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arXiv 0905.0904astro-ph.HE
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超新星遗迹中的不均匀性作为PAMELA/ATIC观测的自然解释

Inhomogeneity in the Supernova Remnants as a Natural Explanation of the PAMELA/ATIC Observations

Tsvi Piran, Nir J. Shaviv, Ehud Nakar

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。与此相反,根据标准方案,CR正电子是由初级CR质子和星际介质(ISM)之间的强子相互作用二次形成的,这个比率应该会降低。因此,正电子过剩被解释为弱相互作用的大质量粒子湮灭/衰变的证据,或者是对的直接天体物理来源。所有提出的模型的共同特点是,他们调用新的物理或新的天体物理来源。然而,这条论证线隐含地依赖于相对均匀的CR源分布的假设。CR源在千秒差距量级上的不均匀性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(~GeV)可以很容易地到达我们。在更高的能量(> 10 GeV)下,源电子在到达太阳附近之前通过同步加速器和逆康普顿冷却。通过质子/ISM相互作用在局部附近形成的对也可以以高能量到达太阳系,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星系旋臂的强烈聚集。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,我们一贯预测观测到的正电子分数之间的1和100 GeV,同时遵守不同的限制,如观测到的电子光谱和CR宇宙起源年龄。在这张照片中,在~600 GeV处的ATIC光谱过剩可以解释为附近几个已知的SNR的贡献。

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. In contrast, this ratio should decrease according to the standard scenario, in which CR positrons are secondaries formed by hadronic interactions between the primary CR protons and the interstellar medium (ISM). The positron excess is therefore interpreted as evidence for either an annihilation/decay of weakly interacting massive particles, or for a direct astrophysical source of pairs. The common feature of all proposed models is that they invoke new physics or new astrophysical sources. However, this line of argumentation relies implicitly on the assumption of a relatively homogeneous CR source distribution. 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 (~GeV) can easily reach us. At higher energies (> 10 GeV), the source electrons cool via synchrotron and inverse-Compton before reaching the solar vicinity. Pairs formed in the local vicinity through the proton/ISM interactions can reach the solar system also at high energies, thus increasing the positron/electron ratio. A natural origin of source inhomogeneity is the strong concentration of supernovae to 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 predict the observed positron fraction between 1 and 100 GeV, while abiding to different constraints such as the observed electron spectrum and the CRs cosmogenic age. An ATIC like spectral excess at ~600 GeV can be explained, in this picture, as the contribution of a few known nearby SNRs.

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