2017ApJ...834..159E

We present results of deep 153 ks Chandra observations of the hot, 11 keV, galaxy cluster associated with the radio galaxy 3C 438. By mapping the morphology of the hot gas and analyzing its surface brightness and temperature distributions, we demonstrate the presence of a merger bow shock. We identify the presence of two jumps in surface brightness and in density located at ∼400 and ∼800 kpc from the cluster's core. At the position of the inner jump, we detect a density jump by a factor of 2.3 ± 0.2, while at the location of the outer jump, we detect a density drop by a factor of 3.5 ± 0.7. Combining this with the temperature distribution within the cluster, we establish that the pressure of the hot gas is continuous at the 400 kpc jump, while there is a pressure change by a factor of 6.2 ± 2.8 at the 800 kpc jump. From the magnitude of the outer pressure discontinuity, using the Rankine-Hugoniot jump conditions, we determine that the sub-cluster is moving at M = 2.3 ± 0.5, or approximately 2600 ± 565 km s^–1, through the surrounding intracluster medium, creating the conditions for a bow shock. Based on these findings, we conclude that the pressure discontinuity is likely the result of an ongoing major merger between two massive clusters. Since few observations of bow shocks in clusters have been made, this detection can contribute to the study of the dynamics of cluster mergers, which offers insight into how the most massive clusters may have formed.