The X-ray nebula of the filled center supernova remnant 3C 58 and its interaction with the environment

An XMM-Newton observation of the plerionic supernova remnant 3C 58 has allowed us to study the X-ray nebula with unprecedented detail. A spatially resolved spectral analysis with a resolution of 8 has yielded a precise determination of the relation between the spectral index and the distance from the center. We do not see any evidence for bright thermal emission from the central core. In contrast with previous ASCA and Einstein result, we derive an upper limit to the black-body 0.5-10 keV luminosity and emitting area of 1.8 10(32) erg s(-1) and 1.3 10(10) cm(2), respectively, ruling out emission from the hot surface of the putative neutron star an also excluding the outer- gap model for hot polar caps. We have performed for the first time a spectral analysis of the outer regions of the X-ray nebula, where most of the emission is still non-thermal, but where the addition of a soft (kT = 0.2-0.3 keV) optically thin plasma component is required to fit the spectrum at E < 1 keV. This component provides 6% of the whole remnant observed flux in the 0.5-10.0 keV band. We show that a Sedov interpretation is incompatible with SN 1181-3C 58 association, unless there is a strong deviation from electron-ion energy equipartition, and that an origin of this thermal emission in terms of the expansion of the nebula into ejecta core nicely fits all the radio and X-ray observations.