Hiroki Akamatsu (SRON)

Title: Exploring Energetics at the Largest Shock Structures in the Universe with Suzaku

Based on the framework of the hierarchical structure formation theory, clusters of galaxies grow though merging event with smaller objects and accretion flows from large scale structure filaments. The thermalisation history of the ICM contains instructional information of the comic baryons. In particular, merging event between massive clusters of galaxies is one of an energetic event in the Universe since the Big Bang, which release an enormous energy. These gravitational energy convert into a heating of Intra- Cluster Matter (ICM) and particle acceleration by shocks and via the mechanism of diffusive shock acceleration.

We performed systematic X-ray studies of 9 radio relic region in 7 merging clusters (e.g., Akamatsu & Kawahara 2013, etc.,). In the 7 radio relics, we confirmed significant temperature drop across the relic. It strongly indicates that presence of a shock front at radio relic. The Mach number from the measured temperature drop spans M=1.5-3.

Although our results support a scenario that these radio relics are formed via diffusive shock acceleration (DSA) by merger shocks, inferred from X-ray and radio observation are sometimes inconsistent with each other. Furthermore, our results bring up another question that observed weak shocks with M < 3 can not accelerate particles from thermal pools to relativistic energies via the DSA mechanism. In this talk, we will report our understanding and activities for these issues.

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Last-modified: 2016-09-29 (木) 07:45:45 (1662d)