A Hard Extended X-Ray Source in the IC 443 Supernova Remnant Resolved by Chandra: A Fast Ejecta Fragment or a New Pulsar Wind Nebula?

A Chandra observation of the isolated hard X-ray source XMMU J061804.3+222732, located in the region of the apparent interaction of the supernova remnant IC 443 with a molecular cloud, resolved the complex structure of the source in a few bright clumps embedded in an extended emission of ~30" in size. The X-ray spectra of the clumps and the extended emission are dominated by a hard power-law component with a photon index of 1.2-1.4. In addition, we see some indications of an optically thin thermal plasma of an ~0.3 keV temperature. The observed X-ray morphology and spectra are consistent with those expected for an isolated supernova ejecta fragment interacting with a dense ambient medium. A possible alternative interpretation is a pulsar wind nebula associated with either IC 443 or another supernova remnant, G189.6+3.3.