在ZwCl1447 .2+2619中发现双射电遗迹：具有特殊表面亮度比的冲击加速度模型的罕见试验台
Discovery of a double radio relic in ZwCl1447.2+2619: A rare testbed for shock acceleration models with a peculiar surface brightness ratio
摘要：
我们报告了在星团合并ZwCl 1447.2 +2619（$z=0.376$）中发现的一个双射电遗迹，并在$420\rm~MHz$和$700\rm~MHz$进行了uGMRT观测。北、南遗迹的线性尺寸分别为$\sim0.3~$ Mpc和$\sim1.2~$ Mpc，这与理论预期的在质量较小的子星系团一侧产生较大遗迹相一致。然而，ZwCl 1447.2 +2619与其他已知的双射电遗迹系统不同，在其他已知的双射电遗迹系统中，较大的遗迹由于几个因素而更加明亮。在这次合并中，较小的北部遗迹的较高表面亮度使其总射电光度与较大的南部遗迹相当。这两个射电遗迹的表面亮度比$\sim0.1$与其它双射电遗迹系统中观测到的表面亮度比有很大不同。从我们的射电频谱分析，我们发现，这两个遗迹表示类似的弱激波的马赫数$2.9\pm0.8$和$2.0\pm0.7$的北部和南部的遗迹，分别。此外，北部遗迹连接到一个离散的无线电源与光学对应物，这表明可能存在宇宙射线注入和再加速。因此，我们建议，这种非典型的表面亮度比可以解释与粒子加速效率急剧下降的弱冲击制度和/或化石宇宙射线的再加速。我们的多波长分析和数值模拟表明，ZwCl 1447.2 +2619是一个后合并，它经历了近正面碰撞$\sim0.7\rm~Gyr$前。
英文摘要：
We report a discovery of a double radio relic in the cluster merger ZwCl1447.2+2619 ($z=0.376$) with uGMRT observations at $420\rm~MHz$ and $700\rm~MHz$. The linear sizes of the northern and southern relics are $\sim0.3~$Mpc and $\sim1.2~$Mpc, respectively, which is consistent with the theoretical expectation that a larger relic is produced in the less massive subcluster side. However, ZwCl1447.2+2619 is unlike other known double radio relic systems, where the larger relics are much more luminous by several factors. In this merger the higher surface brightness of the smaller northern relic makes its total radio luminosity comparable to that of the much larger southern relic. The surface brightness ratio $\sim0.1$ between the two radio relics differs significantly from the relation observed in other double radio relic systems. From our radio spectral analysis, we find that both relics signify similar weak shocks with Mach numbers of $2.9\pm0.8$ and $2.0\pm0.7$ for the northern and southern relics, respectively. Moreover, the northern relic is connected to a discrete radio source with an optical counterpart, which indicates the possible presence of cosmic ray injection and re-acceleration. Therefore, we propose that this atypical surface brightness ratio can be explained with the particle acceleration efficiency precipitously dropping in the weak shock regime and/or with re-acceleration of fossil cosmic rays. Our multi-wavelength analysis and numerical simulation suggest that ZwCl1447.2+2619 is a post-merger, which has experienced a near head-on collision $\sim0.7\rm~Gyr$ ago.
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