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arXiv 0902.0376astro-ph.HEhep-ph
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超新星遗迹分布的不均匀性是PAMELA异常的起源

Inhomogeneity in the Supernova Remnant Distribution as the Origin of the PAMELA Anomaly

Nir J. Shaviv, Ehud Nakar, Tsvi Piran

摘要:

最近对宇宙射线(CR)通量中正电子/电子比率的测量显示出明显的异常,该比率在10至100 GeV之间增加。我们发现,CR源的不均匀性的规模为一个千秒差距,自然可以解释这种异常。如果最近的主要CR源距离我们大约1千秒差距,那么低能电子($\sim 1$ GeV)可以很容易地到达我们。在更高的能量($\gtrsim 10$ GeV)下,源电子在到达地球之前通过同步加速器和逆康普顿冷却。通过质子/ISM相互作用在当地附近形成的对也可以以高能量到达地球,从而增加正电子/电子比。源不均匀性的一个自然起源是超新星在银河系旋臂中的高度集中。假设超新星遗迹(SNRs)作为唯一的主要来源的CR,并考虑到他们的浓度附近的银河系旋臂,我们一贯恢复观察到的正电子分数之间的1和100 GeV。ATIC在$\sim 600$ GeV处的电子过剩在这幅图中被解释为附近几个已知SNR的贡献。该模型预测了10 GeV电子冷却时间(正电子/电子比上升)、$\sim 10$ Myr和相同能量的CRs质子宇宙起源年龄之间的表观一致相似性。

英文摘要:

Recent measurements of the positron/electron ratio in the cosmic ray (CR) flux exhibits an apparent anomaly, whereby this ratio increases between 10 and 100 GeV. We show that inhomogeneity of CR sources on a scale of order a kpc, can naturally explain this anomaly. If the nearest major CR source is about a kpc away, then low energy electrons ($\sim 1$ GeV) can easily reach us. At higher energies ($\gtrsim 10$ GeV), the source electrons cool via synchrotron and inverse-Compton before reaching Earth. Pairs formed in the local vicinity through the proton/ISM interactions can reach Earth also at high energies, thus increasing the positron/electron ratio. A natural origin of source inhomogeneity is the strong concentration of supernovae in the galactic spiral arms. Assuming supernova remnants (SNRs) as the sole primary source of CRs, and taking into account their concentration near the galactic spiral arms, we consistently recover the observed positron fraction between 1 and 100 GeV. ATIC's electron excess at $\sim 600$ GeV is explained, in this picture, as the contribution of a few known nearby SNRs. The apparent coincident similarity between the cooling time of electrons at 10 GeV (where the positron/electron ratio upturn), $\sim 10$ Myr, and the CRs protons cosmogenic age at the same energy is predicted by this model.

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