On the metal abundances inside mixed-morphology supernova remnants: the case of IC 443 and G166.0+4.3

Context. Recent developments in the study of mixed morphology supernova remnants (MMSNRs) have revealed the presence of metal-rich X-ray emitting plasma inside a fraction of these remnants, a feature not properly addressed by traditional models for these objects. Aims. Radial profiles of thermodynamical and chemical parameters are needed for a fruitful comparison of data and model of MMSNRs, but these are available only in a few cases. Methods. We analyzed XMM-Newton data of two MMSNRs, namely IC 443 and G166.0+4.3, previously known to have solar metal abundances, and performed a spatially resolved spectral analysis of the X-ray emission. Results. We detected enhanced abundances of Ne, Mg and Si in the hard X-ray bright peak in the north of IC 443, and of sulphur in the outer regions of G166.0+4.3. The metal abundances are not distributed uniformly in both remnants. The evaporating clouds model and the radiative SNR model fail to reproduce consistently all the observational results. Conclusions. We suggest that further deep X-ray observations of MMSNRs may reveal more metal-rich objects. More detailed models including ISM-ejecta mixing are needed to explain the nature of this growing subclass of MMSNRs.