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arXiv 0909.1532astro-ph.HEastro-ph.CO
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银河系磁场干扰最高能量宇宙射线与其源的关联吗?

Does Galactic Magnetic Field Disturb the Correlation of the Highest Energy Cosmic Rays with their Sources?

Hajime Takami, Katsuhiko Sato

摘要:

高能宇宙射线的传播轨迹不仅受到星系际磁场的偏转,而且受到银河系磁场的偏转。这些磁场可以削弱HECR到达方向与其源位置之间的正相关性。为了探讨GMF对期望相关性的影响,我们采用几种GMF模型模拟了能量在$6 \times 10^{19}$ eV以上的质子的到达分布,并对模拟中假设的质子与其源之间的相关性进行了检验。还研究了相关信号对GMF模型的依赖性。通过在半个半球中积累$\sim 200$质子可以观察到这种相关性。相关性的正信号被最大化的典型角标度取决于GMF模型的螺旋分量。如果HECR源的数密度$n_s$为$\sim 10^{-4}$ Mpc $^{-3}$,则该角标度对于双对称螺旋(BS)GMF模型为$\sim 5^o$,对于轴对称螺旋(AS)GMF模型为$\sim 7^o$。一个额外的垂直(偶极子)分量的GMF影响这些角度尺度的$0.5^o$-$1^o$。BS模式和AS模式的相关信号之间的差异在北方天空中是突出的。正相关的显著性取决于源分布。在200个质子探测下,在几乎所有具有$n_s = 10^{-4}$ Mpc $^{-3}$的源分布中,与源相关的模拟HECR事件数小于与同一源偶然相关的随机事件数的概率远小于$10^{-3}$($\sim 3σ$),但在AS GMF模型中,源分布的$\sim 10\%$预测的偶然概率大于$10^{-3}$.此外,我们还简要地讨论了GMF对重核占优组分的影响。

英文摘要:

The propagation trajectories of the highest energy cosmic rays (HECRs) are deflected by not only intergalactic magnetic field but also Galactic magnetic field (GMF). These magnetic fields can weaken the positive correlation between the arrival directions of HECRs and the positions of their sources. In order to explore the effect of GMF on the expected correlation, we simulate the arrival distribution of protons with the energy above $6 \times 10^{19}$ eV taking several GMF models into account, and then test the correlation between the protons and their sources assumed in the simulation. The dependence of the correlation signals on GMF models are also investigated. The correlation can be observed by accumulating $\sim 200$ protons in a half hemisphere. Typical angular scale at which the positive signal of the correlation is maximized depends on the spiral component of GMF models. That angular scale is $\sim 5^o$ for bisymmetric spiral (BS) GMF models and $\sim 7^o$ for axisymmetric spiral (AS) GMF models if the number density of HECR sources, $n_s$, is $\sim 10^{-4}$ Mpc$^{-3}$. An additional vertical (dipole) component of GMF affects these angular scale by $0.5^o$ - $1^o$. The difference between the correlation signal for the BS models and that for the AS models is prominent in the northern sky. Significance of the positive correlation depends on source distribution. The probability that the number of simulated HECR events correlating with sources is smaller than the number of random events correlating with the same sources by chance is much less than $10^{-3}$ ($\sim 3σ$) in almost all the source distributions with $n_s = 10^{-4}$ Mpc$^{-3}$ under 200 protons detection, but $\sim 10\%$ of source distributions predicts the chance probability more than $10^{-3}$ in the AS GMF model. In addition, we also briefly discuss the effect of GMF for heavy-nuclei dominated composition.

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