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 主任研究開発員
- 研究者番号
- 90392810
- J-GLOBAL ID
- 202201019169253149
- researchmap会員ID
- R000042142
論文
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Publications of the Astronomical Society of Japan 2024年2月9日Abstract We develop a new deconvolution method to recover the precise Crab Nebula image taken by the Hitomi HXT, suppressing the artifact due to the bright Crab pulsar. We extend the Richardson–Lucy method, introducing two components corresponding to the nebula and pulsar with regularization for smoothness and flux, respectively, and performing simultaneous deconvolution of multi-pulse-phase images. The structures, including the torus and jets, seen in the deconvolved nebula image at the lowest energy band of 3.6–15 keV appear consistent with those identified in the high-resolution Chandra X-ray image. Above 15 keV, we confirm NuSTAR’s findings that the nebula size decreases in higher energy bands. We find that the north-east side of the nebula is fainter in higher energy bands. Our deconvolution method is applicable for any telescope images of faint diffuse objects containing a bright point source.
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Publications of the Astronomical Society of Japan 73(3) 716-727 2021年6月13日 査読有りSimultaneous X-ray and optical observations of black hole X-ray binaries have shown that the light curves contain multiple correlated and anti-correlated variation components when the objects are in the hard state. In the case of the black hole X-ray binary GX 339−4, the cross correlation function (CCF) of the light curves suggests a positive correlation with an optical lag of 0.15 s and anti-correlations with an optical lag of 1 s and X-ray lag of 4 s. This indicates that the two light curves have some common signal components with different delays. In this study we extracted and reconstructed those signal components from the data for GX 339−4. The results confirmed that correlation and anti-correlation with the optical lag are two common components. However, we found that the reconstructed light curve for the anti-correlated component indicates a positively correlated variation with an X-ray lag of ∼+1 s. In addition, the CCF for this signal component shows anti-correlations not only with the optical lag, but also with the X-ray lag, which is consistent with the CCF for the data. Therefore, our results suggest that the combination of the two positively correlated components, that is, the X-ray preceding signal with the 0.15 s optical lag and the optical preceding signal with the 1 s X-ray lag, can make the observed CCF without anti-correlated signals. The optical preceding signal may be caused by synchrotron emission in a magnetically dominated accretion flow or in a jet, while further study is required to understand the mechanism of the X-ray time lag.
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Publications of the Astronomical Society of Japan 2019年6月24日 査読有り<jats:title>Abstract</jats:title> <jats:p>We present an overview of a deep transient survey of the COSMOS field with the Subaru Hyper Suprime-Cam (HSC). The survey was performed for the 1.77 deg2 ultra-deep layer and 5.78 deg2 deep layer in the Subaru Strategic Program over six- and four-month periods from 2016 to 2017, respectively. The ultra-deep layer reaches a median depth per epoch of 26.4, 26.3, 26.0, 25.6, and 24.6 mag in g, r, i, z, and y bands, respectively; the deep layer is ∼0.6 mag shallower. In total, 1824 supernova candidates were identified. Based on light-curve fitting and derived light-curve shape parameter, we classified 433 objects as Type Ia supernovae (SNe); among these candidates, 129 objects have spectroscopic or COSMOS2015 photometric redshifts and 58 objects are located at z > 1. Our unique data set doubles the number of Type Ia SNe at z > 1 and enables various time-domain analyses of Type II SNe, high-redshift superluminous SNe, variable stars, and active galactic nuclei.</jats:p>
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 238(2) 2018年10月We present the third MAXI/GSC catalog in the high Galactic latitude sky (vertical bar b vertical bar > 10 degrees) based on the 7-year data from 2009 August 13 to 2016 July 31, complementary to that in the low Galactic latitude sky (vertical bar b vertical bar < 10 degrees) (Hori et al. 2018). We compile 682 sources detected at significances of s(D,4-10 keV) >= 6.5 in the 4-10 keV band. A two-dimensional image fit based on the Poisson likelihood algorithm (C-statistics) is adopted for the detections and constraints on their fluxes and positions. The 4-10 keV sensitivity reaches approximate to 0.48 mCrab, or approximate to 5.9 x 10(-12) erg cm(-2) s(-1), over half of the survey area. Compared with the 37-month Hiroi et al. (2013) catalog, which adopted a threshold of s(D,4-10) (keV) >= 7, the source number increases by a factor of similar to 1.4. The fluxes in the 3-4 keV and 10-20 keV bands are further estimated, and hardness ratios (HRs) are calculated using the 3-4 keV, 4-10 keV, 3-10 keV, and 10-20 keV band fluxes. We also make the 4-10 keV light curves in 1-year bins for all the sources and characterize their variabilities with an index based on a likelihood function and the excess variance. Possible counterparts are found from five major X-ray survey catalogs by Swift, Uhuru, RXTE, XMM-Newton, and ROSAT, as well as an X-ray galaxy cluster catalog (MCXC). Our catalog provides the fluxes, positions, detection significances, HRs, 1-year bin light curves, variability indices, and counterpart candidates.
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 235(1) 2018年3月We present the first MAXI/GSC X-ray source catalog in the low-Galactic-latitude sky vertical bar b vertical bar < 10 degrees outside the Galactic center region (vertical bar b vertical bar < 5 degrees, l < 30 degrees, and l > 330 degrees) based on 7-year data from 2009 August 13 to 2016 July 31. To overcome source confusion in crowded regions, we have accurately calibrated the position-dependent shape of the point-spread function of the MAXI/GSC by analyzing onboard data. We have also taken into account the Galactic ridge X-ray emission. Using a maximum likelihood image fitting method, we have detected 221 sources with a significance threshold >6.5 sigma, 7 of which are transients only detected in 73-day time-sliced images. The faintest source has a flux of 5.2 x 10(-12) erg cm(-2) s(-1) (or an intensity of 0.43 mCrab) in the 4-10 keV band. We have identified the counterparts for about 81% of the detected sources, by cross-matching with the Swift, Uhuru, RXTE, XMM-Newton, MCXC, and ROSAT all-sky survey catalogs. Our catalog contains the source name, position and its error, flux and detection significance in the 3-4. keV, 4-10. keV, and 10-20. keV bands, hardness ratios, and information on the likely counterpart for the individual detected sources. We have obtained 73-day bin light curves of all the cataloged sources over 7 years and have calculated their periodograms. On the basis of the mean properties of time variability and spectral hardness, we suggest that the majority of the unidentified sources are low-mass X-ray binaries or blazars. Finally, we present the log N-log S relations at different Galactic longitudes and for different source populations.
MISC
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Publications of the Astronomical Society of Japan 62(5) 1249-1259 2010年<jats:title>Abstract</jats:title> <jats:p>We report on the results of a Suzaku observation of the anomalous X-ray pulsar (AXP) 1E 1841$-$045 at the center of the supernova remnant Kes 73. We confirmed that the energy-dependent spectral models obtained by previous separate observations were also satisfied over a wide energy range from 0.4 to $\sim$70 keV, simultaneously. Here, the models below $\sim$10 keV were a combination of blackbody (BB) and power-law (PL) functions, or of two BBs with different temperatures at 0.6–7.0 keV (Morii et al. 2003, PASJ, 55, L45), and that above $\sim$20 keV was a PL function (Kuiper et al. 2004, ApJ, 613, 1173). The combination BB $+$ PL $+$ PL was found to best represent the phase-averaged spectrum. Phase-resolved spectroscopy indicated the existence of two emission regions, one with a thermal and the other with a non-thermal nature. The combination BB $+$ BB $+$ PL was also found to represent the phase-averaged spectrum well. However, we found that this model is physically unacceptable due to an excessively large area of the emission region of the blackbody. Nonetheless, we found that the temperatures and radii of the two blackbody components showed moderate correlations in the phase-resolved spectra. The fact that the same correlations have been observed between the phase-averaged spectra of various magnetars (Nakagawa et al. 2009, PASJ, 61, 109) suggests that a self-similar function can approximate the intrinsic energy spectra of magnetars below $\sim$10 keV.</jats:p>
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Publications of the Astronomical Society of Japan 61(5) 999-1010 2009年10月25日<jats:title>Abstract</jats:title> <jats:p>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 30 keV and X-ray CCDs covering the energy range of 0.5 to 12 keV. 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 $\sim $20 mCrab ($\sim $7 $\times$ 10$^{-10} $erg cm$^{-2} $s$^{-1}$ in the energy band of 2–30 keV) from observations during one ISS orbit (90 min), $\sim $4.5 mCrab for one day, and $\sim $2 mCrab for one week. The final detectability of MAXI could be $\sim $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.</jats:p>
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JAXA-SP-08-014E 114-119 2009年2月27日
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TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN 7(ists26) Tf_43-Tf_48 2009年MAXI (Monitor of All sky X-ray Image) is the first X-ray observation payload to be installed to EF (Exposed Facility) of Kibo (JEM: Japanese Experiment Module) on ISS (International Space Station). One of the important missions of MAXI is to quickly release novae or transient information of X-ray sources through its alert system to the worldwide astronomers. For this purpose, MAXI is equipped with a unique data transfer system both for the ground and on-board handling, which fully utilizes the communication system of ISS. The uniqueness of the data transfer system of MAXI comes from the fact that it is a payload of ISS, and is not seen in the ordinary payloads on free flyers (satellites). MAXI analyzes the observation data automatically in real time, and an alert for the novae or transient sources can be distributed widely through internet based on the analysis result. Various restrictions are imposed to keep tight security even on the ground system of ISS payloads. This paper describes the data transmission process in each stage, namely that in MAXI, the ISS communication links between the ISS and ground, and the process in the MAXI ground system.
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Publications of the Astronomical Society of Japan 60(2) 237-244 2008年4月25日<jats:title>Abstract</jats:title> <jats:p>A Suzaku TOO observation of CXOU J164710.2$-$455216 was performed on 2006 September 23–24 for a net exposure of 38.8 ks. Pulsations were clearly detected in the XIS light curves with a pulse period of 10.61063(2) s. The XIS pulse profile is found to be highly non-sinusoidal. It shows 3 peaks of different amplitudes with an RMS fractional amplitude of $\sim$11% in the 0.2–6.0 keV energy band. The 1–10 keV XIS spectra were well fitted by two different models consisting of a power-law and a blackbody component and two blackbody components, respectively. Although both the models are statistically acceptable, a difference in the pulse profiles at soft (0.2–6.0 keV) and hard (6–12 keV) X-rays favors the model consisting of two blackbody components. The temperatures of two blackbody components are found to be 0.61$\pm$0.01 keV and 1.22$\pm$0.06 keV, and the value of the absorption column density is 1.73$\pm$0.03 $\times$ 10$^{22}$atoms cm$^{-2}$. Pulse phase resolved spectroscopy shows that the flux of the soft blackbody component consists of three narrow peaks, whereas the flux of the other component shows a single peak over the pulse period of the AXP. The blackbody radii change between 2.2–2.7 km and 0.28–0.38 km (assuming the source distance to be 5 kpc) over the pulse phases for the soft and hard components, respectively. The details of the results obtained from the timing and spectral analyses are presented.</jats:p>
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Publications of the Astronomical Society of Japan 60(sp1) S231-S239 2008年2月20日<jats:p>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 $\sim$28 years. The XIS spectrum can be explained by a single blackbody with a temperature of $\sim$72 eV, and an interstellar extinction of $\sim$4.9$\times$10$^{20}$ H atoms cm$^{-2}$, consistent with the value to the SMC. An additional absorption edge at $\sim$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 $\sim$10$^{37}$ erg s$^{-1}$ and the radius of the source is $\sim$10$^{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.</jats:p>
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Publications of the Astronomical Society of Japan 59(sp1) S1-S7 2007年1月30日<jats:p>High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.</jats:p>
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SPIE Proceedings 6266 62663U 2006年6月14日
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The Astrophysical Journal 622(1) 544-548 2005年3月20日
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日本物理学会講演概要集 60.2.1 36 2005年
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Advances in Space Ressearch 35 1177-1180 2005年
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Astrophys. J 622 544-548 2005年
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Publications of the Astronomical Society of Japan 55(3) L45-48 2003年<jats:title>Abstract</jats:title> <jats:p>We present the results from a Chandra ACIS CC mode observation of an anomalous X-ray pulsar (AXP) 1E 1841$-$045. This was the first observation in which the pulsar spectrum over a wide energy range was spatially discriminated from the surrounding SNR, Kes 73. Like other AXPs, the phase-integrated spectrum was fitted well with a power-law plus blackbody model. The spectral parameters are $\Gamma = 2.0 \pm 0.3$, $kT_\mathrm{BB} = 0.44 \pm 0.02 \,\mathrm{keV}$, and $N_\mathrm{H} = 2.54^{+0.15}_{-0.13} \times 10^{22} \,\mathrm{cm}^{-2}$. This photon index is the flattest among AXPs, and resembles soft gamma-ray repeaters (SGRs) in a quiescent state. The pulse profile is double-peaked, and we found that the second peak has a significantly hard spectrum. The spectra of all phases are consistent with a power-law plus blackbody model with a constant temperature and photon index. When fitted with a two-blackbody model, we obtained a similarly good fit. These results can be interpreted by saying that there are two emission regions with different energy spectra.</jats:p>
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Neurologia medico-chirurgica 41(1) 1-7 2001年To elucidate whether a relationship exists between the site of trauma and severity of acute hyperextension spinal cord injury without bone damage, we examined the clinical features of 25 male and 10 female patients aged 13 to 88 years. None of the patients had vertebral damage such as fracture and dislocation. The site of impact was classified as the buccal, forehead, or mandibular region. The neurological findings were assessed according to Frankel's classification at admission and at follow up after 3 months or more to assess outcome. Eleven patients suffered trauma in the buccal region, one patient in Frankel's grade B, three in grade C, and seven in grade D at admission. All 11 of these patients showed an improvement of one grade or more to an outcome of C in one patient, D in one, and E in nine. Trauma occurred at the forehead region in 18 patients, four in grade B, 10 in grade C, and four in grade D. Improvement was seen at follow up by one grade or more to C in one patient, D in 10, and E in seven. Trauma occurred at the mandibular region in six patients, four in grade B and two in grade C. Four of these patients showed improvement of one grade or more to grade B in one, grade C in four, and grade E in one. Overall, seven patients had poor outcomes, five of whom suffered trauma to the mandibular region, indicating that impact to the mandibular region tends to have an unfavorable clinical outcome. Our findings indicate that the site of trauma greatly influences the severity of hyperextension spinal cord injury.<br>
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 2022年4月 - 2025年3月
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日本学術振興会 科学研究費助成事業 2017年4月 - 2020年3月
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日本学術振興会 科学研究費助成事業 2011年 - 2013年
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日本学術振興会 科学研究費助成事業 2009年 - 2010年
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日本学術振興会 科学研究費助成事業 2007年 - 2009年
