任意磁化的GRB喷出物的减速：完全演化
Deceleration of arbitrarily magnetized GRB ejecta: the complete evolution
摘要：
我们的目标是定量地了解伽玛暴喷出物的动力学效应和观测特征的磁化余辉的开始。我们进行超高分辨率一维相对论MHD模拟的相互作用的径向膨胀，磁化喷出物与星际介质。由于喷出物与环爆介质相互作用区域的极端跳跃条件，需要高分辨率的数值解。我们研究了超相对论壳层的演化过程，一直到自相似渐近相。我们的模拟表明，完整的演化可以用两个参数来表征，即Sari和Piran（1995）引入的磁化强度σ_0和磁化强度σ_0。我们利用这一性质，通过产生数值模型，其中壳层洛伦兹因子为γ_0 ~ tens，并将结果重新标度为任意大的γ_0。我们发现，对于σ_0 >~ 1的喷出物，其逆激波通常很弱或不存在。前向激波发射的起始受到磁化强度的强烈影响。另一方面，壳层的磁能在短时间内（约为爆发持续时间的几倍）转移到外部介质。后来的前向激波发射不包含流的初始磁化的信息。强磁化壳层在经历了一个实质性的减速之后，其渐近演化与流体动力壳层的渐近演化相似，即，它们完全进入Blandford-McKee自相似区。
英文摘要：
(Abridged) We aim to quantitatively understand the dynamical effect and observational signatures of magnetization of the GRB ejecta on the onset of the afterglow. We perform ultrahigh-resolution one-dimensional relativistic MHD simulations of the interaction of a radially expanding, magnetized ejecta with the interstellar medium. The need of ultrahigh numerical resolution derives from the extreme jump conditions in the region of interaction between the ejecta and the circumburst medium. We study the evolution of an ultrarelativistic shell all the way to a the self-similar asymptotic phase. Our simulations show that the complete evolution can be characterized in terms of two parameters, namely, the ξparameter introduced by Sari & Piran (1995) and the magnetization σ_0. We exploit this property by producing numerical models where the shell Lorentz factor is γ_0 ~ tens and rescaling the results to arbitrarily large γ_0. We find that the reverse shock is typically very weak or absent for ejecta characterized by σ_0 >~ 1. The onset of the forward shock emission is strongly affected by the magnetization. On the other hand, the magnetic energy of the shell is transfered to the external medium on a short timescale (~several times the duration of the burst). The later forward shock emission does not contain information for the initial magnetization of the flow. The asymptotic evolution of strongly magnetized shells, after they have suffred a substantial deceleration, resembles that of hydrodynamic shells, i.e., they fully enter in the Blandford-McKee self-similar regime.
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