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arXiv 0807.3442astro-ph
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超高能宇宙射线的到达分布对源的启示

Implications to Sources of Ultra-high-energy Cosmic Rays from their Arrival Distribution

Hajime Takami, Katsuhiko Sato

摘要:

基于超高能宇宙射线(UHECR)源到达方向分布的统计特征,估算了UHECR源的局域数密度。我们计算了$10^{19}$ eV以上质子在银河系磁场和结构化星系际磁场中的到达分布,并与Pierre Auger天文台的观测结果进行了统计比较。在最高能量的到达分布中的各向异性使我们能够估计UHECR源的数密度为$\sim 10^{-4} {\rm Mpc}^{-3}$,假设UHECR源的持续活动。我们比较估计的数密度的UHECR源与已知的天体物理对象的数密度。这个估计的数密度与Fanaroff-Reily I星系的数密度是一致的。我们还讨论了在$10^{19}$ eV以上的到达分布中观察到的{ \it各向同性}的再现性。我们发现,估计的源模型不能再现所观察到的各向同性。然而,观察到的各向同性可以用$10^{-2}$ - $10^{-3} {\rm Mpc}^{-3}$的数密度重现。这一事实表明存在最大加速能量为$\sim 10^{19}$ eV的UHECR源,其数密度比注入最高能量宇宙射线的数密度高一个数量级。

英文摘要:

We estimate the local number density of sources of ultra-high-energy cosmic rays (UHECRs) based on the statistical features of their arrival direction distribution. We calculate the arrival distributions of protons above $10^{19}$ eV taking into account their propagation process in the Galactic magnetic field and a structured intergalactic magnetic field, and statistically compare those with the observational result of the Pierre Auger Observatory. The anisotropy in the arrival distribution at the highest energies enables us to estimate the number density of UHECR sources as $\sim 10^{-4} {\rm Mpc}^{-3}$ assuming the persistent activity of UHECR sources. We compare the estimated number density of UHECR sources with the number densities of known astrophysical objects. This estimated number density is consistent with the number density of Fanaroff-Reily I galaxies. We also discuss the reproducability of the observed {\it isotropy} in the arrival distribution above $10^{19}$ eV. We find that the estimated source model cannot reproduce the observed isotropy. However, the observed isotropy can be reproduced with the number density of $10^{-2}$-$10^{-3} {\rm Mpc}^{-3}$. This fact indicates the existence of UHECR sources with a maximum acceleration energy of $\sim 10^{19}$ eV whose number density is an order of magnitude more than that injecting the highest energy cosmic rays.

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