银河系PeVatrons和帮助发现它们：银河系吸收对观测到的非常高能量$γ$射线源光谱的影响
Galactic PeVatrons and helping to find them: Effects of Galactic absorption on the observed spectra of very high energy $γ$-ray sources
摘要：
宇宙射线（CR）“PeVatrons”是能够将粒子加速到$\sim10^{15}$ eV能量或更高能量的源，对它的识别可能导致解决全粒子CR光谱中被称为“膝”的光谱特征的起源这一长期存在的问题。由于具有这些能量的CR被星际磁场偏转，因此更有可能通过非常高能量的$γ$射线发射来识别单个源并确定其光谱特性，这提供了必要的方向信息。然而，对星际辐射场（ISRF）和宇宙微波背景的产生导致陡峭的高能尾部的$γ$射线光谱，并应进行校正，使真正的属性的频谱源被恢复。采用最近开发的三维ISRF模型，本文量化的对吸收的影响，在银河系中心方向的源在8.5 kpc和23.5 kpc的距离，与后者对应的远侧的银河系恒星盘，预计歧视的光谱特征$>10$ TeV将可能由即将到来的切伦科夫望远镜阵列。估计表明，在TeV $γ$射线望远镜迄今为止采样的能量范围内，光谱截止值可能被低估了几个因素。作为一个例子来说明这一点，最近的HESS测量扩散$γ$射线发射可能与注入CR附近的Sgr A $^*$ ISRF校正，并重新评估光谱截止的估计。它被发现，它可以更高的一个因素$\sim 2$，表明这些排放可能是一致的CR加速器与光谱截止至少1 PeV在95%的置信水平。
英文摘要：
Identification of the cosmic-ray (CR) `PeVatrons', which are sources capable of accelerating particles to $\sim10^{15}$ eV energies and higher, may lead to resolving the long-standing question of the origin of the spectral feature in the all-particle CR spectrum known as the `knee'. Because CRs with these energies are deflected by interstellar magnetic fields identification of individual sources and determination of their spectral characteristics is more likely via very high energy $γ$-ray emissions, which provide the necessary directional information. However, pair production on the interstellar radiation field (ISRF) and cosmic microwave background leads to steepening of the high-energy tails of $γ$-ray spectra, and should be corrected for to enable true properties of the spectrum at source to be recovered. Employing recently developed three-dimensional ISRF models this paper quantifies the pair-absorption effect on spectra for sources in the Galactic centre direction at 8.5 kpc and 23.5 kpc distance, with the latter corresponding to the far side of the Galactic stellar disc where it is expected that discrimination of spectral features $>10$ TeV will be possible by the forthcoming Cherenkov Telescope Array. The estimates made suggest spectral cutoffs could be underestimated by factors of a few in the energy range so far sampled by TeV $γ$-ray telescopes. As an example to illustrate this, the recent HESS measurements of diffuse $γ$-ray emissions possibly associated with injection of CRs nearby Sgr A$^*$ are ISRF-corrected, and estimates of the spectral cutoff are re-evaluated. It is found that it could be higher by up to a factor $\sim 2$, indicating that these emissions may be consistent with a CR accelerator with a spectral cutoff of at least 1 PeV at the 95% confidence level.
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