AWM 4 - an isothermal cluster observed with XMM-Newton

We present an analysis of an XMM-Newton observation of the poor cluster AWM 4. The cluster is relaxed and its X-ray halo is regular with no apparent substructure. Azimuthally averaged radial spectral profiles suggest that the cluster is isothermal to a radius of at least 160 kpc, with no evidence of a central cooling region. Spectral mapping shows some significant temperature and abundance substructure, but no evidence of strong cooling in the cluster core. Abundance increases in the core, but not to the extent expected, and we find some indication of gas mixing. Modelling the three-dimensional properties of the system, we show that ongoing heating by an active galactic nuclei (AGN) in the dominant elliptical, NGC 6051, is likely to be responsible for the lack of cooling. We also compare AWM 4 to MKW 4, a cluster of similar mass observed recently with XMM-Newton. While the two systems have similar gravitational mass profiles, MKW 4 has a cool core and a somewhat steeper gas density profile, which leads to a lower core entropy. AWM 4 has a considerably larger gas fraction at 0.1R₂₀₀, and we show that these differences result from the difference in mass between the two dominant galaxies and the activity cycles of their AGN. We estimate the energy required to raise the temperature profile of MKW 4 to match that of AWM 4 to be 9 × 10⁵⁸ erg or 3 × 10⁴³ erg s^-1 for 100 Myr, comparable to the likely power output of the AGN in AWM 4.