arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1105.4529astro-ph.HE
收藏

来自银河系超新星遗迹的宇宙射线的扩散传播。II:各向异性

Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. II: anisotropy

Pasquale Blasi, Elena Amato

摘要:

我们研究了超新星遗迹时空分布的随机性对地球观测到的宇宙射线各向异性的影响。计算了不同扩散系数D(E)在银河系中的传播。考虑了原子核的传播和扩散。在高能量下,我们假设$D(E)\sim(E/Z)^δ$,其中$δ=1/3$和$δ=0.6$是参考场景。在考虑和不考虑银河系螺旋结构的情况下,根据超新星遗迹的分布模型,模拟了银河系中超新星遗迹的大尺度分布。我们的计算使我们能够确定的贡献,各向异性导致的大规模分布的SNR在银河系和随机分布的最近的遗迹。天真的期望,各向异性振幅缩放为D(E)被证明是一个过度简化,这并不反映在预测的各向异性的任何现实分布的源。各向异性模式的波动主要是由附近的来源,使预测或解释所观察到的各向异性振幅和相位变得几乎不可能。然而,我们发现,非常弱的能量依赖性的各向异性振幅低于$10^{5}$ GeV和在更高的能量上升,可以最好地解释,如果扩散系数是$D(E)\sim E^{1/3}$。更快的扩散,例如使用$δ=0.6$,通常导致极大的各向异性幅度。螺旋结构在各向异性模式的能量依赖性中引入了有趣的趋势,其定性地反映了数据中所见的趋势。对于大值的晕大小,我们发现,各向异性成为主导的大规模的规则结构的源分布,导致确实是一个单调增加的$δ_A$与能量。

英文摘要:

We investigate the effects of stochasticity in the spatial and temporal distribution of supernova remnants on the anisotropy of cosmic rays observed at Earth. The calculations are carried out for different choices of the diffusion coefficient D(E) for propagation in the Galaxy. The propagation and spallation of nuclei are taken into account. At high energies we assume that $D(E)\sim(E/Z)^δ$, with $δ=1/3$ and $δ=0.6$ being the reference scenarios. The large scale distribution of supernova remnants in the Galaxy is modeled following the distribution of pulsars with and without accounting for the spiral structure of the Galaxy. Our calculations allow us to determine the contribution to anisotropy resulting from both the large scale distribution of SNRs in the Galaxy and the random distribution of the nearest remnants. The naive expectation that the anisotropy amplitude scales as D(E) is shown to be an oversimplification which does not reflect in the predicted anisotropy for any realistic distribution of the sources. The fluctuations in the anisotropy pattern are dominated by nearby sources, so that predicting or explaining the observed anisotropy amplitude and phase becomes close to impossible. We find however that the very weak energy dependence of the anisotropy amplitude below $10^{5}$ GeV and the rise at higher energies, can best be explained if the diffusion coefficient is $D(E)\sim E^{1/3}$. Faster diffusion, for instance with $δ=0.6$, leads in general to an exceedingly large anisotropy amplitude. The spiral structure introduces interesting trends in the energy dependence of the anisotropy pattern, which qualitatively reflect the trend seen in the data. For large values of the halo size we find that the anisotropy becomes dominated by the large scale regular structure of the source distribution, leading indeed to a monotonic increase of $δ_A$ with energy.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑