Discovery of Diffuse X-ray Emission in 47 Tuc

Abstract

We present the results of a search for diffuse x-ray sources in a 65 ksec ROSAT PSPC exposure of 47 Tuc. There is faint, soft emission on the NE side of the cluster at a distance of 6 arcmin from the core. The location of this emission along the direction of proper motion of the cluster suggests that it might be due to a bow shock. We show that a simple shock model fits the observed luminosity and temperature. However, a bow shock can only form if the rotation of the halo gas at the height of 47 Tuc (z = 3.3 kpc) is small compared to the rotation of the galactic plane. Therefore this observation provides not only the first x-ray detection of hot gas in a globular cluster, but also constrains the dynamics of the halo gas. We also find two sources of diffuse x-ray emission to the NE of the cluster which are brighter and harder. We consider a variety of models for this emission, including thermal emission from a high velocity wind from a hot white dwarf, and propose that it is due to inverse Compton emission from acceleration in the bow shock of low energy cosmic ray electrons from the population of millisecond pulsars in the cluster.