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arXiv 1509.01367astro-ph.HEastro-ph.CO
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星系团的中微子与射电约束

Neutrinos from Clusters of Galaxies and Radio Constraints

Fabio Zandanel, Irene Tamborra, Stefano Gabici, Shin'ichiro Ando

摘要:

宇宙射线(CR)质子可以在星系团中积累宇宙时间。它们与团簇内介质(ICM)的质子发生强子相互作用,产生次级电子、γ射线和高能中微子。根据冰立方天文台最近发现的高能中微子事件,我们估计了星系团对弥散γ射线和中微子背景的贡献。这是第一次,我们始终考虑到同步辐射产生的次级电子,并要求集群无线电计数得到尊重。对于一个选择的参数尊重当前的限制,从无线电到伽马射线,并假设质子光谱指数为-2,我们发现,强子相互作用在集群中的贡献不到10%的冰立方流量,和更少的总河外伽马射线背景费米观察到。对于光谱指数<-2,它们所占的比例不到1%。冰立方观测到的高能中微子流只有在采用一个非常硬的(和推测的)谱指数>-2的情况下才能在不违反射电约束的情况下再现。然而,这种情况与高能IceCube数据相矛盾,IceCube数据似乎表明中微子通量的光谱能量分布随着粒子能量的减少而减少。我们强调,我们的结果是有效的所有类型的源注入CR质子到ICM,而冰立方可以测试最乐观的情况下,光谱指数>=-2.2附近的几个大质量物体堆叠,星系团不能给任何相关的贡献河外伽玛射线和中微子背景在任何现实的情况下。

英文摘要:

Cosmic-ray (CR) protons can accumulate for cosmological times in clusters of galaxies. Their hadronic interactions with protons of the intra-cluster medium (ICM) generate secondary electrons, gamma-rays and high-energy neutrinos. In light of the high-energy neutrino events recently discovered by the IceCube observatory, we estimate the contribution from galaxy clusters to the diffuse gamma-ray and neutrino backgrounds. For the first time, we consistently take into account the synchrotron emission generated by secondary electrons and require the clusters radio counts to be respected. For a choice of parameters respecting current constraints from radio to gamma-rays, and assuming a proton spectral index of -2, we find that hadronic interactions in clusters contribute by less than 10% to the IceCube flux, and much less to the total extragalactic gamma-ray background observed by Fermi. They account for less than 1% for spectral indexes <-2. The high-energy neutrino flux observed by IceCube can be reproduced without violating radio constraints only if a very hard (and speculative) spectral index >-2 is adopted. However, this scenario is in tension with the high-energy IceCube data, which seem to suggest a spectral energy distribution of the neutrino flux that decreases with the particle energy. We stress that our results are valid for all kind of sources injecting CR protons into the ICM, and that, while IceCube can test the most optimistic scenarios for spectral indexes >=-2.2 by stacking few nearby massive objects, clusters of galaxies cannot give any relevant contribution to the extragalactic gamma-ray and neutrino backgrounds in any realistic scenario.

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