XMM-Newton observations of the Perseus cluster - II. Evidence for gas motions in the core

The 5-9 keV spectrum of the inner ~100 kpc of the Perseus cluster measured by XMM-Newton can be well described by an optically thin plasma emission model as predicted by the APEC code, without any need for invoking a strong Ni overabundance or the effects of resonant scattering. For the strongest 6.7-keV line of He-like iron, the optical depth of the cluster, calculated using observed density, temperature and abundance profiles, is of the order of 3. The lack of evidence for resonant scattering effects implies gas motion in the core with a range in velocities of at least half of the sound velocity. If this motion has the character of small-scale turbulence, then its dissipation would provide enough energy to compensate for radiative cooling of the gas. The activity of the supermassive black hole at the centre of the cluster may be the driving force of the gas motion.