We present the results of deep Chandra and XMM-Newton X-ray imaging and spatially-resolved spectroscopy of Abell 2256, a nearby (z=0.058) galaxy cluster experiencing multiple mergers and displaying a rich radio morphology dominated by a large relic. The X-ray data reveals three subclusters: (i) the `main cluster'; (ii) the remnant of an older merger in the east of the cluster with a ~ 600 kpc long tail; (iii) a bright, bullet-like, low-entropy infalling system, with a large line-of-sight velocity component. The low-entropy system displays a 250 kpc long cold front with a break and an intriguing surface brightness decrement. Interestingly, the infalling gas is not co-spatial with bright galaxies and the radio loud brightest cluster galaxy of the infalling group appears dissociated from the low entropy plasma by 50 kpc in projection, to the south of the eastern edge of the cold front. Assuming that the dark matter follows the galaxy distribution, we predict that it is also significantly offset from the low-entropy gas. Part of the low frequency radio emission near the cold front might be revived by magnetic field amplification due to differential gas motions. Using analytical models and numerical simulations, we investigate the possibility that the supersonic infall of the subcluster generates a large scale shock along our line-of-sight, which can be detected in the X-ray temperature map but is not associated with any clear features in the surface brightness distribution.
A Deep X-Ray Look At Abell 2142 --- Viscosity Constraints From Kelvin-Helmholtz Eddies, A Displaced Cool Peak That Makes A Warm Core, And A Possible Plasma Depletion Layer
我们分析了钱德拉ACIS观测的合并星系团A2142的200 KS详细检查其突出的冷锋。我们发现，南方冷锋在天空平面上表现出非常发达的开尔文-亥姆霍兹（KH）涡旋。通过与粘性气体冷锋的流体动力学模拟结果比较，并根据气体的向心加速度估算气体的切向速度，我们将有效粘性约束为Spitzer各向同性粘性的1/5，但与磁化等离子体的Braginskii各向异性粘性一致.虽然西北锋没有显示出明显的涡旋，但它的形状和亮度廓线的结构表明在投影中看到了KH涡旋。南部冷锋继续以螺旋形向星团中心移动，最后以另一个冷锋结束，距离气体密度峰值仅12千秒差距。冷峰本身距离BCG约30 kpc（在中心峰值集群中最大的这种偏移），而更大尺度上的X射线发射仍然以BCG为中心，表明BCG处于重力势的中心，冷气体在其中晃动。（$K\approx49$ keV cm $^2$）使A2142成为一个罕见的“暖核”;显然，晃动引起的冷峰位移很大是原因。最后，我们发现一个微妙的狭窄，直的通道，X射线亮度下降10%，与南部冷锋对齐-可能是投影中的等离子体耗尽层。
A Gamma-ray Emitting Head-Tail Radio Galaxy Swimming Through the Hot Medium of the Merging Cluster Abell 3627
Inter-University Centre for Astronomy and Astrophysics (IUCAA)（天文与天体物理大学间中心）；Centre for Space Research, North-West University（西北大学太空研究中心）；International Gemini Observatory/NSF NOIRLab（国际双星观测台/美国国家光学红外天文实验室）；Indian Institute of Astrophysics（印度天体物理研究所）；Universität Bielefeld（比勒费尔德大学）；Assam Don Bosco University（阿萨姆唐博斯科大学）；Dayanand Science College（戴亚南德科学学院）
Discovery of Gas Bulk Motion in the Galaxy Cluster Abell 2256 with Suzaku
本文介绍了朱雀星对星系团Abell 2256的观测结果。这个星系团是一个典型的和充分研究的合并系统，表现出在X射线表面亮度和径向速度分布的成员星系的子结构。在天空中存在主分量和次分量，主分量和次分量的间距为3 '.5，在成员星系径向速度峰中存在主分量和次分量，主分量和次分量的间距为$^{-1}$约2000 km s。为了用朱雀XIS测量来自两种气体组分的铁K壳层线的多普勒频移，仔细评估了仪器的能量标度，发现校准良好。一个显着的移动的子组分气体的径向速度相对于主集群被检测到。所有三个XIS传感器都独立地显示三个传感器之间的一致性。发现差异为1500 $\pm 300$（统计）$\pm 300$（系统）km s $^{-1}$。X射线测定的绝对红移值以及主分量和次分量之间的差值与成员星系的绝对红移值在光学上一致。观测结果有力地表明，发射X射线的气体作为星系团内的子结构与星系一起移动。这些结果与其他X射线观测气体整体运动合并集群进行了讨论。
