FC10; June 25, 2010Image credit: Gerhard Bachmayer 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 3 – Max Planck Institute for Astronomy 4 – Subaru Telescope 5 – Gemini Observatory 6 – University of Chicago

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,  +,  - )

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

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

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

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

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

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

H 3 + Chemistry Formation –CR + H 2  H e - + CR’ –H H 2  H H Destruction –H e -  H 2 + H or H + H + H (diffuse cloud) –H CO  H 2 + HCO + (dense clouds) Steady state

Calculating the Ionization Rate x e from C + ; Cardelli et al. 1996, ApJ, 467, 334 n H from C 2 and CN; Hirschauer et al. 2009, ApJ, 696, 1533 Sheffer et al. 2008, ApJ, 687, 1075 N(H 2 ) from N(CH)

Observations Transitions –H 3 + ν 2  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

Observations HD HD HD HD HD ALS 8828

Results

HD HD HD HD HD ALS 8828

Results N(H 3 + )ζ2ζ2 (10 14 cm -2 )( s -1 ) ALS ±10 HD ±15 HD < 0.6< 3.5 HD 43582< 0.8< 9.0 HD 43703< 0.6< 5.7 HD 43907< 2.1< 40 Either ζ 2 is large, or x e n H is small

Case 1: Low electron density By taking an average value from C +, have we overestimated the electron density? x e decreases from ~10 -4 in diffuse clouds to ~10 -8 in dense clouds C 2 rotation-excitation and CN restricted chemical analyses indicate densities of 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

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 sight lines probe clouds closer to SNR Spitzer & Tomasko 1968, ApJ, 152, 971Torres et al. 2008, MNRAS, 387, L59

7.5 pc 16  s  s -1 <5.7  s -1 <3.5  s -1 <9.0  s -1 <40  s -1

Conclusions We’ve detected large columns of H 3 + 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

Future Work Use COS on Hubble to observe C II, C I, and CO absorption toward IC 443 Search for H 3 + toward other supernova remnants which are interacting with molecular clouds; e.g. W 44, W 28, W 51