X-Ray View of the Shock Front in the Merging Cluster Abell 3376 with Suzaku

Abstract

We report on a Suzaku measurement of the shock feature associated with the western radio relic in the merging cluster A 3376. The temperature profile is characterized by an almost flat radial shape with kT ∼ 4 keV within 0.5r₂₀₀ and a rise by about 1 keV inside the radio relic. Across the relic region (0.6-0.8r₂₀₀), the temperature shows a remarkable drop from about 4.7 keV to 1.3 keV. This is clear evidence that the radio relic really corresponds to a shock front, possibly caused by a past major merger. The observed sharp changes of the temperature and electron density indicate the Mach number M ∼ 3. The radial entropy profile is flatter than the prediction (r^1.1) of numerical simulations within 0.5r₂₀₀, and becomes steeper around the relic region. These observed features and time-scale estimation consistently imply that the ICM around the radio relic has experienced a merger shock, and is in the middle of the process of dynamical and thermal relaxations.