Suzaku Observation of the Ophiuchus Galaxy Cluster: One of the Hottest Cool Core Clusters

Abstract

Abstract We present the analysis of a Suzaku observation of the Ophiuchus galaxy cluster. We confirmed that the cluster has a cool core. While the temperature of the intracluster medium (ICM) decreases toward the center, the metal abundance increases. Except for the core ($r\lesssim\;$50kpc), the cluster is hot ($\sim\;$9-10keV) and is almost isothermal for $r\lesssim 1$Mpc; the latter contradicts a previous study. We do not detect any variation of the redshift of the ICM in the cluster; the upper limit of the velocity difference is 3000kms$^{-1}$. The iron-line ratios in X-ray spectra indicate that the ICM has reached the ionization equilibrium state. From these results, we conclude that the Ophiuchus cluster is not a major merger cluster, but one of the hottest clusters with a cool core. We obtain the upper limit of non-thermal emission from the cluster, which is consistent with both the recent claimed detection with INTEGRAL and the recent upper limits with the Swift/BAT. If the cluster has bright non-thermal emission, as suggested by the INTEGRAL measurement, it is probably not due to a recent major cluster merger.