The Shock Structure of Supernova Remnant IC443

We present and discuss ISO observations of IC443, a supernova remnant interacting with a molecular cloud. An SWS spectrum centered on molecular hydrogen clump R10E (RA(2000) = 6 17 7.6, Decl(2000) = 22 25 34.6) is dominated by strong [SiII] (34 microns) emission and the pure rotational transitions of molecular hydrogen ranging from 0-0 S(1) to 0-0 S(13). Fits to these H$-2$ lines imply a large column (approx. 7E19 cm$ {-2)$) of warm (T approx. 700 K) gas and an ortho/para ratio for hydrogen near 3. LWS Fabry-Perot spectra of [OI] (63 microns) and [CII] (158 microns) at positions R10E and C (RA(2000) = 6 17 42.8, Decl(2000) = 22 21 38.1) find broad (approx. 75 km/s), blue-shifted (-40 km/s) line profiles; their similarity strongly suggests a common, shock-generated origin for these two lines. The surprisingly large [CII]/[OI] ratio (approx. 0.1 to 0.2) confirms previous observations with the Kuiper Airborne Observatory. These [CII] and [OI] line intensities, the [SiII] intensity (above), and LWS grating measurements of OH (119 microns) and [OI] (145 microns) are all readily fit by a single, fast J-shock model. Although the [OI] (63) emission can alternatively be produced by a slow C-shock, this ensemble of lines can not be produced by such a shock and provides strong evidence for the existence of a J-shock. A 24-arcmin strip map shows that this far-infrared line emission is spatially correlated with the H$-2$ 1-0 S(1) emission, which most likely arises in an associated C-shock. In addition to this spatially correlated shock emission, the strip map identifies extended [CII] and [OI] emission with a significantly larger line ratio (approx. 0.6); this 'background' component is compared with current J-shock, C-shock, photo-dissociation region (PDR), and X-ray dissociation region (XDR) models in an effort to explain its origin.