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GRB X射线余辉浅衰变阶段高能发射的观测特征

Observational Signatures of High-Energy Emission during the Shallow Decay Phase of GRB X-Ray Afterglows

Y. W. Yu, X. W. Liu, Z. G. Dai

备注：
22 pages, 7 figures, accepted for publication in ApJ
发表信息：
Astrophys.J.671:637-644,2007
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摘要：

伽马射线暴（GRB）中广泛存在的X射线余辉的浅衰减相被普遍认为是由于长时间的能量注入。携带注入能量的外流，根据能量占主导地位的成分，分为两种可能的类型：重子主导和轻子主导。前一种外流可能是在伽玛暴的瞬发阶段喷出的喷出物，由一系列分布有洛伦兹因子的重子壳层组成，后一种外流可能是由爆发后中心引擎驱动的电子-正电子对风。本文对基于这两种能量注入的火球动力学提供了统一的描述，并考虑电子的同步辐射和逆康普顿散射（包括同步辐射自康普顿散射和组合逆康普顿散射）计算了相应的高能光子发射。我们发现，在这两种能量注入模型中，在X射线浅衰变阶段，高能光变曲线有一个平台（甚至是一个驼峰）。特别是，在轻子主导的模型中，相当大一部分的注入能量可以被持久的反向冲击所分享，因为它是相对论性的。此外，几乎所有的反激波能量都由轻子携带，因此反康普顿辐射显著增强。因此，这个模型预测更显着的高能余辉发射比重子占主导地位的模型。我们认为，这些观测签名将被用来区分不同的能量注入模型在即将到来的{ \em伽马射线大面积空间望远镜}（GLAST）时代。

英文摘要：

The widely existing shallow decay phase of the X-ray afterglows of gamma-ray bursts (GRBs) is generally accepted to be due to long-lasting energy injection. The outflows carrying the injecting energy, based on the component that is dominative in energy, fall into two possible types: baryon-dominated and lepton-dominated ones. The former type of outflow could be ejecta that is ejected during the prompt phase of a GRB and consists of a series of baryonic shells with a distribution of Lorentz factors, and the latter type could be an electron-positron-pair wind that is driven by the post-burst central engine. We here provide a unified description for the dynamics of fireballs based on these two types of energy injection, and calculate the corresponding high-energy photon emission by considering synchrotron radiation and inverse Compton scattering (including synchrotron self-Compton and combined inverse-Compton) of electrons. We find that, in the two energy-injection models, there is a plateau (even a hump) in high-energy light curves during the X-ray shallow decay phase. In particular, a considerable fraction of the injecting energy in the lepton-dominated model can be shared by the long-lasting reverse shock since it is relativistic. Furthermore, almost all of the energy of the reverse shock is carried by leptons, and thus the inverse-Compton emission is enhanced dramatically. Therefore, this model predicts more significant high-energy afterglow emission than the baryon-dominated model. We argue that these observational signatures would be used to discriminate between different energy-injection models in the upcoming {\em Gamma-ray Large Area Space Telescope} (GLAST) era.

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