XMM-Newton observations of the X-ray feature 1SAX J0617.1+2221 in the IC 443 supernova remnant are reported .
We resolve the structure of the nebula into a compact core with a hard spectrum of photon index \gamma = 1.63 ^ { +0.11 } _ { -0.10 } in the 2–10 keV energy range .
The nebula also has an extended ( \sim 8 \hbox { $ { } ^ { \prime } $ } \times 5 \hbox { $ { } ^ { \prime } $ } ) X-ray halo , much larger than the radio emission extension .
The photon index softens , following a linear scaling with distance from the centroid , similar to other known X-ray plerions .
The index range is compatible with synchrotron burn-off models .
All the observational evidence points toward a confirmation of the plerionic nature of the nebula , as recently suggested by a Chandra observation , but with characteristics more similar to “ non Crab-like ” plerions .
We discuss the implications on the synchrotron nebula magnetic field if the > 100 MeV emission reported by CGRO EGRET is produced by the synchrotron emission .
We also constrain the thermal emission of the central object , arguing that the surface temperature should be around 0.1 keV , although other possible fits can not be excluded on the base of the XMM-Newton data .