Soft X-ray structure of the Perseus cluster of galaxies

Abstract

A 0.5-1.5 keV X-ray image of the Perseus cluster of galaxies was obtained with a focusing telescope system aboard a sounding rocket. The source consists of a region of diffuse emission plus a superposed central source in the vicinity of NGC 1275 smaller than 4' in diameter that accounts for one-quarter of the total intensity within a radius of 25'. Our results for the diffuse source are consistent with the isothermal-hydrostatic picture in which the hot gas has a core radius of 17' and is approximately symmetric about NGC 1275. We consider several isothermal-hydrostatic models relating the size and temperature of the diffuse X-ray source with the core radius of the galaxies and their velocity dispersion. Fixing the velocity dispersion at values measured by Chincarini and Rood requires the core radius of the galaxies to be 28' ± 9', which is larger than present measurements. Conversely, fixing the core radius of the galaxies at 8' (Bahcall) requires a smaller velocity dispersion or a condition in which the velocity distribution is anisotropic. Upper limits on the intrinsic X-ray absorption of the central source place the bulk of its X-ray emission beyond the nuclear region of NGC 1275.