Publications (6)2.44 Total impact
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Article: Current Status of the Suzaku Wide‐band All‐sky Monitor (WAM)
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ABSTRACT: The Suzaku Wide‐band All‐sky Monitor (WAM) consists of 20 BGO anti‐coincidence scintillators for the Hard X‐ray Detector (HXD). The WAM has a wide field of view (FOV), about half of the whole sky, a large collecting area, 800 cm2, and broad‐band energy coverage from 50 to 5000 keV. Thus it has been designed to work as a gamma‐ray burst detector. For the three years since Suzaku launch in July 2005, the WAM has been working very well. About 500 GRBs have been detected through the end of 2008, corresponding to a detection rate of ∼ 140 GRBs per year. The current status of the WAM is presented in this paper.AIP Conference Proceedings. 05/2009; 1133(1):91-93. -
Article: Design and In-Orbit Performance of the Suzaku Wide-Band All-Sky Monitor
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ABSTRACT: The Suzaku Wide-band All-sky Monitor (WAM) consists of thick BGO anti-coincidence shields of the Hard X-ray Detectors (HXD). It views about half of the sky and has a geometrical area of 800cm2 per side and an effective area of 400cm2, even at 1MeV. Hence, the WAM can provide unique opportunities to detect high-energy emission from GRBs and solar flares in the sub-MeV toMeV range. The WAM has detected more than 400GRBs and 100 solar flares since its launch. This paper describes the in-flight performance of the HXD/WAM during the initial two years of operations, including the in-flight energy response, spectral and timing capabilities, and in-orbit background.Publications- Astronomical Society of Japan 12/2008; 61:35. · 2.44 Impact Factor -
Article: Spectral evolution of GRB 060904A observed with Swift and Suzaku -- Possibility of Inefficient Electron Acceleration
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ABSTRACT: We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the BAT and XRT data. The observed spectra were fit by power-law photon indices which rapidly changed from $\Gamma = 1.51^{+0.04}_{-0.03}$ to $\Gamma = 5.30^{+0.69}_{-0.59}$ within a few hundred seconds in the prompt tail. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron acceleration and synchrotron radiation. Then, we applied an alternative spectral fitting using a broken power-law with exponential cutoff (BPEC) model. It is valid to consider the situation that the cutoff energy is equivalent to the synchrotron frequency of the maximum energy electrons in their energy distribution. Since the spectral cutoff appears in the soft X-ray band, we conclude the electron acceleration has been inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the transition time from the prompt tail phase to the shallow decay one. After that, typical afterglow spectra with the photon indices of 2.0 are continuously and preciously monitored by both XRT and Suzaku/XIS up to 1 day since the burst trigger time. We could successfully trace the temporal history of two characteristic break energies (peak energy and cutoff energy) and they show the time dependence of $\propto t^{-3} \sim t^{-4}$ while the following afterglow spectra are quite stable. This fact indicates that the emitting material of prompt tail is due to completely different dynamics from the shallow decay component. Therefore we conclude the emission sites of two distinct phenomena obviously differ from each other.09/2007; -
Article: RIMOTSによるGRB030329可視光残光の観測
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ABSTRACT: Bright gamma-ray burst GRB030329 was detected by HETE-2 at 1l:37:14.67(UT) on 29 March .2003. We got first image of its optical afterglow with RIMOTS at 164 minutes after the burst. The telescope of RIMOTS has 30cm aperture, and its field of view is 43' X43'. Our data shows its magnitude decreases from 13.0±0.2 to 14.2±0.1. This magnitude change can be described by a power-law function of time whose index is 1.0±0.1. These observations are consistent with other observations within the error. This power-law change of magnitude is explained by the model where a jet having nearly light speed expand and collide with interstellar gas decreasing its speed. Our non-filterd data shows that the fading of the afterglow becomes slower at 0.16 day after the burst. This change isn't seen in any data taken with R-band by other observatory. This phenomenon may be due to the flux change of U, B, or V band. The spectroscopic observations are needed for further analysis of this phenomenon. -
Article: RIMOTSによるGRB041006の可視光残光の早期観測
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ABSTRACT: GRB041006 was first detected by HETE-2 on 2004 Oct. 6 at 12:18:08 UT. We have observed it's earliest optical afterglow from 12:19:18 UT to through the night. Our observation was performed by using the unfiltered CCD camera on the 30-cm telescope. We combined our converted R band data with those reported by GCN. Statistics don't allow us to say in detail but the light curve shows two slope changes. The power-low index α of the flux decay is α =0.62 before about 0.0053 day after the burst, α =-0.45 from 0.0053 day to 0.077 day after the burst, and α =-1 after 0.077 day. These index changes can be explained by forward shock in synchrotron shock model. During the first flat period, optical emission is generated by cooling of all electrons, which are accelerated by forward shock. But the speed of the shell become slower, then the critical frequency becomes lower than the optical band. The light curve, therefore, got dark slowly. And finally, since the minimum frequency at which the slowest ones among the accelerated electrons emit is below the optical frequency, the electrons that can emit optical light decrease rapidly. So the afterglow darkened fast. -
Article: ガンマ線バースト可視光残光の光度解析
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ABSTRACT: Abstract GRB041006 is a gamma-ray burst which was originally detected by HETE-2 at 12:18:06 Oct. 6 in 2004. Our 30cm telescope(RIMOTS) has succeeded in observing the optical afterglow of it with unfilterd cooling CCD camera only 70 seconds after the burst. First three images were slightly flowed. Standard method of photometry cannot be applied to these images. We have developed an original method to analyses these images. This method was confirmed to work properly to get the correct magnitude of afterglow. By using this method, it was able to obtain the very early light curve of optical afterglow that there are few observation until now.
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Institutions
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2009
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Miyazaki University
- Department of Applied Physics
Miyazaki-shi, Miyazaki-ken, Japan
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