Spectral Evolution of GRB060904A Observed with Swift and Suzaku- Possibility of Inefficient Electron Acceleration-猫眼课题宝

DOI：

10.1093/pasj/60.sp1.s351

发表时间：

2007-08

期刊：

Publications of the Astronomical Society of Japan

影响因子：

2.3

通讯作者：

中科院分区：

物理与天体物理4区

文献类型：

作者：

D. Yonetoku;S. Tanabe;T. Murakami;N. Emura;Y. Aoyama;T. Kidamura;H. Kodaira;Y. Kodama;R. Kozaka;T. Nashimoto;S. Okuno;S. Yokota;S. Yoshinari;K. Abe;K. Onda;M. Tashiro;Y. Urata;Y. Nakagawa;S. Sugita;K. Yamaoka;A. Yoshida;T. Ishimura;N. Kawai;T. Shimokawabe;K. Kinugasa;T. Kohmura;K. Kubota;K. Sugiyasu;Y. Ueda;K. Masui;K. Nakazawa;Tadayuki Takahashi;S. Maeno;E. Sonoda;M. Yamauchi;M. Kuwahara;T. Tamagawa;D. Matsuura;Motoko Suzuki;S. Barthelmy;N. Gehrels;J. Nousek

我们用雨燕和朱雀卫星观测到GRB 060904 A的X射线余辉。我们发现在BAT和XRT数据中，X射线耀斑的快速尾部阶段和下降阶段都有快速的光谱软化。用幂律光子指数拟合观测到的光谱，在瞬发尾，幂律光子指数在几百秒内从$\Gamma = 1.51^{+0.04}-0.03}$迅速变化到$\Gamma = 5.30^{+0.69}-0.59}$。这是有史以来观测到的最陡峭的X射线光谱之一，使得它很难用简单的电子加速和同步辐射来解释。然后，我们应用了另一种光谱拟合使用一个破碎的幂律指数截止（BPEC）模型。考虑截止能量与能量分布中最大能量电子的同步频率相等的情况是有效的。由于谱截止出现在软X射线波段，我们得出结论，电子加速已在GRB 060904 A的内部冲击无效。这些截止谱在瞬发尾相到浅衰变相的跃迁时刻突然消失。在此之后，典型的余辉光谱与光子指数为2.0的连续和精确的监测XRT和朱雀/XIS长达1天，因为突发触发时间。我们可以成功地追踪两个特征断裂能（峰值能量和截止能量）的时间历史，它们显示出$propto t^{-3} sim t^{-4}$的时间依赖性，而随后的余辉光谱是相当稳定的。这一事实表明，瞬发尾的发射物质是由于完全不同的动力学从浅衰变成分。因此，我们得出结论，两种不同现象的发射位点明显不同。

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.

Spectral Evolution of GRB060904A Observed with Swift and Suzaku- Possibility of Inefficient Electron Acceleration

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