Suzaku X-ray study of the double radio relic galaxy cluster CIZA J2242.8+5301

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: H.Akamatsu@sron.nl
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Department of Earth and Planetary Science, The University of Tokyo, 113-0033 Tokyo, Japan
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Hamburg Observatory, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁶ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018 Lisboa, Portugal
⁸ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016 Lisbon, Portugal

Received: 23 October 2014
Accepted: 8 July 2015

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.