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arXiv 2312.06992astro-ph.HE
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在宇宙线“膝”与“踝”之间:来自星团的贡献

Between the cosmic-ray `knee' and the `ankle': Contribution from star clusters

Sourav Bhadra, Satyendra Thoudam, Biman B Nath, Prateek Sharma

AI总结:

本文提出大质量年轻星团可加速膝与踝之间(10^7–10^9 GeV)的银河宇宙线,通过星风产生核素并考虑传播与再加速,模型要求源谱截断为5×10^7 Z GeV且注入份额约为星风动能5%,支持星团作为银河宇宙线第二成分的天然加速器。

摘要:

我们表明,大质量年轻星团可能是能够在 $10^7\hbox{--}10^9$ GeV(即“膝”与“踝”之间)范围内加速银河宇宙线的候选天体。由于在超新星遗迹加速宇宙线的标准范式中难以将粒子加速到 $10^7\hbox{--}10^9$ GeV 范围,人们已提出多种可能的方案,例如在星风终止激波处加速、在这些年轻星团内部的超新星激波中加速等。我们利用观测到的银河系盘面年轻星团分布,考虑了一个从大质量星风产生不同宇宙线核的模型。我们给出了宇宙线在银河系中传播的详细计算,其中考虑了扩散、传播过程中的相互作用损失以及年老超新星遗迹对粒子的再加速效应,以确定全粒子宇宙线能谱。利用 Hillas 判据对最大能量的估计,我们认为一个年轻的大质量星团可以将质子加速到几十 PeV。与观测数据比较后,我们的模型要求这些星团提供的宇宙线源谱具有 $5\times 10^7 Z$ GeV($50\\,Z$~PeV)的指数截断,同时宇宙线注入份额约为星风动能的 $\sim 5\\%$。在将星团视为银河宇宙线“第二成分”的天然加速器的背景下,我们讨论了在星团中实现这些要求的可能性以及相关的不确定性。

英文摘要:

We show that massive young star clusters may be possible candidates that can accelerate Galactic cosmic rays (CRs) in the range of $10^7\hbox{--}10^9$ GeV (between the `knee' and `ankle'). Various plausible scenarios such as acceleration at the wind termination shock (WTS), supernova shocks inside these young star clusters, etc. have been proposed,since it is difficult to accelerate particles up to the $10^7\hbox{--}10^9$ GeV range in the standard paradigm of CR acceleration in supernova remnants. We consider a model for the production of different nuclei in CRs from massive stellar winds using the observed distribution of young star clusters in the Galactic plane. We present a detailed calculation of CR transport in the Galaxy, taking into account the effect of diffusion, interaction losses during propagation, and particle re-acceleration by old supernova remnants to determine the all-particle CR spectrum. Using the maximum energy estimate from the Hillas criterion, we argue that a young massive star cluster can accelerate protons up to a few tens of PeV. Upon comparison with the observed data, our model requires a CR source spectrum with an exponential cutoff of $5\times 10^7 Z$ GeV ($50\,Z$~PeV) from these clusters together with a cosmic-ray injection fraction of $\sim 5\%$ of the wind kinetic energy. We discuss the possibility of achieving these requirements in star clusters, and the associated uncertainties, in the context of considering star clusters as the natural accelerator of the `second component' of Galactic cosmic rays.

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