Transcript osu2010_ic443_uploaded.ppt

Constraining the Flux of LowEnergy 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
FC10; June 25, 2010
Image credit: Gerhard Bachmayer
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
12CO
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 0.3-0.5 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
  
0
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
 2 n(H 2 )  ke ne n(H )

3
Calculating the Ionization Rate
 2 n(H 2 )  ke ne n(H )

3
N(H2) from N(CH)

3
N (H )
 2  ke ne
N (H 2 )

3
N (H )
 2  ke xe nH
N (H 2 )
xe from C+;
Cardelli et al. 1996, ApJ, 467, 334
Sheffer et al. 2008, ApJ, 687, 1075
nH from C2 and CN;
Hirschauer et al. 2009, ApJ, 696, 1533
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
Observations
HD 43703
ALS 8828
HD 254755
HD 43582
HD 254577
HD 43907
Results
HD 43703
ALS 8828
HD 254755
HD 43582
HD 254577
HD 43907
Results
N(H3+)
(1014 cm-2)
ALS 8828
HD 254577
HD 254755
4.4
2.2
< 0.6
HD 43582
HD 43703
HD 43907
< 0.8
< 0.6
< 2.1

3
N (H ) 
 2 N (H 2 )
ke xe nH
ζ2
(10-16 s-1)
16±10
26±15
< 3.5
< 9.0
< 5.7
< 40
Either ζ2 is large,
or xenH is small
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
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
Spitzeret&al.
Torres
Tomasko
2008, MNRAS,
1968, ApJ,
387,152,
L59971
<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
Conclusions
• We’ve detected large columns of H3+ in 2
sight lines toward IC 443
• This is either the result of a high cosmicray 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 H3+ toward other supernova
remnants which are interacting with
molecular clouds; e.g. W 44, W 28, W 51