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

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 similar to 4 keV within 0.5 r(200) and a rise by about 1 keV inside the radio relic. Across the relic region (0.6-0.8 r200), 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 similar to 3. The radial entropy profile is flatter than the prediction (r(1.1)) of numerical simulations within 0.5 r(200), 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.