A POSSIBLE SITE OF COSMIC-RAY ACCELERATION IN THE SUPERNOVA REMNANT IC-443

We present evidence for shock acceleration of cosmic rays to high ener gies (similar to 10 TeV) in the supernova remnant IC 443. X-ray imagin g spectroscopy with ASCA reveals two regions of particularly hard emis sion: an unresolved source embedded in an extended emission region, an d a ridge of emission coincident with the southeastern rim. Both featu res are located on part of the radio shell where the shock wave is int eracting with molecular gas, and together they account for a majority of the emission at 7 keV. Though we would not have noticed it a priori , the unresolved feature is coincident with one resolved by the ROSAT HRI. Because this feature overlaps a unique region of hat radio spectr al index (alpha < 0.24), has about equal light-crossing and synchrotro n loss times, and a power-law spectrum with a spectral index of alpha = 1.3 +/- 0.2, we conclude that the hard X-ray feature is synchrotron radiation from a site of enhanced particle acceleration. Evidence agai nst a plerion includes a lack of observed periodicity (the pulsed frac tion upper limit is 33%), the spectral similarity with the more extend ed hard region, the location of the source outside the 95% error circl e of the nearby EGRET source, the fact that it is nestled in a bend in the molecular cloud ring with which IC 443 is interacting, and the re quirement of an extremely high transverse velocity (greater than or eq ual to 5000 km s(-1)). We conclude that the anomalous feature is most likely tracing enhanced particle acceleration by shocks that are forme d as the supernova blast wave impacts the ring of molecular clouds.