Title: How unusual is the cool-core radio halo cluster CL1821+643 ? Show Chinese title

Title: CL1821+643 降温核心射电晕团簇有多不寻常？

Abstract: Massive galaxy clusters with cool-cores typically host diffuse radio sources called mini-haloes, whereas, those with non-cool-cores host radio haloes. We attempt to understand the unusual nature of the cool-core galaxy cluster CL1821+643 that hosts a Mpc-scale radio halo using new radio observations and morphological analysis of its intra-cluster medium. We present the Giant Metrewave Radio Telescope (GMRT) 610 MHz image of the radio halo. The spectral index, $\alpha$ defined as $S\propto \nu^{-\alpha}$, of the radio halo is $1.0\pm0.1$ over the frequency range of 323 - 610 - 1665 MHz. Archival {\it Chandra} X-ray data were used to make surface brightness and temperature maps. The morphological parameters Gini, $M_{20}$ and concentration ($C$) were calculated on X-ray surface brightness maps by including and excluding the central quasar (H1821+643) in the cluster. We find that the cluster CL1821+643, excluding the quasar, is a non-relaxed cluster as seen in the morphological parameter planes. It occupies the same region as other merging radio halo clusters in the temperature- morphology parameter plane. We conclude that this cluster has experienced a non-core-disruptive merger. Show Chinese abstract

Abstract: 大质量具有冷核心的星系团通常包含称为小晕的弥散射电源，而那些没有冷核心的星系团则包含射电晕。我们尝试通过新的射电观测和对星系团内介质的形态分析来理解具有Mpc尺度射电晕的冷核心星系团CL1821+643的异常性质。我们展示了巨米波射电望远镜（GMRT）610 MHz的射电晕图像。射电晕的光谱指数，$\alpha$定义为$S\propto \nu^{-\alpha}$，在323 - 610 - 1665 MHz的频率范围内为$1.0\pm0.1$。利用档案中的{\it 钱德拉}X射线数据制作了表面亮度和温度图。通过在集群中包括和排除中心类星体（H1821+643），计算了X射线表面亮度图上的形态参数Gini，$M_{20}$和集中度（$C$）。我们发现，排除类星体后，该星系团CL1821+643在形态参数平面上是一个非平衡的星系团。它在温度-形态参数平面上与其他合并射电晕星系团占据相同区域。我们得出结论，这个星系团经历了一次非核心破坏性的合并。