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arXiv 1108.2135astro-ph.HE
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超高能银河系宇宙射线的起源:各向同性问题

Origin of Ultrahigh Energy Galactic Cosmic Rays: The Isotropy Problem

Martin Pohl, David Eichler

摘要:

我们研究了超高能宇宙射线(UHECR)在银河系中的传播,集中在脚踝以下的能量范围在4 EeV的频谱。基于随时间变化的扩散问题的解析解,采用Monte-Carlo方法,通过将源放置在随机位置来计算不连续性。假设一个源人口的规模与重子质量密度或恒星形成(如长GRB),我们得到的约束所产生的不稳定性和观测限制的组成和各向异性。结果表明,在1 e18 eV的组成和各向异性是难以再现的,并要求a)粒子平均自由程远小于回转半径,这意味着逃逸时间很长,b)组成比最近的俄歇数据所建议的要重,c)超高能亚踝分量主要是河外的,或者d)我们生活在超高能宇宙射线产生的一个罕见的平静期,目前的超高能宇宙射线强度远远低于银河系的平均时间。因此,我们建议一个强有力的观测重点,以确定UHECR组成约1 e18 eV。

英文摘要:

We study the propagation of ultra-high-energy cosmic rays (UHECR) in the Galaxy, concentrating on the energy range below the ankle in the spectrum at 4 EeV. A Monte-Carlo method, based on analytical solutions to the time-dependent diffusion problem, is used to account for intermittency by placing sources at random locations. Assuming a source population that scales with baryon mass density or star formation (e.g. long GRB), we derive constraints arising from intermittency and the observational limits on the composition and anisotropy. It is shown that the composition and anisotropy at 1e18 eV are difficult to reproduce and require that either a) the particle mean free path is much smaller than a gyroradius, implying the escape time is very long, b) the composition is heavier than suggested by recent Auger data, c) the ultrahigh-energy sub-ankle component is mostly extragalactic, or d) we are living in a rare lull in the ultrahigh-energy cosmic-ray production, and the current ultrahigh-energy cosmic-ray intensity is far below the Galactic time average. We therefore recommend a strong observational focus on determining the UHECR composition around 1e18 eV.

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