Thermal and Nonthermal Nature of the Soft Excess Emission from Sérsic 159-03 Observed with XMM-Newton

Several nearby clusters exhibit an excess of soft X-ray radiation that cannot be attributed to the hot virialized intracluster medium. There is no consensus to date on the origin of the excess emission: it could be either of thermal origin or due to an inverse Compton scattering of the cosmic microwave background. Using high-resolution XMM-Newton data of Sérsic 159-03 we first show that strong soft excess emission is detected out to a radial distance of 0.9 Mpc. The data are interpreted using the two viable models available, i.e., by invoking either a warm reservoir of thermal gas or relativistic electrons that are part of a cosmic-ray population. The thermal interpretation of the excess emission, slightly favored by the goodness-of-fit analysis, indicates that the warm gas responsible for the emission is high in mass and low in metallicity.