化石团泡中的Cosmic ray约束
Cosmic ray confinement in fossil cluster bubbles
摘要：
大多数冷核心星系团的中心都有活动星系核（AGN）。这些活动星系核使含有非热辐射粒子的浮泡膨胀。如果这样的气泡有效地限制了宇宙射线（CR），那么这就可以解释在远离星团中心的地方看到的“无线电幽灵”。我们模拟了活动星系核膨胀的浮力气泡中宇宙射线的扩散。我们的模拟包括由磁场引入的各向异性粒子扩散的影响。我们的模型是一致的活动星系核气泡的X射线形态，与中断被抑制的磁覆盖效应。我们的结论是，对于这样的磁场拓扑结构，相当一部分的宇宙射线可以被限制在气泡内的浮力上升的时间尺度，即使当平行扩散系数是非常大的。对于在可比水平上的各向同性扩散，宇宙射线会从气泡中泄漏出来，速度太快，与射电观测结果不一致。因此，与CR扩散的磁抑制相关的长约束时间可以解释无线电鬼的存在。我们发现，宇宙射线的部分逃逸主要局限于上升气泡的尾流，并推测这种效应可能：（1）解释了英仙座星系团中气泡后面的H $α$细丝的激发，（2）将熵注入到被气泡提升的富含金属的物质中，因此，有助于使它永久地离开星团中心;（3）通过漫射宇宙射线与热星团内介质（ICM）的相互作用产生可观测的$γ$射线。
英文摘要：
Most cool core clusters of galaxies possess active galactic nuclei (AGN) in their centers. These AGN inflate buoyant bubbles containing non-thermal radio emitting particles. If such bubbles efficiently confine cosmic rays (CR) then this could explain ``radio ghosts'' seen far from cluster centers. We simulate the diffusion of cosmic rays from buoyant bubbles inflated by AGN. Our simulations include the effects of the anisotropic particle diffusion introduced by magnetic fields. Our models are consistent with the X-ray morphology of AGN bubbles, with disruption being suppressed by the magnetic draping effect. We conclude that for such magnetic field topologies, a substantial fraction of cosmic rays can be confined inside the bubbles on buoyant rise timescales even when the parallel diffusivity coefficient is very large. For isotropic diffusion at a comparable level, cosmic rays would leak out of the bubbles too rapidly to be consistent with radio observations. Thus, the long confinement times associated with the magnetic suppression of CR diffusion can explain the presence of radio ghosts. We show that the partial escape of cosmic rays is mostly confined to the wake of the rising bubbles, and speculate that this effect could: (1) account for the excitation of the H$α$ filaments trailing behind the bubbles in the Perseus cluster, (2) inject entropy into the metal enriched material being lifted by the bubbles and, thus, help to displace it permanently from the cluster center and (3) produce observable $γ$-rays via the interaction of the diffusing cosmic rays with the thermal intracluster medium (ICM).
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