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 助教
- 学位
- 博士(理学)(2002年3月 東京大学理学系研究科物理学専攻)
- J-GLOBAL ID
- 202001017082346100
- researchmap会員ID
- R000012159
経歴
10-
2019年4月 - 現在
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2018年4月 - 2019年3月
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2017年4月 - 2018年3月
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2016年4月 - 2017年3月
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2011年4月 - 2016年3月
学歴
2-
1999年4月 - 2002年3月
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1997年4月 - 1999年3月
受賞
2論文
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りSuzaku observations are reported of the three giant radio galaxies, 3C 35, 3C 326, and DA 240, with a projected linear size of greater than or similar to 1 Mpc. The low and stable instrumental background of the X-ray Imaging Spectrometer onboard Suzaku allows a significant detection of inverse Compton X-ray emission from the lobes of these giant radio galaxies. As a result, the electron and magnetic energy densities in the lobes were measured. Based on the measurements, the late phase in the evolution of the energetics associated with jets from active galactic nuclei was investigated. It is found that the lobes of giant radio galaxies tend to reside in a near equipartition condition between electrons and magnetic field, despite the fact that smaller sources with sizes of about 100 kpc exhibit a particle dominance by a typical factor of 10 in energy density. In addition, the energy densities in the giant lobes are measured to be smaller by an order of magnitude as compared to the extrapolation of the size to energy density correlation found for smaller radio galaxies. These results indicate that typical radio galaxies experience a significant reduction in their jet power, as their jets evolve in size from 100 kpc to 1 Mpc.
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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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S947-S955 2011年11月 査読有りA careful analysis of the Suzaku data of the giant radio galaxy DA 240, of which the size is 1.48 Mpc, revealed diffuse X-ray emission associated with its east lobe. The diffuse X-ray spectrum was described with a simple power-law model with a photon index of Gamma = 1.92(-0.17-0.06)(+0.13+0.04) where the first and second errors represent the statistical and systematic ones. The agreement with the synchrotron radio photon index, Gamma(R) = 1.95 +/- 0.01 in 326-608.5 MHz, ensures that any excess X-ray emission is attributed to inverse Compton emission from the synchrotron-radiating electrons, boosting up the cosmic microwave background photons. From the X-ray flux density, 51.5 +/- 3.91(-5.4)(+6.2) nJy at 1 keV, derived with the photon index fixed at Gamma(R), in comparison with the synchrotron radio intensity of 10.30 +/- 0.12 Jy at 326 MHz, the magnetic and electron energy densities were estimated as u(m) = (3.0 +/- 0.2 +/- 0.4) x 10(-14)erg cm(-3) and u(e) =(34(-0.2-0.4)(+0.3+0.5)) x 10(-14)erg cm(-3) integrated over the electron Lorentz factor of 10(3)-10(5), respectively. Thus, the east lobe is found to reside in an equipartition condition between the electrons and magnetic field parametrized as u(e)/u(m) = 1.1(-0.1-0.2)(+0.2+0.4). The east lobe of DA 240 is indicated to exhibit the lowest value of tie, among all of the X-ray detected lobes of radio galaxies. A comparison of the energetics in the giant radio galaxies with a size of 1 Mpc to those in the smaller objects suggests a possibility that radio galaxies lose their jet power as they evolve from similar to 100 kpc to similar to 1 Mpc.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S1035-S1040 2011年11月The monitor of the all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB 090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst had a peculiarly narrow spectral energy distribution, which can be represented by a Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from a low baryon-load GRB fireball. Calculating the parameter of the fireball, we found the size of the base of the flow to be r(0) = (4.3 +/- 0.9) x 10(9) Y'(-3/2) cm, the Lorentz factor of the plasma is Gamma = (110 +/- 10) Y'(1/4), where Y' is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This r(0) is a factor of a few times larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S803-S811 2011年11月We present the results of monitoring the galactic black hole candidate GX 339-4 with the Monitor of All-sky X-ray Image (MAXI)/Gas Slit Camera in the high/soft state during an outburst in 2010. All of the spectra throughout the 8-month period were well reproduced with a model consisting of multi-color disk emission and its Comptonization component, whose fraction is <= 25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at R-in = 61 +/- 2 km for an inclination angle of i = 46 degrees and a distance of d = 8 kpc. This R-in, value is consistent with those of past measurements with Tenma in the high/soft state. Assuming that the disk extends to the innermost stable circular orbit of a non-spinning black hole, we estimate the black hole mass to be M = 6.8 +/- 0.2 M-circle dot for i = 46 degrees and d = 8 kpc, which is consistent with that estimated from the Suzaku observation of the previous low/hard state. Further combined with the mass function, we obtained a mass constraint of 4.3 M-circle dot < M < 13.3 M-circle dot for the allowed range of d = 6-15 kpc and i < 60 degrees. We also discuss the spin parameter of the black hole in GX 339-4 by applying relativistic accretion disk models to the Swift/XRT data.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S677-S689 2011年11月We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes (vertical bar b vertical bar > 10 degrees), produced from the first 7-month data (2009 September 1 to 2010 March 31) of the Gas Slit Camera in the 4-10 keV band. We have developed an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above the 7 sigma significance level with a limiting sensitivity of similar to 1.5 x 10(-11) erg cm(-2)s(-1) (1.2 mCrab) in the 4-10 keV band. Among them, we have identified 38 Galactic/LMC/SMC objects, 48 galaxy clusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Four other sources are confused with multiple objects, and one remains unidentified. The log N-log S relation of extragalactic objects is in good agreement with the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantly changed since that produced 30 yr ago.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S623-S634 2011年11月The Gas Slit Camera (GSC) is an X-ray instrument on the MAXI (Monitor of All-sky X-ray Image) mission aboard the International Space Station. It is designed to scan the entire sky every 92-minute orbital period in the 2-30 keV band and to achieve the highest sensitivity among the X-ray all-sky monitors ever flown so far. The GSC employs large-area position-sensitive proportional counters with a total detector area of 5350 cm(2). The on-board data processor has functions to format telemetry data as well as to control the high voltage of the proportional counters so as to protect them from particle irradiation. This paper describes the instruments, on-board data processing, telemetry data formats, and performance specifications expected from ground calibration tests.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S821-S825 2011年11月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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S635-S644 2011年11月We report on the in-orbit performance of the Gas Slit Camera (GSC) on the MAXI (Monitor of All-sky X-ray Image) mission carried on the International Space Station (ISS). Its commissioning operation, which started on 2009 August 8, confirmed the basic performances of the effective area in the energy band of 2-30 keV, the spatial resolution of the slit-and-slat collimator and detector with 1.5 FWHM, the source visibility of 40-150 seconds for each scan cycle, and the sky coverage of 85% per 92-minute orbital period and 95% per day. The gas gains and read-out amplifier gains have been stable within 1%. The background rate is consistent with the past X-ray experiments operated at a similar low-earth orbit if its relation with the geomagnetic cutoff rigidity is extrapolated to high latitude. We also present the status of the in-orbit operation and a calibration of the effective area and the energy response matrix using Crab-nebula data.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S937-S945 2011年11月We constructed a new X-ray (2-10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4-10 keV band. The sample consists of 37 non-blazar AGNs at z = 0.002-0.2, whose identification is highly (>97%) complete. We confirmed the trend that the fraction of absorbed AGNs with N-H > 10(22) cm(-2) rapidly decreases against the luminosity (L-X), from 0.73 +/- 0.10 at L-X = 10(42-43.5) erg s(-1) to 0.12 +/- 0.08 at L-X = 10(43.5-45.5) erg s(-1). The obtained luminosity function was well-fitted with a smoothly connected double power-law model whose indices are gamma(1) = 0.84 (fixed) and gamma(2) = 2.0 +/- 0.2 below and above the break luminosity, L-* = 10(43.3 +/- 10-4) erg s(-1), respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at L-X greater than or similar to 10(43.5) erg s(-1), it gives a larger number density at the lower luminosity range. A comparison between our luminosity function in the 2-10 keV band and that in the 14-195 keV band obtained from the Swift/BAT survey indicates that the averaged broad-band spectra in the 2-200 keV band should depend on the luminosity, approximated by Gamma similar to 1.7 for L-X less than or similar to 10(44) erg s(-1), while Gamma - 2.0 for L-X greater than or similar to 1044 erg s(-1). This trend was confirmed by the correlation between the luminosities in the 2-10 keV and 14-195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S505-S521 2011年3月 査読有りWe present new imaging at 12.81 and 11.7 mu m of the central similar to 40 '' x 30 '' (similar to 0.7 kpc x 0.5 kpc) of the starburst galaxy M 82. The observations were carried out with the COMICS mid-infrared (mid-IR) imager on the 8.2 m Subaru Telescope, and are diffraction-limited at an angular resolution of <0.'' 4. The images show extensive diffuse structures, including a 7 ''-long linear chimneylike feature and another resembling the edges of a ruptured bubble. This is the clearest view to date of the base cif the kpc-scale dusty wind known in this galaxy. These structures do not trace back to a single central point, implying multiple ejection sites for the dust. In general, the distribution of dust probed in the mid-IR anticorrelates with the locations of massive star clusters that appear in the near-infrared. The 10-21 mu m mid-IR emission, spatially integrated over the field of view, may be represented by hot dust with temperature of similar to 160 K. Most discrete sources are found to have extended morphologies. Several radio H II regions are identified for the first time in the mid-IR. The only potential radio supernova remnant to have a mid-IR counterpart is a source which has previously also been suggested to be a weak active galactic nucleus. This source has an X-ray counterpart in Chandra data which appears prominently above 3 keV and is best described as a hot (similar to 2.6 keV) absorbed thermal plasma with a 6.7 keV Fe K emission line, in addition to a weaker and cooler thermal component. The mid-IR detection is consistent with the presence of strong [Ne II]lambda 12.81 mu m line emission. The broad-band source properties are complex, but the X-ray spectra do not support the active galactic nucleus hypothesis. We discuss possible interpretations regarding the nature of this source.
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ASTROPHYSICAL JOURNAL 727(2) 2011年2月 査読有りThe Suzaku observation of a giant radio galaxy 3C 35 revealed faint extended X-ray emission, associated with its radio lobes and/or host galaxy. After careful subtraction of the X-ray and non-X-ray background and contaminating X-ray sources, the X-ray spectrum of the faint emission was reproduced by a sum of the power-law (PL) and soft thermal components. The soft component was attributed to the thermal plasma emission from the host galaxy. The photon index of the PL component, Gamma = 1.35(-0.86-0.10)(+0.56+0.11),where the first and second errors represent the statistical and systematic ones, was found to agree with the synchrotron radio index from the lobes, Gamma(R) = 1.7. Thus, the PL component was attributed to the inverse Compton (IC) X-rays from the synchrotron electrons in the lobes. The X-ray flux density at 1 keV was derived as 13.6 +/- 5.4(-3.6)(+4.0) nJy with the photon index fixed at the radio value. The X-ray surface brightness from these lobes (similar to 0.2 nJy arcmin(-2)) is lowest among the lobes studied through the IC X-ray emission. In combination with the synchrotron radio flux density, 7.5 +/- 0.2 Jy at 327.4 MHz, the electron energy density spatially averaged over the lobes was evaluated to be the lowest among those radio galaxies, as u(e) = (5.8 +/- 2.3(-1.7)(+1.9)) x 10(-14) erg cm(-3) over the electron Lorentz factor of 10(3) - 10(5). The magnetic energy density was calculated as u(m) = (3.1(-1.0-0.9)(+2.5+1.4)) x 10(-14) erg cm(-3), corresponding to the magnetic field strength of 0.88(-0.16-0.14)(+0.31+0.19) mu G. These results suggest that the energetics in the 3C 35 lobes are nearly consistent with equipartition between the electrons and magnetic fields.
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日本物理学会講演概要集 66 106-106 2011年 査読有り
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JETS AT ALL SCALES (275) 184-185 2011年 査読有りWe performed mapping observations of the Fornax A west lobe with Suzaku in order to measure X-ray brightness distribution. Thanks to the low and stable background of Suzaku, we succeeded in detecting the faint diffuse X-ray emission from the west lobe. Performing careful corrections to the obtained images, we finally measured the X-ray brightness profile extending over the lobe. By comparing the X-ray and radio profiles, the magnetic field found to be fairly constant at similar to 1 mu G over the lobe, while the electron energy distribution is suggested to concentrate on the lobe center.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(6) L55-L60 2010年12月Strong X-ray flares from the blazar Mrk 421 were detected in 2010 January and February through 7-month monitoring with the MAXI GSC. The maximum 2-10 keV flux in the January and February flares was measured to be 120 +/- 10 mCrab and 164 +/- 17 mCrab, respectively; the latter is the highest among those reported from the object. A comparison of the MAXI and Swift BAT data suggests a convex X-ray spectrum with an approximated photon index of Gamma greater than or similar to 2. This spectrum is consistent with a picture that MAXI is observing near the synchrotron peak frequency. The source exhibited a spectral variation during these flares, slightly different from those in previous observations, in which the positive correlation between the flux and hardness was widely reported. By equating the halving decay timescale in the January flare, t(d) similar to 2.5 x 10(4)s, to the synchrotron cooling time, the magnetic field was evaluated to be B similar to 4.5 x 10(-2)G (delta/10)(-1/3), where delta is the jet beaming factor. Assuming that the light crossing time of the emission region is shorter than the doubling rise time, t(r) less than or similar to 2 x 10(4)s, the region size was roughly estimated as R < 6 x 10(15)cm (delta/10). These results are consistent with values previously reported. For the February flare, the rise time, t(r) < 1.3 x 10(5)s, gives a loose upper limit on the size as R < 4 x 10(16)cm (delta/10), although the longer decay time, t(d) similar to 1.4 x 10(5)s, indicates B similar to 1.5 x 10(-2)G (delta/10)(-1/3), which is weaker than the previous results. This could be reconciled by invoking a scenario that this flare is a superposition of unresolved events with a shorter timescale.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(5) L27-L32 2010年10月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.
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The Astrophysical Journal 714(1) 37-44 2010年5月1日 査読有りUsing deep Chandra Advanced CCD Imaging Spectrometer (ACIS) observation data for Cygnus A, we report evidence of non-thermal X-ray emission from radio lobes surrounded by a rich intracluster medium (ICM). The diffuse X-ray emission, which is associated with the eastern and western radio lobes, was observed in a 0.7-7 keV Chandra ACIS image. The lobe spectra are reproduced with not only a single-temperature Mekal model, such as that of the surrounding ICM component, but also an additional power-law (PL) model. The X-ray flux densities of PL components for the eastern and western lobes at 1 keV are derived as 77.7+28.9 -31.9 nJy and 52.4+42.9 -42.4 nJy, respectively, and the photon indices are 1.69 +0.07 -0.13 and 1.84+2.90 -0.12, respectively. The non-thermal component is considered to be produced via the inverse Compton (IC) process, as is often seen in the X-ray emission from radio lobes. From a re-analysis of radio observation data, the multiwavelength spectra strongly suggest that the seed photon source of the IC X-rays includes both cosmic microwave background radiation and synchrotron radiation from the lobes. The derived parameters indicate significant dominance of the electron energy density over the magnetic field energy density in the Cygnus A lobes under the rich ICM environment. © 2010. The American Astronomical Society. All rights reserved..
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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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(5) 941-948 2009年10月 査読有りThe Suzaku X-ray satellite observed the nearby spiral galaxy NGC 4258 for a total good exposure time of 100 ks. We present an analysis of the Suzaku XIS data, in which we confirm that the 0.5-2 keV spectra of the interstellar medium (ISM) are well-represented by a two-temperature model. The cool and hot ISM temperatures are 0.23 +/- 0.01 and 0.58 +/- 0.01 keV, respectively. Suzaku's excellent spectral sensitivity has enabled us to measure the metal abundances of O, Ne, Mg, Si, and Fe of the ISM for the first time. The resultant abundance pattern of 0, Mg, Si, and Fe is consistent with that of the new solar abundance table of Lodders (2003, ApJ, 591, 1220), rather than Anders and Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197). This suggests that the metal enrichment processes of NGC 4258 and of our Galaxy are similar.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(5) 1011-1022 2009年10月 査読有りSuzaku observations of the blazar OJ 287 were performed in 2007 April 10-13 and November 7-9. They correspond to a quiescent and a flaring state, respectively. The X-ray spectra of the source can be well-described with single power-law models in both exposures. The derived X-ray photon index and the flux density at 1 keV were found to be Gamma = 1.65 +/- 0.02 and S-1 (keV) = 215 +/- 5 nJy in the quiescent state. In the flaring state, the source exhibited a harder X-ray spectrum (Gamma = 1.50 +/- 0.01) with a nearly doubled X-ray flux density of S-1 keV = 404(-5)(+6) nJy Moreover, significant hard X-ray signals were detected up to similar to 27 keV. In cooperation with Suzaku, simultaneous radio, optical, and very-high-energy gamma-ray observations of OJ 287 were performed with the Nobeyama Millimeter Array, the KANATA telescope, and the MAGIC telescope, respectively. The radio and optical fluxes in the flaring state (3.04 +/- 0.46 Jy and 8.93 +/- 0.05 mJy at 86.75 Hz and in the V-band, respectively) were found to be higher by a factor of 2-3 than those in the quiescent state (1.73 +/- 0.26 Jy and 3.03 +/- 0.01 mJy at 86.75 Hz and in the V-band, respectively). No notable gamma-ray events were detected in either observation. The spectral energy distribution of OJ 287 indicated that the X-ray spectrum was dominated by inverse Compton radiation in both observations, while synchrotron radiation exhibited a spectral cutoff at around the optical frequency. Furthermore, no significant difference in the synchrotron cutoff frequency was found between the quiescent and flaring states. According to a simple synchrotron self-Compton model, the change of the spectral energy distribution is due to an increase in the energy density of electrons with small changes of both the magnetic field strength and the maximum Lorentz factor of electrons.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(5) 999-1010 2009年10月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.
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31st International Cosmic Ray Conference, ICRC 2009 2009年We performed simultaneous multiwavelength observations of OJ 287 with the Nobeyama Millimeter Array for radio, the KANATA telescope and the KVA telescope for optical, the Suzaku satellite for X-ray and the MAGIC telescope for very high energy (VHE) γ-ray in 2007. The observations were conducted for a quiescent state in April and in a flaring state in November-December. We clearly observed increase of fluxes from radio to X-ray bands during the flaring state while MAGIC could not detect significant VHE γ-ray emission from the source. We could derive an upper limit (95% confidence level) of 1.7% of the Crab Nebula flux above 150 GeV from about 41.2 hours of the MAGIC observation. A simple SSC model suggests that the observed flaring activity could be caused by evolutions in the distribution of the electron population rather than changes of the magnetic field strength or Doppler beaming factor in the jet.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S279-S289 2009年1月 査読有りA Suzaku observation of an ultraluminous X-ray source, NGC 2403 Source 3, performed on 2006 March 16-17, is reported. The Suzaku XIS spectrum of Source 3 was described as multi-color black-body-like emission from an optically thick accretion disk. The innermost disk temperature and radius were measured to be T-in = 1.08(-0.03)(+0.02) keV and R-in = 122.1(-6.8)(+7.7)alpha(1/2) km, respectively, where alpha = (cos 60 degrees/cos i) with i being the disk inclination. Its bolometric luminosity was estimated to be L-bol = 1.82 x 10(39)alpha erg s(-1). Archival Chandra and XMM-Newton data of the source were analyzed. In almost all observations, the source showed multi-color black-body-like X-ray spectra with parameters similar to those of the Suzaku observation. In only one Chandra observation, however, Source 3 exhibited a power-law-like spectrum., with a photon index of Gamma = 2.37 +/- 0.08, when it was fainter by similar to 15% than in the Suzaku observation. This behavior is explained in terms of a transition between a slim-disk state and "very high" states, both found in Galactic black hole binaries, when their luminosity apporached the Eddington limit. These results are utilized to argue that ultraluminous X-ray sources generally have significantly higher masses than ordinary stellar-mass black holes.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S17-S33 2009年1月 査読有りSuzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10-600 keV, by utilizing PIN photodiodes and GSO scintillators; mounted in BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have an imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-Earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information, The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1 sigma systematic error is estimated to be less than 3% (PIN 15-40 keV) and 1% (GSO 50-100 keV) for more than 10 ks exposure.
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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.
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ASTROPHYSICAL JOURNAL 685(2) 828-838 2008年10月We investigate the total kinetic power (L-j) and age (t(age)) of powerful jets in FR II radio galaxies by comparison of the dynamical model of expanding cocoons with observations. We select four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219), for which the mass-density profiles of the intracluster medium (ICM) are known in the literature. It is found that large fractions greater than or similar to 0.02-0.7 of the Eddington luminosity (L-Edd) are carried away as kinetic power of jets. The upper limit of estimated 2L(j)/L-Edd is larger than unity (less than or similar to 10) for some sources, suggesting the possibility of super-Eddington mass accretions. As a consequence of the large powers, we also find that the total energy stored in the cocoon (E-c) exceeds the energy derived from the minimum energy condition for the energy of radiating nonthermal electrons and magnetic fields (E-min): 4 < E-c/E-min < 310. This implies that most of the energy in the cocoon is carried by invisible components such as thermal leptons (electron and positron) and/or protons.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S251-S261 2008年2月 査読有りSuzaku observed a nearby Seyfert 2 galaxy, NGC 4945, which hosts one of the brightest active galactic nuclei above 20keV. Combining data from the two detectors aboard Suzaku, the AGN intrinsic nuclear emission and its reprocessed signals were observed simultaneously. The intrinsic emission is highly obscured with an absorbing column of similar to 5 X 10(24) CM-2. The spectrum below 10 keV is dominated by a reflection continuum and emission lines from neutral/ionized material. Along with a neutral iron K alpha line, a neutral iron K alpha line and a neutral nickel Ka line were detected for the first time from this source. The neutral lines and the cold reflection continuum are consistent with both originating in the same location. The Compton down-scattered shoulder in the neutral Fe-K alpha line is similar to 10% in flux of the narrow core, which confirms that the line originates from reflection, rather than transmission. The flux of the intrinsic emission varied by a factor of similar to 2 within similar to 20 ks, which requires the obscuring material to be geometrically thin. Broadband spectral modeling showed that the solid angle of the neutral reflector is less than a few x 10(-2) x 2 pi. All of this evidence regarding the reprocessed signals suggests that a disk-like absorber/reflector is viewed from a near edge-on angle.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S293-S305 2008年2月 査読有りWe obtained a wide-band spectrum of the Compton-thick Seyfert 2 galaxy Mkn 3 with Suzaku. The observed spectrum was clearly resolved into weak, soft power-law emission, a heavily absorbed power-law component, cold reflection, and many emission lines. The heavily absorbed component, absorbed by gas with a column density of 1. 1 x 10(24) cm(-2), has an intrinsic 2-10 keV luminosity of similar to 1. 6 x 10(43) erg s(-1), and is considered to be direct emission from the Mkn 3 nucleus. The reflection component was interpreted as being the reflection of direct light off a cold, thick material; the reflection fraction, R, was 1.36 +/- 0.20. The cold material is inferred to be located > 1 pc from the central black hole of Mkn 3, due to the low ionization parameter of iron ( xi I erg cm s(-1)) and the narrow iron line width (sigma < 22 eV). The weak, soft power-law emission is considered to be scattered light by ionized gas with a scattering fraction of 0.9 +/- 0.2%. The existence of many highly ionized lines in the observed spectrum indicates that the ionized gas has a broad ionized structure, with xi = 10-1000 erg cm s(-1). This high-quality spectrum obtained by Suzaku can be considered to be a template for studies of Seyfert 2 galaxies.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(1) S241-S250 2008年2月An X-ray source, Suzaku J1305-4931, was discovered in the south-west arm of a nearby Seyfert II galaxy, NGC 4945, at 0.5-10 keV flux of 2.2 x 10(-12) erg cm(-2) s(-1) during a Suzaku observation conducted on 2006 January 15-17. It was undetectable in a shorter observation on 2005 August 22-23, with an upper limit of 1.7 x 10(-14) erg cm(-2) s(-1). At a distance of 3.7Mpc, the bolometric luminosity of the source became L-bol = 4.4 x 10(39)alpha erg s(-1), where a = (cos 60 degrees/cos i) and i is the disk inclination. The time-averaged X-ray spectrum of the source is described by a multi-color disk model, with an innermost disk temperature of T-in = 1.69(-0.05)(+0.06) keV. It varied by a factor of 2 in intensity, following a clear correlation of L-bol proportional to T-in(4). The innermost disk radius is inferred to stay constant at R-in = 79(-3.9)(+4.0)alpha(1/2) km, suggesting the presence of a standard accretion disk. Relating Rin with the last stable orbit around a non-rotating black hole yields a rather low black-hole mass, similar to 9 alpha(1/2) solar masses, which would imply that the source is shining at a considerable super-Eddington luminosity. These results can be better interpreted by invoking sub-Eddington emission from a rapidly spinning black hole with 20-130 solar masses.
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Proceedings of SPIE - The International Society for Optical Engineering 7011 2008年MAXI (Monitor of All-sky X-ray Image) is a payload on board the International Space Station, and will be launched on April 2009. We report on the current development status on MAXI, in particular on the two types of X-ray camera (GSC and SSC), and the simulation results of the MAXI observation. SSC is a CCD camera. The moderate energy resolution enables us to detect the various emission peak including 0.5 keV oxygen line. The averaged energy resolution at the CCD temperature of -70 deg is 144.5 eV (FWHM) for 5.9 keV X-ray. GSC includes proportional gas counters, which have large X-ray detection area (5350cm2). The averaged position resolution of 1.1mm at 8 keV enable us to determined the celestial position of bright sources within the accuracy of 0.1 degree. The simulation study involving the results of performance test exhibits the high sensitivity of MAXI as designed.
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Proceedings of SPIE - The International Society for Optical Engineering 7011 2008年Monitor of All-sky X-ray Image (MAXI) is an X-ray all-sky monitor, which will be delivered to the International Space Station (ISS) by a space shuttle crew in early 2009, to scan almost the entire sky once every 96 minutes for a mission life of two to five years. The detection sensitivity will be 5 mCrab (5σ level) for a one-day MAXI operation, 2 mCrab for one week, and 1 mCrab for one month, reaching a source confusion limit of 0.2 mCrab in two years. In this paper, brief descriptions are presented for the MAXI mission and payload, and three operation phases, 1) the launch-to-docking phase, 2) the initial in-orbit calibration phase, and 3) the routine operation phase. We also describes the MAXI data product and its release plan for public users.
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AIP Conference Proceedings 1000 592-595 2008年Monitor of All-sky X-ray Image (MAXI) will be launched and attached on the International Space Station (ISS) next year. MAXI scans the sky while ISS goes around the Earth and provides an all sky X-ray image every orbit. MAXI has two types of X-ray instruments: gas-proportional counters for 2-30 keV and CCD cameras for 0.5-10 keV. MAXI will be able to transmit alerts to the Internet on X-ray transients including bright X-ray afterglows. © 2008 American Institute of Physics.
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Astrophysics and Space Science 311(1-3) 335-339 2007年10月 査読有りWe investigate the total kinetic powers (L j) and ages (t age) of powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219) by the detail comparison of the dynamical model of expanding cocoons with observed ones. It is found that these sources have quite large kinetic powers with the ratio of L j to the Eddington luminosity (L Edd) resides in 0.02< L j/L Edd< 10. Reflecting the large kinetic powers, we also find that the total energy stored in the cocoon (E c) exceed the energy derived from the minimum energy condition (E min∈): 2< E c/E min∈< 160. This implies that a large amount of kinetic power is carried by invisible components such as thermal leptons (electron and positron) and/or protons. © 2007 Springer Science+Business Media B.V.
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ASTROPHYSICAL JOURNAL 665(1) 209-224 2007年8月 査読有りA Suzaku observation of the nucleus of the radio-loud AGN Centaurus A in 2005 has yielded a broadband spectrum spanning 0.3-250 keV. The net exposure times after screening were 70 ks per X-ray Imaging Spectrometer (XIS) camera, 60.8 ks for the Hard X- ray Detector (HXD) PIN, and 17.1 ks for the HXD GSO. The hard X- rays are fit by two power laws of the same slope, absorbed by columns of 1.5 and 7 x 10(23) cm(-2), respectively. The spectrum is consistent with previous suggestions that the power-law components are X- ray emission from the subparsec VLBI jet and from Bondi accretion at the core, but it is also consistent with a partial-covering interpretation. The soft band is dominated by thermal emission from the diffuse plasma and is fit well by a two-temperature VAPEC model, plus a third power-law component to account for scattered nuclear emission, jet emission, and emission from X- ray binaries and other point sources. Narrow fluorescent emission lines from Fe, Si, S, Ar, Ca, and Ni are detected. The Fe K proportional to line width yields a 200 lt-day lower limit on the distance from the black hole to the line-emitting gas. Fe, Ca, and S K-shell absorption edges are detected. Elemental abundances are constrained via absorption edge depths and strengths of the fluorescent and diffuse plasma emission lines. The high metallicity ([Fe/H] = +0.1) of the circumnuclear material suggests that it could not have originated in the relatively metal-poor outer halo unless enrichment by local star formation has occurred. Relative abundances are consistent with enrichment from Type II and Ia supernovae.
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (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.) 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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Proceedings of SPIE - The International Society for Optical Engineering 6686 2007年MAXI is the first payload to be attached on JEM-EF (Kibo exposed facility) of ISS. It provides an all sky X-ray image every ISS orbit. If MAXI scans the sky during one week, it could make a milli-Crab X-ray all sky map excluding bright region around the sun. Thus, MAXI does not only inform X-ray novae and transients rapidly to world astronomers if once they occur, but also observes long-term variability of Galactic and extra-Galactic X-ray sources. MAXI also provides an X-ray source catalogue at that time with diffuse cosmic X-ray background. MAXI consists of two kinds of detectors, position sensitive gas-proportional counters for 2-30 keV X-rays and CCD cameras for 0.5-10 keV X-rays. All instruments of MAXI are now in final phase of pre-launching tests of their flight modules. We are also carrying out performance tests for X-ray detectors and collimators. Data processing and analysis software including alert system on ground are being developed by mission team. In this paper we report an overview of final instruments of MAXI and capability of MAXI.
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AIP Conference Proceedings 921 440-441 2007年MAXI is an all sky X-ray monitor to be mounted on the Japanese Experimental Module in the International Space Station (ISS). It scans almost all over the sky every 96 minutes, in the course of the orbital motion of the ISS. MAXI is designed to have a sensitivity, significantly higher than the previous X-ray monitors, and then, to detect X-ray sources as faint as 1 mCrab in a week observation. Therefore, MAXI is expected to create a novel catalogue of not only the stable X-ray sources but also the highly variable ones in the sky, especially active galactic nuclei for the first time. If MAXI detects X-ray phenomena, alerts will be quickly made through the Internet. © 2007 American Institute of Physics.
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Publications of the Astronomical Society of Japan 59(2) 279-297 2007年We report on deep (40 ks × 4) observations of the bright broad line radio galaxy 3C 120 using Suzaku. The observations were spaced one week apart, and sampled a range of continuum fluxes. An excellent broadband spectrum was obtained over two decades of frequency (0.6 to 50keV) within each 40 ks exposure. We clearly resolved the iron K emission-line complex, finding that it consists of a narrow Kα core (σ ≃ 110eV or an EW of 60 eV), a 6.9 keV line, and an underlying broad iron line. Our confirmation of the broad line contrasts with the XMM-Newton observation in 2003, where the broad line was not required. The most natural interpretation of the broad line is iron K line emission from a face-on accretion disk that is truncated at ∼ 10 r g. Above 10 keV, a relatively weak Compton hump was detected (reflection fraction of R ≃ 0.6), superposed on the primary X-ray continuum of Γ ≃ 1.75. Thanks to the good photon statistics and low background of the Suzaku data, we clearly confirm the spectral evolution of 3C 120, whereby the variability amplitude decreases with increasing energy. More strikingly, we discovered that the variability is caused by a steep power-law component of Γ ≃ 2.7, possibly related to non-thermal jet emission. We discuss our findings in the context of similarities and differences between radio-loud/quiet objects. © 2007. Astronomical Society of Japan.
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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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Journal of Physics: Conference Series 31(1) 201-202 2006年3月22日By using analytical model of cocoon expansion, we examine the total power and age of jets in five FRII radio galaxies. The estimated total power is quite larger than those estimated in previous works based on observation of non-thermal emission from electrons. This might imply that the amount of unobservable particles (e.g. protons and thermal component) can not be ignored when considering jet dynamics. © 2006 IOP Publishing Ltd.
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PROCEEDINGS OF THE X-RAY UNIVERSE 2005, VOLS 1 AND 2 604 585-+ 2006年 査読有りIn an XMM-Newton observation of the east lobe of nearby radio galaxy Fonrax A, we have significantly detected the diffuse X-ray emission, which was originally discovered by ASCA and ROSAT. The X-ray spectrum of the diffuse emission is described by a single powerlaw model, modified with the Galactic absorption toward the object. The best-fit X-ray photon index, 1.62(-0.15)(+0.25), agrees well with the synchrotron radio index, 1.68 +/- 0.05, between 29.9 MHz and 5 GHz. Therefore, the inverse Compton interpretation for the diffuse X-ray emission is justified. A comparison between the radio and Xray flux densities gives a moderate electron-energy dominance over in the east lobe of Fornax A, in spite of the dormancy of its nucleus. We also reexamined the ASCA result on the west lobe, to find that both lobes share the similar physical condition.
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X-RAY AND GAMMA-RAY INSTRUMENTATION FOR ASTRONOMY XIII 5165 375-386 2004年 査読有りMAXI is an X-ray all-sky monitor which will be mounted on the Japanese Experimental Module (JEM) of the International Space Station (ISS) in 2008. The Gas Slit Camera (GSC) consists of 12 one-dimensional position sensitive proportional counters and the sensitivity will be as high as 1 mCrab for a one-week accumulation in the 2-30 keV band. In order to calibrate the detectors and electronic systems thoroughly before the launch, a fast and versatile Ground Support Electronic (GSE) system is necessary. We have developed a new GSE based on VME I/O boards for a Linux workstation. These boards carry reconfigurable FPGAs of 100,000 gates, together with 16 Mbytes of SDRAM. As a demonstration application of using this GSE, we have tested the positional response of a GSC engineering counter. We present a schematic view of the GSE highlighting the functional design, together with a future vision of the ground testing of the GSC flight counters and digital associated processor.
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 490(3) 456-464 2002年9月 査読有りCerium-doped gadolinium silicic dioxide crystal, GSO(Ce), is a high-Z that gives higher light yield than BGO, and can potentially replace NaI(Tl), CsI(Tl) and BGO in many applications, Its production cost, however, has been substantially higher than any of them, while its energy resolution has been worse than that of NaI(Tl) or CsI(Tl). The merit did not overcome these deficiencies except in limited applications. We developed a low background phoswich counter (the well-type phoswich Counter) for the Hard X-ray Detector of the Astro-E project based on GSO scintillator. In the developmental work, we have succeeded in improving the light yield of GSO(Ce) by 40-50%. For energies above 500 keV, a large GSO(Ce) crystal (4.5 cm (.) 4.5phi cm) now gives energy resolution comparable to or better than the best NaI(Tl) when read out with a phototube. With a small GSO(Ce) crystal (5 x 5 x 5 mm(3)) and a photodiode, an energy resolution comparable to or better than the best CsI(Tl) has been obtained. With this improved performance, we find that the much higher photopeak efficiency and the shorter scintillation decay time of GSO(Ce) offsets its higher cost for many applications. We summarize our past developmental work to decrease radioactive contamination and to increase light yield of GSO(Ce) for astronomical hard X-ray detection. Included also are measurements done after the unsuccessful launch of the Astro-E mission. The work is still continuing for the remake version of Astro-E Hard X-ray Detector. (C) 2002 Elsevier Science B.V. All rights reserved.
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IEEE Transactions on Nuclear Science 49 I(4) 1893-1897 2002年8月This paper summarizes the design and performance of the hard X-ray detector constructed for the ASTRO-E satellite. The detector utilizes the GSO/BGO well-type phoswich counters in a compound-eye configuration to achieve an extremely low background level of a few × 10-5counts s-1 cm-2keV-1 [1]. The GSO scintillators installed in the BGO active shield wells are sensitive to 30-600 kev photons, while the 2-mm-thick silicon PIN diodes, placed in front of each GSO crystal, cover the 10-60 kev energy band with a spectral resolution of ∼3.5-keV full-width at half-maximum. The design goals, of both low background and high energy resolution, in the hard X-ray bands were verified through the preflight calibration experiments.
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PARTICLES AND FIELDS IN RADIO GALAXIES 250 394-399 2002年 査読有りASCA observation of the northern outer lobe edge region of the radio galaxy Centaurus A, similar to 3.5degrees north of its nucleus, is reported. Excess hard X-ray emission is seen around RA 13(hz)26m00(s), Dec. -39degrees20'00" (J2000 coordinates), together with soft diffuse X-ray emission extending all over the field of view of the GIS (similar to 50 arcmin in diameter). The spectrum of the soft diffuse emission is well described by an optically thin thermal plasma model with temperature kT similar to 0.6 keV modified by Galactic absorption. This emission is thought to arise from the thermal plasma associated with the outer lobe of Centaurus A and which has a thermal pressure of similar to 5 x 10(-13) dyn cm(-2). The excess hard emission is likely to be diffuse, and its spectrum is well described with a power law model of photon index similar to 1.7 or a thermal bremsstrahlung model of temperature kT greater than or similar to 11 keV. The nature of the hard emission is still unclear.
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2001 IEEE NUCLEAR SCIENCE SYMPOSIUM, CONFERENCE RECORDS, VOLS 1-4 1 483-486 2002年 査読有りThe ASTRO-E Hard X-ray Detector utilized GSO/BGO well-type phoswich counters in compound-eye configuration [1], to achieve an extremely low background level of a few x 10(-5)counts s(-1) cm(-2) keV(-1). The GSO scintillators installed in the BGO active shield wells observes 30-600 keV photons, while silicon PIN diodes of 2 mm thick placed in front of each GSO crystal covers 10 - 60 keV photons with energy resolution of similar to3.5 keV FWHM. The design goals both of low background and high energy resolution in the hard X-ray bands were confirmed to be achieved through the preflight calibration experiments.
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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 48(3) 379-384 2001年6月 査読有りThe energy-dependent response of the crystalline oxide scintillator Gd2SiO5:Ce3+ (GSO:Ce) is studied in the energy range from 14 to 662 keV as a part of the preflight calibration of the hard X-ray detector (HXD) onboard the ASTRO-E satellite. In the relation between photon energy deposited and light yields, there exists nonproportionality and discontinuity around the energy of the gadolinium K-edge (50.2 keV). In 16 GSO scintillator units of the HXD flight model, the same characteristics of the energy response are confirmed. To evaluate the response across the K-edge quantitatively, we measure the electron response" by means of the Compton coincidence technique. By using the electron response of the GSO crystal, we calculate the light yield nonproportionality as a function of deposited photon energy. We find that a photopeak line profile of the 59.5-keV emission of Am-241 is well modeled by a composite Gaussian. This will be discussed in terms of the light yield nonproportionality."
MISC
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VizieR On-line Data Catalog 2023年10月
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The 32nd Texas Symposium on Relativistic Astrophysics 2023年12月15日
共同研究・競争的資金等の研究課題
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日本学術振興会 科学研究費助成事業 2023年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2021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 2010年 - 2012年
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日本学術振興会 科学研究費助成事業 2008年 - 2011年
