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arXiv 1003.3840astro-ph.HE
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大质量快速旋转恒星前身源伽玛暴的静止坐标紫外光谱

The rest-frame ultraviolet spectra of GRBs from massive rapidly-rotating stellar progenitors

Peter B. Robinson, Rosalba Perna, Davide Lazzati, Allard J. van Marle

摘要:

大质量恒星在其最终爆炸前的性质会在其恒星风和终端激波产生的星周介质(CSM)中留下印记。我们进行了一个详细的,全面的计算的平均光度伽马射线暴(GRB)的时间变量和角度依赖的透射光谱的CSM结构中产生的崩溃的20 Msun,快速旋转,Z=0.001祖星爆炸。我们研究的情况下,金属最初是在气相中,以及在其中,他们被严重耗尽成灰尘的情况。我们发现,只有当金属在GRB爆炸前被严重耗尽成尘埃时,来自硅、碳和铁的低电离态的高速线才最初存在于光谱中。然而,这样的线消失的时间尺度上的几分之一秒的爆发观察轴上,几秒钟的爆发看到在高纬度,使他们的观察几乎是不可能的。相反,在所有条件下,在终端冲击中产生的静止帧线都清晰可见。我们的结论是,时间分辨,早期的光谱是不是一个有前途的方式,可以常规研究的伽玛射线暴祖风的属性。以前在伽玛射线暴紫外光谱中检测到的高速特征必须是由于一个物理上不相关的吸收体的叠加,或者是由于一个具有非常不寻常性质的祖星。

英文摘要:

The properties of a massive star prior to its final explosion are imprinted in the circumstellar medium (CSM) created by its wind and termination shock. We perform a detailed, comprehensive calculation of the time-variable and angle-dependent transmission spectra of an average-luminosity Gamma-Ray Burst (GRB) which explodes in the CSM structure produced by the collapse of a 20 Msun, rapidly rotating, Z=0.001 progenitor star. We study both the case in which metals are initially in the gaseous phase, as well as the situation in which they are heavily depleted into dust. We find that high-velocity lines from low-ionization states of silicon, carbon, and iron are initially present in the spectrum only if the metals are heavily depleted into dust prior to the GRB explosion. However, such lines disappear on timescales of a fraction of a second for a burst observed on-axis, and of a few seconds for a burst seen at high-latitude, making their observation virtually impossible. Rest-frame lines produced in the termination shock are instead clearly visible in all conditions. We conclude that time-resolved, early-time spectroscopy is not a promising way in which the properties of the GRB progenitor wind can be routinely studied. Previous detections of high velocity features in GRB UV spectra must have been due either due to a superposition of a physically unrelated absorber or to a progenitor star with very unusual properties.

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