Suzaku and XMM-Newton observations of the newly discovered early-stage cluster merger of 1E2216.0-0401 and 1E2215.7-0404

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: h.akamatsu@sron.nl
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 8 July 2016
Accepted: 3 August 2016

Abstract

We present the results of Suzaku and XMM-Newton X-ray observations of the cluster pair 1E2216.0-0401 and 1E2215.7-0404. We discover an X-ray bridge between the clusters. Suzaku and XMM-Newton observations revealed that each cluster hosts gas with moderate temperature of kT₀₄₀₁ = 4.8 ± 0.1 keV and kT₀₄₀₄ = 5.8 ± 0.2 keV, respectively. On the other hand, the bridge region shows a remarkably high temperature (kT = 6.6 ± 0.5 keV). Furthermore, at the position of the bridge, we detected an enhancement in the wavelet-decomposed soft-band (0.5−4.0 keV) XMM-Newton image at 3 sigma significance, this is most likely due to a compression of the intracluster medium (ICM) as a consequence of the merging activity. This X-ray intensity and temperature enhancement are not consistent with those expected from a late phase, but are in agreement with the predictions by numerical simulations of an early phase merger. From the temperature jump at the location of the bridge, the Mach number is estimated to be ℳ = 1.4 ± 0.1, which corresponds to a shock propagation velocity of about 1570 km s^-1. From the shock properties, we estimate that core-passage will occur in 0.3−0.6 Gyr and that the age of the shock structure is 50−100 Myr. Based on the measured properties of the ICM at the bridge and estimation of timescales, we find indications for non-equilibrium ionization. We also discover possible diffuse radio emission located between the merging clusters. Combining the radio, X-ray, and optical image data, we speculate that the detected radio sources are most likely related to the merger event. Thus, 1E2216.0-0401 and 1E2215.7-0404 is a new example of an early phase cluster merger with remarkable characteristics.