Takeshi Go Tsuru

Kyoto University, Kioto, Kyoto, Japan

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Publications (176)230.41 Total impact

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    ABSTRACT: The stellar distribution derived from an H- and KS-band survey of the central region of our Galaxy is compared with the Fe xxv Kα (6.7 keV) line intensity observed with the Suzaku satellite. The survey is for the galactic coordinates |l| ≲ 3$_{.}^{\circ}$0 and |b | ≲ 1$_{.}^{\circ}$0 (equivalent to 0.8 kpc × 0.3 kpc for R⊙ = 8 kpc), and the number-density distribution N(KS,0; l, b) of stars is derived by using the extinction-corrected magnitude KS,0 = 10.5. This is deep enough to probe the old red-giant population and in turn to estimate the (l, b) distribution of faint X-ray point sources such as coronally active binaries and cataclysmic variables. In the Galactic plane (b = 0°), N(10.5; l, b) increases in the direction of the Galactic center as |l|−0.30±0.03 in the range of − 0$_{.}^{\circ}$1 ≥ l ≥ − 0$_{.}^{\circ}$7, but this increase is significantly slower than the increase (|l|−0.44±0.02) of the Fe xxv Kα line intensity. If normalized with the ratios in the outer region 1$_{.}^{\circ}$5 ≤ |l| ≤ 2$_{.}^{\circ}$8, where faint X-ray point sources are argued to dominate the diffuse Galactic X-ray ridge emission, the excess of the Fe xxv Kα line intensity over the stellar number density is at least a factor of two at |l| = 0$_{.}^{\circ}$1. This indicates that a significant part of the Galactic-center diffuse emission arises from a truly diffuse optically thin thermal plasma, and not from an unresolved collection of faint X-ray point sources related to the old stellar population.
    Preview · Article · Oct 2015 · Publications- Astronomical Society of Japan
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    ABSTRACT: We report on Suzaku results concerning Kes 17, a Galactic mixed-morphology supernova remnant. The X-ray spectrum of the whole Kes 17 is well explained by a pure thermal plasma, in which we found Lyα of Al xiii and Heα of Al xii, Ar xvii, and Ca xix lines for the first time. The abundance pattern and the plasma mass suggest that Kes 17 is a remnant of a core-collapsed supernova of a 25–30 M⊙ progenitor star. The X-ray spectrum of the north region is expressed by a recombining plasma. The origin would be due to the cooling of electrons by thermal conduction to molecular clouds located near the north region.
    No preview · Article · Oct 2015 · Publications- Astronomical Society of Japan
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    ABSTRACT: We have been developing X-ray SOIPIXs for next-generation satellites for X-ray astronomy. Their high time resolution ($\sim10~\mu$s) and event-trigger-output function enable us to read out without pile-ups and to use anti-coincidence systems. Their performance in imaging spectroscopy is comparable to that in the CCDs. A problem in our previous model was degradation of charge-collection efficiency (CCE) at pixel borders. We measured the response in the sub-pixel scale, using finely collimated X-ray beams at $10~\mu$m\Phi$ at SPring-8, and investigated the non-uniformity of the CCE within a pixel. We found that the X-ray detection efficiency and CCE degrade in the sensor region under the pixel circuitry placed outside the buried p-wells (BPW). A 2D simulation of the electric fields shows that the isolated pixel-circuitry outside the BPW creates local minimums in the electric potentials at the interface between the sensor and buried oxide layers. Thus, a part of signal charge is trapped there and is not collected to the BPW. Based on this result, we modified the placement of the in-pixel circuitry so that the electric fields would converge toward the BPW. We confirmed that the CCE at pixel borders is successfully improved with the updated model.
    No preview · Article · Sep 2015
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    ABSTRACT: We have been developing X-ray SOIPIXs, "XRPIX", for future X-ray astronomy satellites. XRPIX is equipped with a function of "event-driven readout", which allows us to readout signal hit pixels only and realizes a high time resolution ($\sim10\mu{\rm s}$). The current version of XRPIX suffers a problem that the readout noise in the event-driven readout mode is higher than that in the the frame readout mode, in which all the pixels are read out serially. Previous studies have clarified that the problem is caused by the cross-talks between buried P-wells (BPW) in the sensor layer and in-pixel circuits in the circuit layer. Thus, we developed new XRPIX having a Double SOI wafer (DSOI), which has an additional silicon layer (middle silicon) working as an electrical shield between the BPW and the in-pixel circuits. After adjusting the voltage applied to the middle silicon, we confirmed the reduction of the cross-talk by observing the analog waveform of the pixel circuit. We also successfully detected $^{241}$Am X-rays with XRPIX.
    No preview · Article · Aug 2015
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    ABSTRACT: This paper presents a low-noise wide-dynamic-range pixel design for a high-energy particle detector in astronomical applications. A silicon on insulator (SOI) based detector is used for the detection of wide energy range of high energy particles (mainly for X-ray). The sensor has a thin layer of SOI CMOS readout circuitry and a thick layer of high-resistivity detector vertically stacked in a single chip. Pixel circuits are divided into two parts; signal sensing circuit and event detection circuit. The event detection circuit consisting of a comparator and logic circuits which detect the incidence of high energy particle categorizes the incident photon it into two energy groups using an appropriate energy threshold and generate a two-bit code for an event and energy level. The code for energy level is then used for selection of the gain of the in-pixel amplifier for the detected signal, providing a function of high-dynamic-range signal measurement. The two-bit code for the event and energy level is scanned in the event scanning block and the signals from the hit pixels only are read out. The variable-gain in-pixel amplifier uses a continuous integrator and integration-time control for the variable gain. The proposed design allows the small signal detection and wide dynamic range due to the adaptive gain technique and capability of correlated double sampling (CDS) technique of kTC noise canceling of the charge detector. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    No preview · Conference Paper · Aug 2015
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    ABSTRACT: SOI (Silicon-On-Insulator) pixel sensor is promising technology for developing the high position resolution detector by integrating the small pixels and circuits in the monolithic way. The event driven (trigger mode) SOI based pixel sensor has also been developed for the application of X-ray astronomy with the purpose of reducing the noise using anti-coincidence event. This trigger mode SOI pixel sensor working with in the rate of kilo Hz is also a promising scatter detector for advanced Compton imaging to track the Compton recoiled electrons.
    Full-text · Article · Jul 2015
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    ABSTRACT: We have developed CMOS imaging sensor (XRPIX) using SOI (Silicon-On-Insulator) technology for the X-ray astronomical use. XRPIX(X-Ray soiPIXel) has advantage of a high time resolution, a high position resolution and an observation in a wide X-ray energy band with a thick depletion layer of over 200um. However, the energy resolution of XRPIX is not as good as one of X-ray CCD. Therefore improvement of the the energy resolution is one of the most important development item of XRPIX. In order to evaluate the performance XRPIX more precisely, we have investigated on the temperature dependence of the basic performance, such as readout noise, leak current, gain and energy resolution, using two type of XRPIX, XRPIX1 and XRPIX2b_CZ. In our study, we confirmed the readout noise, the leak current noise and the energy resolution clearly depended on the operating temperature of XRPIX. In addition, we divided the readout noise into the leak current noise and the circuit origin noise. As a result, we found that noise of the electronic circuitry origin was proportional to the square root of operating temperature.
    Preview · Article · Jul 2015
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    ABSTRACT: We propose a light dark matter search experiment using an SOI pixel detector (SOIPIX). The event-driven SOIPIX can be a powerful tool for detecting light WIMPs because of its low energy threshold (< 1 keV) and high timing resolution (few {\mu}s). In this study, we evaluate the performance of an SOIPIX prototype detector and we examine the required specifications of SOIPIX for our target sensitivity.
    Preview · Article · Jul 2015
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    ABSTRACT: A low noise and wide dynamic range event driven detector for the detection of X-Ray energy is realized using 0.2 [um] Silicon on insulator (SOI) technology. Pixel circuits are divided into two parts; signal sensing circuit and event detection circuit. Event detection circuit is activated when X-Ray energy falls into the detector. In-pixel gain selection is implemented for the detection of a small signal and wide band of energy particle. Adaptive gain and capability of correlated double sampling (CDS) technique for the kTC noise canceling of charge detector realizes the low noise and high dynamic range event driven detector.
    Full-text · Article · Jul 2015
  • Ayaki Takeda · Takeshi Go Tsuru · Shoji Kawahito
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    ABSTRACT: We have been developing monolithic active pixel sensors series, named ``XRPIX'', based on the silicon-on-insulator (SOI) pixel technology, for future X-ray astronomical satellites. The XRPIX series offers high coincidence time resolution (~?1??s), superior readout time (~?10??s), and a wide energy range (0.5?40 keV) . In the previous study, we successfully demonstrated X-ray detection by event-driven readout of XRPIX2b. We here report recent improvements in spectroscopic performance. We successfully increased the gain and reduced the readout noise in XRPIX2b by decreasing the parasitic capacitance of the sense-node originated in the buried p-well (BPW) . On the other hand, we found significant tail structures in the spectral response due to the loss of the charge collection efficiency when a small BPW is employed. Thus, we increased the gain in XRPIX3b by introducing in-pixel charge sensitive amplifiers instead of having even smaller BPW . We finally achieved the readout noise of 35 e? (rms) and the energy resolution of 320 eV (FWHM) at 6 keV without significant loss of the charge collection efficiency.
    No preview · Article · Jun 2015 · Journal of Instrumentation
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    ABSTRACT: We have been developing a new type of active pixel sensor, referred to as “XRPIX” for future X-ray astronomy satellites on the basis of silicon-on-insulator CMOS technology. The problem on our previous device, XRPIX1b, was degradation of the charge-collection efficiency (CCE) at pixel borders. In order to investigate the non-uniformity of the CCE within a pixel, we measured sub-pixel response with X-ray beams whose diameters are at SPring-8. We found that the X-ray detection efficiency and CCE degrade in the sensor region under the pixel circuitry placed outside the buried p-wells (BPW). A 2D simulation of the electric fields with the semiconductor device simulator HyDeLEOS shows that the isolated pixel circuitry outside the BPW makes local minimums in the electric potentials at the interface between the sensor and buried oxide layers, where a part of charge is trapped and is not collected to the BPW. Based on this result, we modified the placement of the in-pixel circuitry in the next device, XRPIX2b, for the electric fields to be converged toward the BPW, and confirmed that the CCE at pixel borders is successfully improved.
    No preview · Article · May 2015 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: 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.
    Full-text · Article · Dec 2014
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    ABSTRACT: We are developing the Soft X-ray Imager (SXI), a charge-coupled device (CCD) camera system to be deployed onboard the ASTRO-H satellite. Using an engineering model system in which design specifications were the same as those of the flight model, we measured charge transfer inefficiency (CTI) and the effects of charge trailing. The CCD was irradiated with monochromatic X-rays produced by a radio isotope (55Fe) and X-ray generator using alpha particles from 241Am. We used four targets for the X-ray generator: (C2F4)n, SiO2, Ti, and Ge. Since CTI degrades energy resolution, we adopted the charge-injection technique to the SXI. With this technique, injected charges fill traps, and subsequent signal charges are transferred with less loss of charge. However, the charge-injection technique can cause positional variations in gain on the CCD chip. Thus, we constructed a method for correcting CTI. We also evaluated the charge trailing effect and tested a method for correcting its effects. After applying these corrections to charge injection, variations in gain improved from 0.5% to 0.1% over the CCD chip, and the energy resolution (FWHM) improved from to at 5.9 keV.
    No preview · Article · Nov 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: We are developing a monolithic active pixel sensor referred to as XRPIX for X-ray astronomy on the basis of silicon-on-insulator CMOS technology. A crucial issue in our recent development is the impact of incomplete charge collection on the spectroscopic performance. In this paper, we report the spectral responses of several devices having different intra-pixel structures or produced from different wafers. We found that an emission line spectrum exhibits large low-energy tails when the size of the buried p-well, which acts as the charge-collection node, is small. Moreover, in charge sharing events, the peak channels of the emission lines shift toward channels lower than those without charge sharing. This peak shift is more pronounced as the distance between the pixel center and the position of incident photon increases. This suggests that the charge-collection efficiency is degraded at the pixel boundary. We also found that the charge-collection efficiency depends on the strength of the electric field at the interface of the depletion and insulator layers.
    No preview · Article · Nov 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: An elongated X-ray source with a strong K-shell line from He-like iron (Fe XXVI) is found at (RA, Dec)_{J2000.0}=(17h44m00s.0, -29D13'40''.9) in the Galactic center region. The position coincides with the X-ray thread, G359.55+0.16, which is aligned with the radio non-thermal filament. The X-ray spectrum is well fitted with an absorbed thin thermal plasma (apec) model. The best-fit temperature, metal abundance, and column density are 4.1^{+2.7}_{-1.8} keV, 0.58^{+0.41}_{-0.32} solar, and 6.1^{+2.5}_{-1.3}x10^{22} cm^{-2}, respectively. These values are similar to those of the largely extended Galactic center X-ray emission.
    Preview · Article · Sep 2014 · Publications- Astronomical Society of Japan
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    ABSTRACT: We have been developing monolithic active pixel sensors, known as Kyoto's X-ray SOIPIXs, based on the CMOS SOI (silicon-on-insulator) technology for next-generation X-ray astronomy satellites. The event trigger output function implemented in each pixel offers microsecond time resolution and enables reduction of the non-X-ray background that dominates the high X-ray energy band above 5--10 keV. A fully depleted SOI with a thick depletion layer and back illumination offers wide band coverage of 0.3--40 keV. Here, we report recent progress in the X-ray SOIPIX development. In this study, we achieved an energy resolution of 300~eV (FWHM) at 6~keV and a read-out noise of 33~e- (rms) in the frame readout mode, which allows us to clearly resolve Mn-K$\alpha$ and K$\beta$. Moreover, we produced a fully depleted layer with a thickness of $500~{\rm \mu m}$. The event-driven readout mode has already been successfully demonstrated.
    Full-text · Article · Aug 2014 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: X-ray CCD operated onboard satellite are contaminated by outgas from organic material used in satellites. This contamination causes a significant reduction in the detection sensitivity of X-ray detectors. In order to prevent such contamination to the Back-Illuminated CCD (BI-CCD) of the Soft X-ray Imager (SXI) onboard ASTRO-H, we have developed a Contamination Blocking Filter (CBF), which consists of ~30nm thick Aluminum and ~200nm thick Polyimide. The CBF is be placed on the top of the CCD camera hood and is required to have a high X-ray transmission in order to take advantage of the high detection efficiency of BI-CCD. We measured the X-ray transmission of three flight candidates of the CBF last October at the SPring-8 and obtained the X-ray transmission of three CBFs in the soft X-ray energy from 0.2 to 1.8 keV which covers the absorption edges around C-K, N-K, O-K, and Al-K including X-ray absorption fine structure (XAFS). In these measurements, we found three CBFs have high X-ray transmission below 2ke V, e.g. ~70% at around 0.5 keV, and determined the thickness of Al and Polyimide to be 220 nm and ~50 nm, respectively. We will calculate the response function of SXI including these results.
    No preview · Conference Paper · Jul 2014
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    ABSTRACT: We present Suzaku results of the two Galactic supernova remnants (SNRs) G350.1−0.3 and G349.7+0.2. We find Al and Ni Kα lines from both the SNRs for the first time, in addition to previously detected K-shell lines of Mg, Si, S, Ar, Ca, and Fe. The spectra are well described by two optically thin thermal plasmas: a low-temperature (low-kT) plasma in collisional ionization equilibrium and a high-temperature (high-kT) plasma in non-equilibrium ionization. Since the low-kT plasma has solar metal abundances, it is thought to be of interstellar medium origin. The high-kT plasma has super-solar abundances, hence it is likely to be of ejecta origin. The abundance patterns of the ejecta components are similar to those of core-collapse supernovae with progenitor masses of ∼ 15–25 M⊙ for G350.1−0.3 and ∼ 35–40 M⊙ for G349.7+0.2. We find extremely high abundances of Ni compared to Fe (ZNi/ZFe ∼ 8). Based on the measured column densities between the SNRs and the near sky background, we propose that G350.1−0.3 and G349.7+0.2 are located at distances of 9 ± 3 kpc and 12 ± 5 kpc, respectively. Then the ejecta masses are estimated to be ∼ 13 M⊙ and ∼ 24 M⊙ for G350−0.3 and G349.7+0.2, respectively. These values are consistent with the progenitor masses of ∼ 15–25 M⊙ and ∼ 35–40 M⊙ for G350.1−0.3 and G349.7+0.2, respectively.
    Preview · Article · Mar 2014 · Publications- Astronomical Society of Japan
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    ABSTRACT: We present deep observations of the Galactic supernova remnant IC 443 with the Suzaku X-ray satellite. We find prominent K-shell lines from iron and nickel, together with a triangle residual at 8-10 keV, which corresponds to the energy of the radiative recombination continuum (RRC) of He-like iron. In addition, the wavy residuals have been seen at ~5.1 and ~5.5 keV. We confirm that the residuals show the first enhanced RRCs of He- and H-like calcium found in supernova remnants. These facts provide robust evidence for the recombining plasma. We reproduce the plasma in the 3.7-10 keV band using a recombining plasma model at the electron temperature 0.65 keV. The recombination parameter n et (n e is electron density and t is elapsed time after formation of a recombining plasma) and abundances of iron and nickel are strongly correlated, and hence the errors are large. On the other hand, the ratio of nickel to iron relative to the solar abundances is well constrained to 11 (1σ). A possibility is that the large abundance ratio is a result of an asymmetric explosion of the progenitor star.
    Preview · Article · Mar 2014 · The Astrophysical Journal
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    ABSTRACT: We report the detection of a distant star-forming galaxy, ALMA J010748.3?173028, which is identified by a 13? emission line at 99.75?GHz (S?v = 3.1?Jy?km?s?1), behind the nearby merging galaxies VV114 using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3. We also find an 880 ?m counterpart with ALMA Band 7 (S 880?m = 11.2?mJy). A careful comparison of the intensities of the line and the continuum suggests that the line is a redshifted 12CO transition. A photometric redshift analysis using the infrared to radio data favors a CO redshift of z = 2.467, although z = 3.622 is acceptable. We also find a hard X-ray counterpart, suggesting the presence of a luminous (L X ~ 1044?erg?s?1) active galactic nucleus obscured by a large hydrogen column (N H ~ 2 × 1023 cm?2 if z = 2.47). A cosmological simulation shows that the chance detection rate of a CO-emitting galaxy at z > 1 with ≥1?Jy?km?s?1 is ~10?3 per single ALMA field of view and 7.5?GHz bandwidth at 99.75?GHz. This demonstrates that ALMA has sufficient sensitivity to find an emission-line galaxy such as ALMA J010748.3?173028 even by chance, although the likelihood of stumbling across such a source is not high.
    No preview · Article · Jan 2014 · The Astrophysical Journal Letters

Publication Stats

2k Citations
230.41 Total Impact Points

Institutions

  • 1997-2015
    • Kyoto University
      • • Department of Physics II
      • • Division of Physics and Astronomy
      Kioto, Kyoto, Japan
  • 2006
    • HAMAMATSU Photonics K.K.
      Hamamatu, Shizuoka, Japan
  • 2004
    • Japan Aerospace Exploration Agency
      Chōfu, Tōkyō, Japan
  • 1999
    • Osaka University
      • Department of Earth and Space Science
      Suika, Ōsaka, Japan
  • 1998
    • Niigata University
      • Department of Physics
      Niahi-niigata, Niigata, Japan
  • 1990
    • The University of Tokyo
      • Department of Physics
      Tōkyō, Japan