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arXiv 0705.1108astro-ph
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相对论风泡GRB X射线余辉的浅衰变相

Shallow decay phase of GRB X-ray afterglows from relativistic wind bubbles

Yun-Wei Yu, Zi-Gao Dai

备注：
5 pages, 4 figures, Accepted for Publication in A&A
发表信息：
Astron.Astrophys.470:119,2007
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摘要：

GRB的爆发后物体很可能是一个高度磁化的，快速旋转的致密物体（例如，毫秒磁星），它可以产生超相对论性的电子-正电子对风。这种风与爆炸期间喷出的向外膨胀的火球相互作用，导致相对论风泡（RWB）。我们数值计算了RWBs的动力学和辐射特性，并利用这个模型解释了Swift观测到的早期X射线余辉的浅衰变相。我们发现，RWB可以分为两种类型：正向冲击为主的泡沫和反向冲击为主的泡沫。它们在$\sim 10^{2}-10^{5}$秒期间的辐射分别由冲击介质和冲击风主导，基于冲击材料的不同磁能分数。对于这两种类型，产生的光变曲线总是有一个浅的衰减阶段。此外，我们提供了一个例子，适合的X射线余辉的GRB 060813和GRB 060814，并表明它们可以产生的前向冲击为主和反向冲击为主的气泡，分别。这意味着，对于一些早期的余辉（例如，GRB 060814），长时间的反向冲击辐射足以解释它们的浅衰变阶段。

英文摘要：

The postburst object of a GRB is likely to be a highly magnetized, rapidly rotating compact object (e.g., a millisecond magnetar), which could produce an ultrarelativistic electron-positron-pair wind. The interaction of such a wind with an outwardly expanding fireball ejected during the burst leads to a relativistic wind bubble (RWB). We numerically calculate the dynamics and radiative properties of RWBs and use this model to explain the shallow decay phase of the early X-ray afterglows observed by Swift. We find that RWBs can fall into two types: forward-shock-dominated and reverse-shock-dominated bubbles. Their radiation during a period of $\sim 10^{2}-10^{5}$ seconds is dominated by the shocked medium and the shocked wind, respectively, based on different magnetic energy fractions of the shocked materials. For both types, the resulting light curves always have a shallow decay phase. In addition, we provide an example fit to the X-ray afterglows of GRB 060813 and GRB 060814 and show that they could be produced by forward-shock-dominated and reverse-shock-dominated bubbles, respectively. This implies that, for some early afterglows (e.g., GRB 060814), the long-lasting reverse shock emission is strong enough to explain their shallow decay phase.

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