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

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 +0.8 −0.6 keV to 2.7 +0.7 −0.4 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 +700 −400 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 +550 −410 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.

Turbulent cosmic ray reacceleration and the curved radio spectrum of the radio relic in the Sausage Cluster

“…The hard X-ray flux from inverse Compton scattering is larger than the synchrotron flux, because the magnetic field of B d = 0.30 µG is smaller than BCMB ≈ 3.24(1 + z) 2 µG ≈ 4.6 µG, at which synchrotron cooling is comparable to the cooling by inverse Compton scattering. 1 We analyze the Suzaku data of the Sausage Cluster (see Akamatsu et al 2015) and find that the upper limit of the nonthermal emission is 8.2×10 −13 erg s −1 in the 0.3-10 keV band, which is consistent with our prediction in figure 3b.…”

Radio relics tracing the projected mass distribution in CIZA J2242.8+5301

“…′ 4, respectively. Interestingly, the distance ratio is approximately equal to the ratio of the Mach numbers estimated by X-ray temperature, (Akamatsu et al 2015), where M NR = 2.7 Since the distance is equivalent to the merger timescale multiplied by the velocity, those positions relative to the center of mass are simply explained by the timescale after the core passage. In other words, the formation of radio relic is possibly triggered after the core passage.…”

“…Brunetti & Jones 2014) and the spectral aging (van Weeren et al 2010) suggest that radio relics are connected with merger shocks. Indeed, X-ray observations (Akamatsu & Kawahara 2013;Akamatsu et al 2015) discovered the temperature jump around the radio relics, though the Mach numbers estimated by X-ray observation (M NR = 2.7 ± 0.5 and M SR = 1.7 ± 0.3). are somewhat lower than those (M NR = 4.58 ± 1.09 and M SR = 2.81 ± 0.19) by radio spectral index based on DSA model [Vol.…”

“…Overlaid contours (white) are the radio emission (Stroe et al 2013) at 1.2 GHz in units of signal-to-noise ratio [4,8,16, 32]σ RMS . Middle: X-ray image of Suzaku satellite in 0.5 − 2.0keV (Akamatsu & Kawahara 2013;Akamatsu et al 2015). Right : Luminosity map for bright member galaxies (Sec 3) computed with Gaussian smoothing FWHM= 3.…”

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

“…Vazza & Brüggen (2014) andVazza et al (2015 show that the observed γ-rayupper limits are in tension with the relative acceleration efficiency of electrons and protons that is expected from DSA. Tension with DSA has also been found from the discrepancy between the measured Mach numbers from X-ray observations and the radio spectral index (see Equation (3)) for some relics (e.g., Akamatsu et al 2015;Itahana et al 2015;van Weeren et al 2016a).…”