Supernova remnants (SNRs) have been regarded as major acceleration sites of Galactic cosmic rays. Recent X-ray studies revealed neutral Fe K$\alpha$ line emission from dense gas in the vicinity of some SNRs, which can be best interpreted as K-shell ionization of Fe atoms in the gas by sub-relativistic particles accelerated in the SNRs. In this Letter, we propose a novel method of constraining the composition of particles accelerated in SNRs, which is currently unknown. When energetic heavy ions collide with target atoms, their strong Coulomb field can easily cause simultaneous ejection of multiple inner-shell electrons of the target. This results in shifts in characteristic X-ray line energies, forming distinctive spectral structures. Detection of such structures in the neutral Fe K$\alpha$ line strongly supports the particle ionization scenario, and furthermore provides direct evidence of heavy ions in the accelerated particles. We construct a model for the Fe K$\alpha$ line structures by various projectile ions utilizing atomic-collision data.

中文翻译：

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用多次电离过程产生的Fe Kα线结构探测宇宙射线

超新星遗迹 (SNR) 被认为是银河系宇宙射线的主要加速点。最近的 X 射线研究揭示了一些 SNR 附近致密气体的中性 Fe K$\alpha$ 线发射，这可以最好地解释为 SNR 中加速的亚相对论粒子对气体中 Fe 原子的 K 层电离. 在这封信中，我们提出了一种限制 SNR 中加速粒子组成的新方法，这是目前未知的。当高能重离子与靶原子碰撞时，其强大的库仑场很容易引起靶的多个内壳电子同时喷射。这导致特征 X 射线线能量发生变化，形成独特的光谱结构。在中性 Fe K$\alpha$ 线中检测到这种结构强烈支持粒子电离场景，并且进一步提供了加速粒子中重离子的直接证据。我们利用原子碰撞数据构建了各种射弹离子的 Fe K$\alpha$ 线结构模型。