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

TL;DR

This study analyzes Suzaku X-ray data of the Ophiuchus galaxy cluster, confirming it as a hot, cool-core cluster with specific temperature and metallicity profiles, and discusses its dynamical state and non-thermal emission limits.

Contribution

First detailed Suzaku analysis confirming the Ophiuchus cluster's cool core and high temperature, challenging previous findings and constraining non-thermal emission.

Findings

The cluster has a cool core with decreasing temperature towards the center.

The ICM is almost isothermal (~9-10 keV) outside the core.

No significant velocity variation detected in the ICM.

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<~50 kpc), 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 the 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.