A rare, strong shock front in the merging galaxy cluster SPT-CLJ2031-4037

Galaxy Clusters are the largest gravitationally bound structures in the Universe. Mergers of galaxy clusters are the most energetic events in the Universe after the Big Bang. In such mergers, the sub-clusters collide at velocities of 10³ km s^-1, thus releasing energy of the order of 10⁶⁴ erg. This energy is dissipated into the Intracluster Medium (or ICM; the hot ionized plasma that permeates through a galaxy cluster), via shocks. Strong shocks traveling through the ICM can reveal the formation history of the cluster. Only a handful of such strong shocks, with Mach number M > 2 have been observed so far. We present our findings from the new deep Chandra observations (~256 ks) of the merging galaxy cluster SPT-CLJ2031-4037 at z=0.34. Our observations reveal intricate structures seen in a major merger akin to the Bullet Cluster. The X-ray data confirm the existence of two shock fronts (i. the primary shock front , and ii. the southeastern edge) by directly measuring the temperature jump of gas across the surface brightness edges. The primary shock front has a Mach number of M =2.28^+1.01_-0.58 , 𝑀 = 2.24^+0.46_−0.36, and M = 2.15^+0.42_−0.32 on sectors along the sharp edge, which makes it one of the rare merging systems with a Mach number 𝑀 > 2. The southeastern edge has a lower Mach number M = 1.04 ±0.15. Strong merger shocks provide for an excellent experimental setup to determine the method of electron-ion equilibration in the ICM. The electron temperature profiles of the Bullet cluster (M = 3.0 ± 0.4) indicate that the instant shock heating model is the preferred method of shock heating, while for A2146 (M = 2.3 ± 0.3) it is the adiabatic-collisional method of equilibration. For SPT-CLJ2031-4037, we determined from the electron temperature profile in the post-shock region of the primary shock front that the preferred method of shock heating is the adiabatic-collisional model and the temperature profile across the Southeastern edge shock front are more consistent with the Instant shock-heating model.