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Observational and theoretical evidence suggests that high-energy Galacticcosmic rays are primarily accelerated by supernova remnants. If also true forlow-energy cosmic rays, the ionization rate near a supernova remnant should behigher than in the general Galactic interstellar medium (ISM). We have searchedfor H3+ absorption features in 6 sight lines which pass through molecularmaterial near IC 443---a well-studied case of a supernova remnant interactingwith its surrounding molecular material---for the purpose of inferring thecosmic-ray ionization rate in the region. In 2 of the sight lines (toward ALS8828 and HD 254577) we find large H3+ column densities, N(H3+)~3*10^14 cm^-2,and deduce ionization rates of zeta_2~2*10^-15 s^-1, about 5 times larger thaninferred toward average diffuse molecular cloud sight lines. However, the 3sigma upper limits found for the other 4 sight lines are consistent withtypical Galactic values. This wide range of ionization rates is likely theresult of particle acceleration and propagation effects, which predict that thecosmic-ray spectrum and thus ionization rate should vary in and around theremnant. While we cannot determine if the H3+ absorption arises in post-shock(interior) or pre-shock (exterior) gas, the large inferred ionization ratessuggest that IC 443 is in fact accelerating a large population of low-energycosmic rays. Still, it is unclear whether this population can propagate farenough into the ISM to account for the ionization rate inferred in diffuseGalactic sight lines.

Investigating the Cosmic-Ray Ionization Rate Near the Supernova Remnant IC 443 Through H3+ Observations