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Constraining the Flux of Low-Energy Cosmic Rays Accelerated by the Supernova Remnant IC 443

Constraining the Flux of Low-Energy Cosmic Rays Accelerated by the Supernova Remnant IC 443. N. Indriolo 1 , G. A. Blake 2 , M. Goto 3 , T. Usuda 4 , T. R. Geballe 5 , T. Oka 6 , & B. J. McCall 1. 1 – University of Illinois at Urbana-Champaign 2 – California Institute of Technology

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Constraining the Flux of Low-Energy Cosmic Rays Accelerated by the Supernova Remnant IC 443

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  1. Constraining the Flux of Low-Energy Cosmic Rays Accelerated by the Supernova Remnant IC 443 N. Indriolo1, G. A. Blake2, M. Goto3, T. Usuda4, T. R. Geballe5, T. Oka6, & B. J. McCall1 1 – University of Illinois at Urbana-Champaign 2 – California Institute of Technology 3 – Max Planck Institute for Astronomy 4 – Subaru Telescope 5 – Gemini Observatory 6 – University of Chicago Image credit: Gerhard Bachmayer

  2. Why look near supernova remnants? • Observational evidence suggests Galactic cosmic rays are accelerated primarily by supernova remnants (SNRs) • As cosmic rays propagate, they interact with the ISM • excitation & ionization of atoms & molecules • excitation of nuclear states • spallation of ambient nuclei • production of pions (0, +, -)

  3. IC 443 Basics • Located at (l,b)=(189°,+3°) • 1.5 kpc away in Gem OB1 association • Estimated to be about 30,000 years old • Known to be interacting with surrounding molecular material • Lies behind a quiescent molecular cloud

  4. IC 443 tour: Radio to Gamma-Rays Troja et al. 2006, ApJ, 649, 258

  5. IC 443 tour: Radio to Gamma-Rays 12CO antenna temperature map: Dickman et al. 1992, ApJ, 400, 203

  6. IC 443 tour: Radio to Gamma-Rays 2MASS JHK bands: Rho et al. 2001, ApJ, 547, 885

  7. IC 443 tour: Radio to Gamma-Rays XMM 0.3-0.5 keV X-ray map: Troja et al. 2006, ApJ, 649, 258

  8. IC 443 tour: Radio to Gamma-Rays VERITAS gamma-ray map: Acciari et al. 2009, ApJ, 698, L133

  9. H3+ Chemistry • Formation • CR + H2 H2+ + e- + CR’ • H2+ + H2  H3+ + H • Destruction • H3+ + e-  H2 + H or H + H + H (diffuse cloud) • H3+ + CO  H2 + HCO+ (dense clouds) • Steady state

  10. N(H2) from N(CH) Sheffer et al. 2008, ApJ, 687, 1075 Calculating the Ionization Rate xe from C+; Cardelli et al. 1996, ApJ, 467, 334 nH from C2 and CN; Hirschauer et al. 2009, ApJ, 696, 1533

  11. Observations • Transitions • H3+ν2 0 • R(1,1)u, R(1,0), R(1,1)l, Q(1,0), Q(1,1), R(3,3)l • Telescopes • Keck: NIRSPEC • Subaru: IRCS • 6 target sight lines with CH & CN

  12. HD 43703 ALS 8828 HD 254755 HD 43582 HD 254577 HD 43907 Observations

  13. Results

  14. HD 43703 ALS 8828 HD 254755 HD 43582 HD 254577 HD 43907

  15. Either ζ2 is large, or xenH is small Results

  16. Case 1: Low electron density • By taking an average value from C+, have we overestimated the electron density? • xe decreases from ~10-4 in diffuse clouds to ~10-8 in dense clouds • C2 rotation-excitation and CN restricted chemical analyses indicate densities of 200-400 cm-3 (Hirschauer et al. 2009) • Estimated values of x(CO) are ~10-6, much lower than 3×10-4 solar system abundance of carbon

  17. Case 2: High Ionization Rate • How can we explain the large difference between detections and upper limits? • Cosmic-ray spectrum changes as particles propagate • Perhaps ALS 8828 & HD 254577 sight lines probe clouds closer to SNR Spitzer & Tomasko 1968, ApJ, 152, 971 Torres et al. 2008, MNRAS, 387, L59

  18. 7.5 pc <5.710-16 s-1 1610-16 s-1 <3.510-16 s-1 <9.010-16 s-1 2610-16 s-1 <4010-16 s-1

  19. Conclusions • We’ve detected large columns of H3+ in 2 sight lines toward IC 443 • This is either the result of a high cosmic-ray ionization rate or low electron density • Unclear whether or not low-energy cosmic rays accelerated by SNRs can account for the flux necessary in the Galactic ISM to produce the inferred ionization rate

  20. Future Work • Use COS on Hubble to observe C II, C I, and CO absorption toward IC 443 • Search for H3+ toward other supernova remnants which are interacting with molecular clouds; e.g. W 44, W 28, W 51

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