2008AJ....135..796L

We report 21 cm spectral-line and continuum observations of the Galactic supernova remnant IC 443 using the Very Large Array (VLA) and the Arecibo telescope. By combining the VLA and Arecibo data, both covering the full extent of IC 443, we have achieved an unprecedented combination of sensitivity and angular resolution, over the continuous range of angular scales from ∼40' to ∼1°. Our new radio observations not only reveal previously unknown features of IC 443 but also show the details of the remnant more clearly. The radio morphology of IC 443 consists of two nearly concentric shells. Our 21 cm radio continuum data show that the two shells have distinctly different radial intensity distributions. This morphology supports the scenario whereby the western shell is a breakout portion of the remnant into a rarefied medium. We have developed a dynamical model accounting for the breakout, which provides an estimate for the remnant age of ∼2x10⁴yr. The southeastern boundary of the remnant shows interesting features, seen in our observations for the first time: a faint radio continuum halo and numerous "spurs." These features are mainly found in the region where IC 443 overlaps with another remnant, G189.6+3.3. These features most likely originate from the interactions of IC 443 with the surrounding medium. The H I emission associated with IC 443 appears over the velocity range between -100 km.s^–1 and 50 km.s^–1. The strongest absorption is seen around v_LSR∼ -5 km.s^–1, which corresponds to the systemic velocity of IC 443. We identify a broad, extended lane of H I gas near the systemic velocity as preshock gas in the southern part of the remnant. Most of the shocked H I gas is located along the southern supernova remnant (SNR) boundary and is blueshifted. We derive an accurate mass of the shocked H I gas using template HCO⁺ (1-0) spectra, which is 493±56 M_☉. Our high-resolution H I data enable us to resolve the shocked H I in the northeastern region into a few filamentary structures, which are well correlated with radiative filaments, in both position and velocity. This represents the first unambiguous detection of the recombined H I in an atomic shock. The characteristics of the filaments are not consistent with a clumpy shock model where the radiative signature is from dense clumps. Instead we propose that the shock has been propagating through a uniform medium of n_H∼ 10 cm^–3.