Suzaku observation of the Ophiuchus galaxy cluster: One of the hottest cool core clusters

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 ≲ 50kpc), the cluster is hot (∼ 9-10 keV) and is almost isothermal for r ≲ 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 3000 km s-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. © 2008. Astronomical Society of Japan.