标题： 来自两个源群体的河外宇宙射线扩散 显示英文标题

标题： Extragalactic cosmic rays diffusing from two populations of sources

摘要： 我们考虑在存在湍流星系际磁场的情况下，用两种不同的河外源群体来解释高于$10^{17}$电子伏特能量的宇宙射线观测谱和成分的可能性（还包括一个逐渐消失的银河系宇宙射线成分）。 这些群体被认为是具有刚度依赖谱的不同核种的叠加。 第一个河外群体在$10^{17}$到$10^{18}$电子伏特的能量范围内占主导地位，它由具有相对较大的密度（$> 10^{-3}$兆秒差距$^{-3}$）和陡峭谱的源组成。 第二个河外群体主导了几个艾电子伏特以上的宇宙射线通量，它的谱指数更平缓，并在几个$Z$艾电子伏特处有一个高能截止（其中$eZ$是相关的宇宙射线电荷）。 这个种群的源密度较低（$<10^{-4}$Mpc$^{-3}$），因此典型的源间距离大于几十Mpc，受到磁视界效应的显著影响，该效应强烈抑制低于$\sim Z$EeV能量的通量。 我们讨论这种情景如何与由扩散冲击加速机制预期产生的宇宙射线源谱指数值相协调。 显示英文摘要

摘要： We consider the possibility of explaining the observed spectrum and composition of the cosmic rays with energies above $10^{17}$ eV in terms of two different extragalactic populations of sources in the presence of a turbulent intergalactic magnetic field (including also a fading Galactic cosmic-ray component). The populations are considered to be the superposition of different nuclear species having rigidity dependent spectra. The first extragalactic population is dominant in the energy range $10^{17}$ to $10^{18}$ eV and consists of sources having a relatively large density ($> 10^{-3}$ Mpc$^{-3}$) and a steep spectrum. The second extragalactic population dominates the cosmic ray flux above few EeV, it has a harder spectral slope and has a high-energy cutoff at few $Z$ EeV (where $eZ$ is the associated cosmic ray charge). This population has a lower density of sources ($<10^{-4}$ Mpc$^{-3}$), so that the typical intersource separation is larger than few tens of Mpc, being significantly affected by a magnetic horizon effect that strongly suppresses its flux for energies below $\sim Z$ EeV. We discuss how this scenario could be reconciled with the values of the cosmic-ray source spectral indices that are expected to result from the diffusive shock acceleration mechanism.