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GRB041006时间分辨谱的多分量分析:伽玛暴软分量性质的线索

Multiple Component Analysis of Time Resolved Spectra of GRB041006: A Clue to the Nature of Underlying Soft Component of GRBs

Yuji Shirasaki, Atsumasa Yoshida, Nobuyuki Kawai, Toru Tamagawa, Takanori Sakamoto, Motoko Suzuki, Yujin Nakagawam, Akina Kobayashi, Satoshi Sugita, Ichiro Taka… 展开作者

Yuji Shirasaki, Atsumasa Yoshida, Nobuyuki Kawai, Toru Tamagawa, Takanori Sakamoto, Motoko Suzuki, Yujin Nakagawam, Akina Kobayashi, Satoshi Sugita, Ichiro Takahashi, Makoto Arimoto, Takashi Shimokawabe, Nicolas Vasquez Pazmino, Takuto Ishimura, Rie Sato, Masaru Matsuoka, Edward E. Fenimore, Mark Galassi, Donald Q. Lamb, Carlo Graziani, Timothy Q. Donaghy, Jean-Luc Atteia, Alexandre Pelangeon, Roland Vanderspek, Geoffrey B. Crew, John P. Doty, Joel Villasenor, Gregory Prigozhin, Nat Butler, George R. Ricker, Kevin Hurley, Stanford E. Woosley, Graziella Pizzichini

摘要:

GRB 041006在2004年10月6日12:18:08 UT被HETE-2探测到。这个伽玛射线暴显示出软X射线辐射,这是主事件发生前的前兆,也是主峰结束后的软X射线尾。四个不同能带的光变曲线显示出不同的特征,在较高的能带处,光变曲线中出现多个峰,而在较低的能带处,一个较宽的凸起占主导地位。预计这些不同的特征是几种组分的混合物的结果,其中每种组分具有不同的能量学和可变性。为了揭示每个组分的性质,我们分析了时间分辨光谱,并成功地将它们分解为几个组分。我们还发现,这些组件可以分为两个不同的类;一个是一个组件,具有指数衰减的$E_{p}$的特征时间尺度短于$\sim$ 30秒,它的频谱是很好地代表了一个破碎的幂律函数,这是经常观察到的许多提示伽玛射线暴的排放,所以它应该有一个内部冲击的起源。另一种是其$E_{p}$几乎不变且特征时标长于$\sim$ 60秒的组分,并且显示出非常软的发射和较慢的可变性。软分量的光谱的特征在于由打破幂律或黑体光谱。这一分量可能来源于一个相对较宽和较低速度的喷流或火球的光球。通过假设软分量是热发射,辐射半径最初是$4.4 \times 10^{6}$ km,这是蓝超巨星的典型半径,在源坐标系中它的膨胀速度是$2.4 \times 10^{5}$ km/s。

英文摘要:

GRB 041006 was detected by HETE-2 at 12:18:08 UT on 06 October 2004. This GRB displays a soft X-ray emission, a precursor before the onset of the main event, and also a soft X-ray tail after the end of the main peak. The light curves in four different energy bands display different features; At higher energy bands several peaks are seen in the light curve, while at lower energy bands a single broader bump dominates. It is expected that these different features are the result of a mixture of several components each of which has different energetics and variability. To reveal the nature of each component, we analysed the time resolved spectra and they are successfully resolved into several components. We also found that these components can be classified into two distinct classes; One is a component which has an exponential decay of $E_{p}$ with a characteristic timescale shorter than $\sim$ 30 sec, and its spectrum is well represented by a broken power law function, which is frequently observed in many prompt GRB emissions, so it should have an internal-shock origin. Another is a component whose $E_{p}$ is almost unchanged with characteristic timescale longer than $\sim$ 60 sec, and shows a very soft emission and slower variability. The spectrum of the soft component is characterized by either a broken power law or a black body spectrum. This component might originate from a relatively wider and lower velocity jet or a photosphere of the fireball. By assuming that the soft component is a thermal emission, the radiation radius is initially $4.4 \times 10^{6}$ km, which is a typical radius of a blue supergiant, and its expansion velocity is $2.4 \times 10^{5}$ km/s in the source frame.

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