Sagittarius A* as an origin of the Galactic PeV cosmic rays?
Sagittarius A* as an origin of the Galactic PeV cosmic rays?
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DOI：
10.1088/1475-7516/2017/04/037
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发表时间：
2016-03
影响因子：
6.4
通讯作者：
Y. Fujita;K. Murase;S. Kimura
中科院分区：
文献类型：
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作者：
Y. Fujita;K. Murase;S. Kimura
超新星遗迹通常被认为是观测到的PeV宇宙射线（CR）或银河系PeV粒子加速器（“Pevatron”）的来源。在这项工作中，我们研究人马座A*（Sgr A*），这是银河系的低光度活动星系核，作为另一个可能的候选人的Pevatron，因为它有时变得非常活跃的过去。我们假设在大约107年前的爆发中，当费米泡产生时，Sgr A* 注入了大量的PeV CR。我们约束的条件下，银河系晕中的CR的扩散系数的CR已经到达地球上，而相当大的一部分，他们已经逃离了晕。基于扩散晕模型，我们求解了CR的扩散方程，并将结果与地球上的CR谱进行了比较。如果银盘中的扩散系数小于晕中的扩散系数，则可以解释观测到的CRs到达方向的小的各向异性。我们的模型预测，硼碳比应该是能量独立的膝盖周围，在那里的CR从Sgr A* 成为主导。在爆发时加速的CR的光谱不太可能由幂律表示，类似于银河系中心周围的中央分子带（CMZ）的伽马射线发射。
Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ("Pevatron"). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 107 yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.