnostic upper port plug. © 2009 Elsevier B.V. All rights reserved.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S107-S113 2009年1月 査読有りThe broad-band 1-300 keV Suzaku spectrum of IGR J17497-2821, the X-ray transient discovered by INTEGRAL in 2006 September, is presented. Suzaku observed IGR J17497-2821 on September 25, eight days after its discovery, for a net exposure of about 53 ks. During the Suzaku observation, IGR J17497-2821 is very bright, 2 x 10(37) erg s(-1) at 8 kpc in the 1-300 keV range, and shows a hard spectrum, typical of black hole candidates in the low-hard state. Despite the multi-mission X-ray monitoring of the source, only with Suzaku is it possible to obtain a broad-band spectrum in the 1-300 keV range with a very high signal to noise ratio. A sum of a multi-color disc and a thermal Comptonization component with mild reflection is a good representation of our IGR J17497-2821 Suzaku spectrum. The spectral properties of the accretion disc as well as the cut-off energy in the spectrum at about 150 keV are clearly detected and constrained. We discuss the implications on the physical model used to interpret the data and the comparison with previous results.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S183-S187 2009年1月 査読有りWe present ASCA and Suzaku studies of the TeV source HESS J1837-069, which has not been identified in other wavelengths. We confirm the presence of two X-ray sources in the Suzaku XIS image, AX J1838.0-0655 and AX J1837.3-0652, near both ends of the elongated TeV emission region. The XIS spectra of the two sources were reproduced by an absorbed power-law model, whose parameters are all consistent with those determined by the ASCA data. Recently, 70.5 ms X-ray Pulsation has been detected with RXTE in the sky region including HESS J1837-069 (Gotthelf & Halpern 2008, ApJ, 681, 515). Using the ASCA GIS data, which has both timing and imaging capabilities, we identified the pulsation Source as AX J1838.0-0655. The pulse periods determined by ASCA and Suzaku, and that reported with RXTE indicate steady spin-down at 4.917(4) x 10(-14) s s(-1). These results suggest that AX J1838.0-0655 is an intrinsically stable source, and presumably a pulsar wind nebula (PWN). We discuss the possibility that AX J1838.0-0655 is associated with HESS J1837-069 and the VHE gamma-ray ernission is originated from the PWN.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S225-S232 2009年1月 査読有りIn order to elucidate the origin of galactic ridge X-ray emission, we analyzed Suzaku data taken at various regions along the galactic plane, and studied their Fe-K emission line features. Suzaku resolved the Fe line complex into three narrow lines at similar to 6.4 keV, similar to 6.7 keV and similar to 6.97 keV, which are K-lines from neutral (or low-ionized), He-like, and H-like iron respectively. The 6.7 keV line is clearly seen in all of the observed regions, and its longitudinal distribution is consistent with that determined from previous observations. The 6.4 keV emission line was also found in various galactic plane regions (b similar to 0 degrees). Differences in the flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines between the galactic plane and the galactic center regions were studied and its implication was discussed.
-
HIGH ENERGY GAMMA-RAY ASTRONOMY 1085 376-+ 2009年 査読有りRadio and X-ray observations towards the VHE gamma-ray source HESS J1813-178, initially dubbed as a "dark accelerator", suggested its association with the SNR G12.8-0.0. Subsequent XMM and Chandra observations confirmed earlier ASCA findings of an extended, center-filled X-ray source, not resembling the contours of the radio-detected supernova remnant (SNR). Morphological and spectral resemblance of the X-ray emission seen at the center of the shell of SNR G12.8-0.0 with a Pulsar Wind Nebula (PWN) suggest HESS J1813-178 is one of the increasing number of objects classified as "composite SNR". In March 2007, 65 ksec Suzaku observations were taken, and we are able to confirm the previously reported characteristics of the X-ray counterpart from HESS J1813-178 as a diffuse hard X-ray source central to the radio-shell of SNR G12.8-0.0.
-
Proceedings of Science 2009年 査読有りMonitor of All Sky X-ray Image (MAXI) is the first astronomical payload on the International Space Station (ISS). MAXI was activated on 3 August 2009 by receiving electric power, circulated coolant, and data links from Japanese Experiment Module (JEM) "Kibo" Exposed Facility of ISS. All MAXI instruments have successfully passed the post-activation health check. MAXI has two types of X-ray cameras, GSC (Gas Slit Camera covering 2-30 keV with twelve proportional counters) and SSC (Solid state Slit Camera covering 0.5-12 keV with 32 X-ray CCD chips), and three support sensors, VSC (Visual Star Camera), RLG (Ring Laser Gyro), and GPSR (GPS Receiver). MAXI transfers telemetry data to the ground via data relay satellites. Having accumulated the GSC data for one ISS orbit (92 minutes), we released, on 18 August 2009, the "first light" image in which we can easily recognize about 20 bright Galactic sources. A preliminary analysis suggests that GSC achieved about 20-30 mCrab sensitivity in one orbit, mostly consistent with the pre-flight estimation. In January 2010, we started the public release of the MAXI light curves and images at http://maxi.riken.jp/ . We are preparing the automatic Internet transmission of the MAXI source detection alerts (MAXI Nova/Burst Alerts). The nominal mission life is five years.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(3) 585-604 2008年6月 査読有りThe black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005 October, while it was in a low/hard state with a 0.7-300 keV luminosity of 4.6 x 10(37) ergs(-1). The XIS and HXD spectra, spanning 0.7-400 keV, were reproduced successfully, incorporating a cool accretion disk and a hot Comptonizing corona. The corona is characterized by an electron temperature of similar to 100 keV, and two optical depths of similar to 0.4 and similar to 1.5, which account for the softer and harder continua, respectively. The disk has an innermost temperature of similar to 0.2keV, and is thought to protrude half way into the corona. The disk not only provides seed photons to the Compton cloud, but also produces a soft spectral excess, a mild reflection hump, and a weakly broadened iron line. A comparison with the Suzaku data on GRO J1655-40 reveals several interesting spectral differences, which can mostly be attributed to inclination effects, assuming that the disk has a flat geometry while the corona is grossly spherical. An intensity-sorted spectroscopy indicates that the continuum becomes less Comptonized when the source flares up on time scales of 1-200 s, while the underlying disk remains unchanged.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S25-S33 2008年2月 査読有りThe hard X-ray detector (HXD) aboard the X-ray satellite Suzaku is designed to have a good timing capability with a 61 its time resolution. In addition to detailed descriptions of the HXD timing system, results of in-orbit timing calibration and the performance of the HXD are summarized. The relative accuracy of time measurements of the HXD event was confirmed to have an accuracy of 1.9 x 10(-9) s s(-1) per day, and the absolute timing was confirmed to be accurate to 360 mu s or better. The results were achieved mainly through observations of the Crab pulsar, including simultaneous ones with RXTE, INTEGRAL, and Swift.
-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S231-S239 2008年2月 査読有りWe report on the detection of a transient X-ray source toward the Small Magellanic Cloud (SMC) using the X-ray Imaging Spectrometer (XIS) on board the Suzaku telescope. The source was detected at the edge of the XIS image during a routine observation of the calibration source 1E0102.2-7219, a supernova remnant in the SMC. We constrained the source position using ray-tracing simulations. No such transient source was found at the position in the other Suzaku observations, nor in all of the available archived images of other X-ray missions for the last similar to 28 years. The XIS spectrum can be explained by a single blackbody with a temperature of similar to 72 eV, and an interstellar extinction of similar to 4.9 x 10(20) H atoms cm(-2), consistent with the value to the SMC. An additional absorption edge at similar to 0.74 keV was also confirmed, which is presumably due to absorption by helium-like oxygen ions. Assuming that the source is at the distance of the SMC, the X-ray luminosity in the 0.2-2.0 keV band is similar to 10(37) erg s(-1) and the radius of the source is similar to 10(8) cm. The XIS light curve shows about a two-fold decline in X-ray flux during the 24 ks observation. Together with the archived data, the X-ray flux in the burst is at least three-orders of magnitude brighter than the undetected quiescent level. All of these properties are often seen among supersoft sources (SSSs). We conclude that the transient source is another example of SSS in the SMC.
MISC
116-
ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVI 521 205-208 2019年We are developing the web-based quick data analysis tools JUDO2 and UDON2 at DARTS (http: //darts.isas.jaxa.jp). JUDO2 adopts Aladin Lite to display various astronomical survey data. In particular, we have created HiPS data of Suzaku, MAXI, ASCA and Swift, and publish them from DARTS. In addition, we made various types of the constellation data in HiPS format. Recently, thanks to cooperation by ESA-sky team, the XMM fields of view (footprints) and direct links to the XMM-archive at ESA are made available in JUDO2. UDON2 allows users to extract spectra and light-curves of MAXI, Suzaku and ASCA data. Users can display favorite targetstars or sky regions in JUDO2, and jump to UDON2 to quickly analyze these targets. We are going to add JAXA's other astronomical data (e.g. Akari pointing data, Hitomi) to JUDO2 and UDON2.
-
ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVIII 523 515-518 2019年CALET (CALorimetric Electron Telescope) has been installed and operational on the Japanese Experiment Module Exposed Facility of the International Space Station (ISS) since August 2015. We describe the Web analaysis system for the CALET Gamma-ray Burst Monitor (CGBM), which is publicly available from DARTS.
-
ASTRONOMICAL DATA ANALYSIS SOFTWARE AND SYSTEMS XXVI 521 46-49 2019年Over the past few years the Hierarchical Progressive Survey (HiPS) has become a key method for the distribution of all -sky reference data. Today, HiPS represents about 100 TB of data, and is expected to double each year as the network of a dozen of HiPS providers including ESAC, JAXA, CADC and CDS grows. HiPS data sets are used by thousands of users per day through various HiPS aware clients: Aladin, MIZAR, Aladin Lite, and Aladin-Lite based ESASky and JUDO2. We expect that this technology will be one of the main methods for the distribution of surveys - images, catalogs and cubes - for the next decade. In this extremely fast growing environment, we will discuss why the HiPS network is an excellent candidate for long term management of all-sky reference data. We highlight how the intrinsic HiPS architecture based on the well known HEALPix geometry, a simple tile structure, straightforward distribution method based only on a basic HTTP server, and being standardised by IVOA, constitutes an extremely robust foundation for a system which will support all-sky data distribution for a long time.
講演・口頭発表等
14-
JpGU-AGU Joint Meeting 2020:Virtual ユニオンセッション U-12 「地球惑星科学の進むべき道10 ビッグデータとオープンサイエンス」 2020年7月15日 招待有り
-
20 Years of Chandra Science Symposium
-
The 29th annual international Astronomical Data Analysis Software & Systems (ADASS)
所属学協会
1共同研究・競争的資金等の研究課題
5-
日本学術振興会 科学研究費助成事業 基盤研究(C) 2016年4月 - 2019年3月
-
日本学術振興会 科学研究費助成事業 基盤研究(C) 2009年 - 2011年
-
日本学術振興会 科学研究費助成事業 基盤研究(B) 2007年 - 2009年
-
日本学術振興会 科学研究費助成事業 国際学術研究 1992年 - 1994年
-
日本学術振興会 科学研究費助成事業 奨励研究(特別研究員) 1990年 - 1990年
