标题： 宇宙线在银河超新星遗迹周围的面密度 显示英文标题

标题： Grammage of cosmic rays around Galactic supernova remnants

摘要： 宇宙射线（CRs）在银河系中的停留时间通常通过次级核与初级核的比值测量得出，例如硼（B）与碳（C）的比值，这提供了一个估计值，表示CRs在传播过程中穿越的物质量，即所谓的CR grammage。 然而，在被其母源释放后，例如超新星遗迹（SNRs），CRs必须穿过银河系的盘，然后进入密度低得多的晕，在其中被认为花费大部分时间，最终逃逸出银河系。 在近源区域，CR的传播被证明是由波的非线性自生成主导。 在这里我们表明，由于这种效应，能量高达$\sim$10 TeV的CRs在距离源$L_{c}\sim 100$pc范围内的停留时间远大于直观估计所暗示的。 相应的grammage接近当前对整个银河系中总grammage的估计。 此外，CRs在加速它们的激波下游被困时，会穿越一个不可消除的grammage，尽管这一贡献相当不确定。 我们得出结论，在能量$\lesssim 1$TeV时，观测到的grammage受到近源非线性捕获的显著影响，而在能量$\gtrsim 1$TeV时则受到源grammage的影响。 因此，B/C比值的测量应谨慎用作CRs在大尺度银河系传播的指示器。 显示英文摘要

摘要： The residence time of cosmic rays (CRs) in the Galaxy is usually inferred from the measurement of the ratio of secondary-to-primary nuclei, such as the boron (B)/carbon (C) ratio, which provides an estimate of the amount of matter traversed by CRs during their propagation, the so called CR grammage. However, after being released by their parent sources, for instance supernova remnants (SNRs), CRs must cross the disc of the Galaxy, before entering the much lower density halo, in which they are believed to spend most of the time before eventually escaping the Galaxy. In the near-source region, the CR propagation is shown to be dominated by the non-linear self-generation of waves. Here we show that due to this effect, the time that CRs with energies up to $\sim$ 10 TeV spend within a distance $L_{c}\sim 100$ pc from the sources is much larger than naive estimates would suggest. The corresponding grammage is close to current estimates of the total grammage traversed throughout the whole Galaxy. Moreover, there is an irreducible grammage that CRs traverse while trapped downstream of the shock that accelerated them, though this contribution is rather uncertain. We conclude that at energies $\lesssim 1$ TeV, the observed grammage is heavily affected by the near-source non-linear trapping of CRs, and at energies $\gtrsim 1$ TeV it is affected by the source grammage. As a result, the measurement of the B/C ratio should be used very cautiously as an indicator of the propagation of CRs on large Galactic scales.