INVESTIGATING THE COSMIC-RAY IONIZATION RATE NEAR THE SUPERNOVA REMNANT IC 443 THROUGH H{sup +}{sub 3} OBSERVATIONS ,
- Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)
- Division of Geological and Planetary Sciences and Division of Chemistry and Chemical Engineering, MS 150-21, California Institute of Technology, Pasadena, CA 91125 (United States)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, Heidelberg D-69117 (Germany)
- Subaru Telescope, 650 North A'ohoku Place, Hilo, HI 96720 (United States)
- Department of Astronomy and Astrophysics and Department of Chemistry, University of Chicago, Chicago, IL 60637 (United States)
- Gemini Observatory, 670 North A'ohoku Place, Hilo, HI 96720 (United States)
Observational and theoretical evidence suggests that high-energy Galactic cosmic rays are primarily accelerated by supernova remnants. If also true for low-energy cosmic rays, the ionization rate near a supernova remnant should be higher than in the general Galactic interstellar medium (ISM). We have searched for H{sup +}{sub 3} absorption features in six sight lines which pass through molecular material near IC 443-a well-studied case of a supernova remnant interacting with its surrounding molecular material-for the purpose of inferring the cosmic-ray ionization rate in the region. In two of the sight lines (toward ALS 8828 and HD 254577) we find large H{sup +}{sub 3} column densities, N(H{sup +}{sub 3}) {approx} 3 x 10{sup 14} cm{sup -2}, and deduce ionization rates of {zeta}{sub 2} {approx} 2 x 10{sup -15} s{sup -1}, about five times larger than inferred toward average diffuse molecular cloud sight lines. However, the 3{sigma} upper limits found for the other four sight lines are consistent with typical Galactic values. This wide range of ionization rates is likely the result of particle acceleration and propagation effects, which predict that the cosmic-ray spectrum and thus ionization rate should vary in and around the remnant. While we cannot determine if the H{sup +}{sub 3} absorption arises in post-shock (interior) or pre-shock (exterior) gas, the large inferred ionization rates suggest that IC 443 is in fact accelerating a large population of low-energy cosmic rays. Still, it is unclear whether this population can propagate far enough into the ISM to account for the ionization rate inferred in diffuse Galactic sight lines.
- OSTI ID:
- 21474461
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 724; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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