arXiv 0804.21752008-04-14astro-ph

伽马射线暴早期X射线余辉发射的全曲率效应

The full curvature effect expected in early X-ray afterglow emission of gamma-ray bursts

Y. -P. Qin

备注：: 28 pages, 9 figures. Accepted for publication in ApJ
发表信息：: Astrophys.J. 683 (2008) 900-912
DOI：: 10.1086/589277

摘要：

研究了在本征辐射谱为幂律谱的情况下，全曲率效应对伽马射线暴（GRB）早期X射线余辉通量的影响。我们发现，众所周知的$t^{-(2+β)}$曲线是目前只有当本征发射是非常短的或发射来自指数冷却。该曲线的时间尺度与洛伦兹因子无关。当本征发射具有幂律光谱和具有无限持续时间的时间幂律分布时，所得的光变曲线将包含两个阶段。第一阶段是快速衰减阶段，其中光变曲线很好地遵循$t^{-(2+β)}$曲线。第二阶段为浅衰减阶段，光变曲线的幂律指数明显小于第一阶段。浅相的开始受到火球半径的严格限制，这反过来又可以对后者施加下限。在时间幂律发射持续有限时间间隔的情况下，在$t^{-(2+β)}$曲线和浅衰减阶段之后将存在第三阶段，其比浅阶段陡得多。作为应用的一个例子，我们用我们的模型拟合了GRB 050219A的XRT数据，并表明曲率效应可以粗略地解释这次爆发。尽管由于拟合的各种选择而不能唯一地确定拟合参数，但是可以估计该爆发的火球半径的下限，其为$\sim 10^{14}cm$。

英文摘要：

We explore the influence of the full curvature effect on the flux of early X-ray afterglow of gamma-ray bursts (GRBs) in cases when the spectrum of the intrinsic emission is a power-law. We find that the well-known $t^{-(2+β)}$ curve is present only when the intrinsic emission is extremely short or the emission arises from an exponential cooling. The time scale of this curve is independent of the Lorentz factor. The resulting light curve would contain two phases when the intrinsic emission has a power-law spectrum and a temporal power-law profile with infinite duration. The first phase is a rapid decay one where the light curve well follows the $t^{-(2+β)}$ curve. The second is a shallow decay phase where the power-law index of the light curve is obviously smaller than that in the first phase. The start of the shallow phase is strictly constrained by the fireball radius, which in turn, can put a lower limit to the latter. In the case when the temporal power-law emission lasts a limited interval of time, there will be a third phase after the $t^{-(2+β)}$ curve and the shallow decay phase, which is much steeper than the shallow phase. As an example of application, we fit the XRT data of GRB 050219A with our model and show that the curvature effect alone can roughly account for this burst. Although fitting parameters can not be uniquely determined due to various choices of fitting, a lower limit of the fireball radius of this burst can be estimated, which is $\sim 10^{14}cm$.

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