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タイトル
和文: 
英文:Spectral Evolution of GRB060904A Observed with Swift and Suzaku -- Possibility of Inefficient Electron Acceleration 
著者
和文: Yonetoku, D., Tanabe, S., Murakami, T., Emura, N., Aoyama, Y., Kidamura, T., Kodaira, H., Kodama, Y., Kozaka, R., Nashimoto, T., Okuno, S., Yokota, S., Yoshinari, S., Abe, K., Onda, K., Tashiro, M. S., Urata, Y., Nakagawa, Y. E., Sugita, S., Yamaoka, K., Yoshida, A., Ishimura, T., 河合 誠之, Shimokawabe, T., Kinugasa, K., Kohmura, T., Kubota, K., Sugiyasu, K., Ueda, Y., Masui, K., Nakazawa, K., Takahashi, T., Maeno, S., Sonoda, E., Yamauchi, M., Kuwahara, M., Tamagawa, T., Matsuura, D., Suzuki, M., Barthelmy, S., Gehrels, N., Nousek, J..  
英文: Yonetoku, D., Tanabe, S., Murakami, T., Emura, N., Aoyama, Y., Kidamura, T., Kodaira, H., Kodama, Y., Kozaka, R., Nashimoto, T., Okuno, S., Yokota, S., Yoshinari, S., Abe, K., Onda, K., Tashiro, M. S., Urata, Y., Nakagawa, Y. E., Sugita, S., Yamaoka, K., Yoshida, A., Ishimura, T., Kawai, N., Shimokawabe, T., Kinugasa, K., Kohmura, T., Kubota, K., Sugiyasu, K., Ueda, Y., Masui, K., Nakazawa, K., Takahashi, T., Maeno, S., Sonoda, E., Yamauchi, M., Kuwahara, M., Tamagawa, T., Matsuura, D., Suzuki, M., Barthelmy, S., Gehrels, N., Nousek, J..  
言語 English 
掲載誌/書名
和文: 
英文:Publications of the Astronomical Society of Japan 
巻, 号, ページ Vol. 60        pp. S352-S360
出版年月 2008年2月 
出版者
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英文: 
会議名称
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開催地
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DOI https://doi.org/10.1093/pasj/60.sp1.s351
アブストラクト 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.

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