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arXiv 0802.1636astro-ph
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关于伽马射线暴余辉的可变性--向非相对论运动转变的可能性

On the Variability of Gamma-Ray Burst Afterglows - A Possibility of a Transition to Nonrelativistic Motion

R. A. Burenin

摘要:

在许多伽马射线暴余辉中观察到时间尺度δt < t的变化。众所周知,在简单模型的框架内,如果余辉是由外部激波发射的,那么就不应该有这种变化,外部激波是由超相对论性喷出物与周围星际介质相互作用产生的。Ioka等人(2005年)建立了相应的限制,在某些情况下与观测结果不一致。另一方面,如果运动不是相对论性的,那么余辉的快速变化可以更容易地解释。在这方面,我们讨论了伽玛暴源向次相对论运动转变时间的各种估计。我们指出,这种转变应该发生在一个观察到的时间尺度约10天。在周围星际介质密度较高(~ 10 ^2 - 10 ^4 cm^{-3})或密度为\dot M ~ 10^{-5} - 10^{-4} M_(\odot)/年的恒星风的情况下,向亚相对论运动的转变可以在~1天的时间尺度上发生。这些密度很可能在恒星形成区和大质量沃尔夫-拉叶星周围。

英文摘要:

Variability on time scales δt < t is observed in many gamma-ray burst afterglows. It is well known that there should be no such variability if the afterglow is emitted by external shock, which is produced by the interaction of ultrarelativistic ejecta with the ambient interstellar medium, within the framework of simple models. The corresponding constraints were established by Ioka et al. (2005) and in some cases are inconsistent with observations. On the other hand, if the motion is not relativistic, then the fast variability of the afterglow can be explained much more easily. In this connection we discuss various estimates of the time of the transition to subrelativistic motion in GRB source. We point out, that this transition should occur on an observed time scale of ~10 days. In the case of a higher density of the ambient interstellar medium ~10^2-10^4 cm^{-3} or dense stellar wind with \dot M ~ 10^{-5} - 10^{-4} M_\odot/year the transition to a subrelativistic motion can occur on a time scale of ~1 day. These densities may well be expected in star-forming regions and around massive Wolf-Rayet stars.

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