Properties of the Intracluster Medium of Abell 3667 Observed with Suzaku XIS

Abstract

We observed the northwest region of the cluster of galaxies Abell 3667 with the Suzaku XIS instrument. The temperature and surface brightness of the intracluster medium were measured up to the virial radius (r₂₀₀ ∼ 2.3 Mpc). The radial temperature profile is flatter than the average profile for other clusters until the radius reaches the northwest radio relic. The temperature drops sharply from 5 keV to about 2 keV at the northwest radio relic region. The sharp changes of the pressure can be interpreted as a shock with a Mach number of about 1.9. The entropy slope becomes flatter in the outer region and negative around the radio relic region. In this region, the relaxation timescale of electron-ion Coulomb collisions is longer than the time elapsed after shock heating, and the plasma may be out of equilibrium. Using differential emission measure (DEM) models, we also confirmed the multi-temperature structure around the radio relic region, characterized by two peaks at 0.9 keV and 4.0 keV. These features suggest that the gas is heated by a shock propagating from the center to the outer region.