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.