Although radio relics are understood to originate in intracluster shock waves resulting from merger shocks, the most widely used model for describing this (re-)acceleration process at shock fronts, the diffusive shock acceleration (DSA) model, has several challenges, including the fact that it is inefficient at low shock Mach numbers. In light of these challenges, it is worthwhile to consider alternative mechanisms. One possibility is the adiabatic compression by a shock wave of a residual fossil electron population which has been left over from a radio galaxy jet. This paper applies this model to the relic hosted in the merging galaxy cluster Abell 3411-3412, where a radio bridge between the relic and a radio galaxy has been observed, with the aim to reproduce the spatial structure of the spectral index of the relic. Four scenarios are presented, in which different effects are investigated, such as effects behind the shock front and different shock strengths. The results show that the adiabatic compression model can reproduce the observed spectral indices across the relic for a shock Mach number that is lower than the value required by the DSA-type modelling of this relic and is in accordance with the values derived from X-ray observations, if other mechanisms, such as an expansion phase or post-shock turbulence, are effective behind the shock front.

中文翻译：

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绝热压缩方案在Abell 3411-3412星系团射电遗迹中的应用

尽管无线电遗迹被认为起源于合并激波产生的簇内激波，但描述激波前沿（重新）加速过程的最广泛使用的模型，即扩散激波加速 (DSA) 模型存在若干挑战，包括以下事实：它在低冲击马赫数下效率低下。鉴于这些挑战，值得考虑替代机制。一种可能性是由射电星系喷流遗留下来的残余化石电子群的冲击波造成的绝热压缩。本文将该模型应用于合并星系团 Abell 3411-3412 中的遗迹，在那里观测到遗迹与射电星系之间的射电桥，旨在再现遗迹光谱指数的空间结构。介绍了四种场景，其中研究了不同的影响，例如冲击波前的影响和不同的冲击强度。结果表明，绝热压缩模型可以重现观测到的整个遗迹的光谱指数，该指数低于该遗迹的 DSA 型建模所需的值，并且与从 X 射线得出的值一致。观察，如果其他机制，如膨胀阶段或冲击后湍流，在冲击波前是否有效。