H. Akamatsu, R. J. van Weeren, G. A. Ogrean, H. Kawahara, A. Stroe, D. Sobral, M. Hoeft, H. J. A. Röttgering, M. Brüggen, J. S. Kaastra

Abstract
Context. We present the results from Suzaku observations of the merging cluster of galaxies CIZA J2242.8+5301 at z = 0.192.
Aims. To study the physics of gas heating and particle acceleration in cluster mergers, we investigated the X-ray emission from CIZA J2242.8+5301, which hosts two giant radio relics in the northern and southern part of the cluster.
Methods. We analyzed data from three-pointed Suzaku observations of CIZA J2242.8+5301 to derive the temperature distribution in four different directions.
Results. The intracluster medium (ICM) temperature shows a remarkable drop from 8.5_-0.6^+0.8 keV to 2.7_-0.4^+0.7 keV across the northern radio relic. The temperature drop is consistent with a Mach number ℳ_n = 2.7^+0.7_-0.4 and a shock velocity v_shock:n = 2300_-400⁺⁷⁰⁰ km s^-1. We also confirm the temperature drop across the southern radio relic. However, the ICM temperature beyond this relic is much higher than beyond the northern relic, which gives a Mach number ℳ_s = 1.7^+0.4_-0.3 and shock velocity v_shock:s = 2040_-410⁺⁵⁵⁰ km s^-1. These results agree with other systems showing a relationship between the radio relics and shock fronts which are induced by merging activity. We compare the X-ray derived Mach numbers with the radio derived Mach numbers from the radio spectral index under the assumption of diffusive shock acceleration in the linear test particle regime. For the northern radio relic, the Mach numbers derived from X-ray and radio observations agree with each other. Based on the shock velocities, we estimate that CIZA J2242.8+5301 is observed approximately 0.6 Gyr after core passage. The magnetic field pressure at the northern relic is estimated to be 9% of the thermal pressure.

Keywords
shock waves - methods: data analysis - galaxies: clusters: individual: CIZA J2242.8+5301 - X-rays: galaxies: clusters - galaxies: clusters: intracluster medium

Astronomy & Astrophysics
Volume 582, Number of pages A87
2015 October

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