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arXiv 1506.03087astro-ph.HE
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相对论激波中电子和离子的加速及其在GRB余辉中的应用

Electron and Ion Acceleration in Relativistic Shocks with Applications to GRB Afterglows

Donald C. Warren, Donald C. Ellison, Andrei M. Bykov, Shiu-Hang Lee

摘要:

我们用相对论激波模拟了质子、电子和氦核的同时一阶费米激波加速。通过参数化粒子扩散,我们的稳态蒙特卡罗模拟允许我们跟踪粒子从非热热能的粒子注入到PeV以上的能量,包括由于宇宙射线(CR)背压的激波结构的非线性平滑。我们观察到的质荷比(A/Z)增强效应被认为是发生在有效的费米加速在非相对论冲击,我们parameterized在粒子在细胞(PIC)模拟中看到的离子能量转移到电子。对于一组给定的环境和模型参数,蒙特卡罗模拟确定粒子分布的绝对标准化,并在很大程度上自洽的方式产生的同步加速器,逆康普顿和π介子衰变发射。该模拟是灵活的,可以很容易地使用广泛的参数典型的伽马射线暴(GRB)余辉。我们描述了不同洛伦兹因子的冲击光子发射的一些初步结果,并概述了蒙特卡罗模拟如何可以推广和耦合到GRB爆炸波的流体动力学模拟。为了简单起见,我们假设玻姆扩散,但强调我们描述的非线性效应主要来自于一个扩展的冲击前兆,其中更高能量的粒子扩散进一步上游。不同的扩散模型,特别是对于最大CR能量和光子发射,会出现定量差异,但只要散射平均自由程是动量的递增函数,这些非线性效应在定性上应该是相似的。

英文摘要:

We have modeled the simultaneous first-order Fermi shock acceleration of protons, electrons, and helium nuclei by relativistic shocks. By parameterizing the particle diffusion, our steady-state Monte Carlo simulation allows us to follow particles from particle injection at nonthermal thermal energies to above PeV energies, including the nonlinear smoothing of the shock structure due to cosmic-ray (CR) backpressure. We observe the mass-to-charge (A/Z) enhancement effect believed to occur in efficient Fermi acceleration in non-relativistic shocks and we parameterize the transfer of ion energy to electrons seen in particle-in-cell (PIC) simulations. For a given set of environmental and model parameters, the Monte Carlo simulation determines the absolute normalization of the particle distributions and the resulting synchrotron, inverse-Compton, and pion-decay emission in a largely self-consistent manner. The simulation is flexible and can be readily used with a wide range of parameters typical of gamma-ray burst (GRB) afterglows. We describe some preliminary results for photon emission from shocks of different Lorentz factors and outline how the Monte Carlo simulation can be generalized and coupled to hydrodynamic simulations of GRB blast waves. We assume Bohm diffusion for simplicity but emphasize that the nonlinear effects we describe stem mainly from an extended shock precursor where higher energy particles diffuse further upstream. Quantitative differences will occur with different diffusion models, particularly for the maximum CR energy and photon emission, but these nonlinear effects should be qualitatively similar as long as the scattering mean free path is an increasing function of momentum.

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