The Disturbed 17 keV Cluster Associated with the Radio Galaxy 3C 438

TL;DR

This paper reports on Chandra X-ray observations of the galaxy cluster associated with radio galaxy 3C 438, revealing a large-scale gas disturbance likely caused by a major cluster merger or an energetic nuclear outburst, indicating an extreme event.

Contribution

First detailed analysis of the 17 keV cluster gas associated with 3C 438, identifying a large surface brightness discontinuity likely due to a major merger or powerful outburst.

Findings

Detected a 600 kpc surface brightness discontinuity in the cluster gas.

The energy required for the disturbance suggests a major merger rather than a nuclear outburst.

The cluster's high temperature may be due to gravitational mass or transient heating.

Abstract

We present results from a {\em Chandra} observation of the cluster gas associated with the FR II radio galaxy 3C 438. This radio galaxy is embedded within a massive cluster with gas temperature $\sim$17 keV and bolometric luminosity of 6$\times10^{45}$ ergs s$^{-1}$. It is unclear if this high temperature represents the gravitational mass of the cluster, or if this is an already high ($\sim$ 11 keV) temperature cluster that has been heated transiently. We detect a surface brightness discontinuity in the gas that extends $\sim$600 kpc through the cluster. The radio galaxy 3C 438 is too small ($\sim$110 kpc across) and too weak to have created this large disturbance in the gas. The discontinuity must be the result of either an extremely powerful nuclear outburst or the major merger of two massive clusters. If the observed features are the result of a nuclear outburst, it must be from an earlier epoch of unusually energetic nuclear activity. However, the energy required ($\sim10^{63}$ ergs) to move the gas on the observed spatial scales strongly supports the merger hypothesis. In either scenario, this is one of the most extreme events in the local Universe.