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arXiv 0705.4453astro-ph
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相对论冲击下UHECR产生中一阶费米过程的无效性

The inefficiency of the first-order Fermi process in UHECR production at relativistic shocks

Jacek Niemiec, Michal Ostrowski, Martin Pohl

摘要:

超高能宇宙射线在相对论冲击波中的起源问题是根据最近对一阶费米粒子加速的Monte Carlo研究结果进行讨论的(Niemiec & Ostrowski 2006,Niemiec et al. 2006)。在这些模拟中考虑的冲击附近的湍流磁场的模型,包括在冲击,这使我们能够研究所有的场和粒子的运动特性,是重要的宇宙射线加速的扰动磁场结构的现实功能。我们的研究结果表明,附近的冲击,这是一致的冲击跳跃条件的湍流条件,导致大幅修改的加速过程相对于简化模型,产生广泛的幂律能量分布,往往与“通用”的光谱指数。相对论激波基本上总是超光速的,因此它们优先产生陡峭的粒子光谱,其截止值远低于最大散射能量,通常不超过压缩背景等离子体离子的能量。因此,宇宙射线在相对论性冲击波中加速到非常高的能量是低效的,并且这种冲击预计不会成为超高能粒子的来源。

英文摘要:

The question of the origin of ultra-high-energy cosmic rays at relativistic shock waves is discussed in the light of results of recent Monte Carlo studies of the first-order Fermi particle acceleration (Niemiec & Ostrowski 2006, Niemiec et al. 2006). The models of the turbulent magnetic field near the shock considered in these simulations include realistic features of the perturbed magnetic field structures at the shock, which allow us to study all the field and particle motion characteristics that are important for cosmic-ray acceleration. Our results show that turbulent conditions near the shock, that are consistent with the shock jump conditions, lead to substantial modifications of the acceleration process with respect to the simplified models, that produce wide-range power-law energy distributions, often with the "universal" spectral index. Relativistic shocks are essentially always superluminal, and thus they preferentially generate steep particle spectra with cutoffs well below the maximum scattering energy, often not exceeding the energy of the compressed background plasma ions. Thus, cosmic-ray acceleration to very high energies at relativistic shock waves is inefficient, and such shocks are not expected to be the sources of ultra-high-energy particles.

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