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arXiv 1706.02534astro-ph.HE
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UHECR焊剂的各向同性程度如何?

How isotropic can the UHECR flux be?

Armando di Matteo, Peter Tinyakov

摘要:

现代的超高能宇宙射线(UHECR)观测站已经收集到超过10^4个能量超过10 EeV的事件,这些事件的到达方向似乎几乎是各向同性分布的。另一方面,物质在附近宇宙中的分布--因此,据推测也是UHECR源的分布--是不均匀的。尽管宇宙磁场的偏转可能会混淆图像,但这有望在UHECR到达方向的角分布上留下印记。在这项工作中,我们定量研究这种明显的不一致。为此,我们研究的观测值敏感的UHECR源的不均匀性,但强大的不确定性磁场和UHECR的质量组成。我们表明,在一个相当独立的模型的方式,如果源分布跟踪整体的物质分布,在30 EeV以上的能量的到达方向应该表现出相当大的偶极子和四极各向异性,可检测的UHECR天文台在不久的将来。如果不是这样的话,人们将不得不认真地重新考虑目前对宇宙磁场和/或UHECR组成的理解。此外,我们表明,缺乏一个强大的四极矩超过10 EeV的电流数据已经不利于纯质子的组成,并在不久的将来的偶极子和四极矩超过60 EeV的测量将能够提供证据,在这些能量的UHECR质量组成。

英文摘要:

Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 10^4 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed. On the other hand, the distribution of matter in the nearby Universe -- and, therefore, presumably also that of UHECR sources -- is not homogeneous. This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture. In this work, we investigate quantitatively this apparent inconsistency. To this end we study observables sensitive to UHECR source inhomogeneities but robust to uncertainties on magnetic fields and the UHECR mass composition. We show, in a rather model-independent way, that if the source distribution tracks the overall matter distribution, the arrival directions at energies above 30 EeV should exhibit a sizeable dipole and quadrupole anisotropy, detectable by UHECR observatories in the very near future. Were it not the case, one would have to seriously reconsider the present understanding of cosmic magnetic fields and/or the UHECR composition. Also, we show that the lack of a strong quadrupole moment above 10 EeV in the current data already disfavours a pure proton composition, and that in the very near future measurements of the dipole and quadrupole moment above 60 EeV will be able to provide evidence about the UHECR mass composition at those energies.

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。

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