Energetic Neutral Atoms from Solar Flares H. S. Hudson 1, R. P. Lin 1, A. L. MacKinnon 2, J. C....
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Transcript of Energetic Neutral Atoms from Solar Flares H. S. Hudson 1, R. P. Lin 1, A. L. MacKinnon 2, J. C....
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Energetic Neutral Atoms from Solar Flares
H. S. Hudson1, R. P. Lin1, A. L. MacKinnon2,
J. C. Raymond3, A. Y. Shih1, and Wang, L.1
1University of California, Berkeley; 2University of Glasgow (UK),
3Institute for Astronomy, Cambridge (US)
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SPD 2009
Overview
• Mewaldt et al. (2009)* have observed ENAs from a flare for the first time.
• This was unexpected but highly significant - it reveals a virtually unknown parameter space (flare-associated protons below a few MeV).
• The flare ENAs could come from the CME shock acceleration, or from the flare -ray sources.
• We are studying the ENA sources by Monte Carlo techniques.
*ApJ 693, L11 (2009)
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SPD 2009
Mewaldt et al. Figures
• The STEREO observations provide both spatial and temporal signatures that clearly identify the particles as hydrogen• The injection times closely match the GOES light curve of the flare
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SPD 2009
How many particles?• Mewaldt et al. estimate a total of 1.8 x 1028 ENA
particles (hydrogen atoms) assuming isotropic emission in a hemisphere
• RHESSI -ray observations imply a total of 1.3 x 1031 protons above 30 MeV
• Assuming a spectral index of 3.5, this implies a total of 2 x 1034 protons above 1.6 MeV
The escape efficiency of 2 MeV ENAsmay be of order 10-6
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SPD 2009
Whence flare ENAs?
Neutralization and re-ionization on open field lines: Mikic & Lee, 2006
Neutralization and re-ionization on closed field lines: Dennis & Schwartz, 1989
http://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/
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SPD 2009
Monte Carlo simulations• Neutral hydrogen and protons are alternative states
of the same particle. Can successive ionizations and neutralizations allow flare ENAs to originate from the flare -ray sources in the deep corona?
• If so, do the emergent ENAs retain any information about the spectrum, source structure, or time profile?
• Everything is very complicated, so we are trying to extract answers via Monte Carlo simulations embodying enough of the physics
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SPD 2009
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Proton injected at 1.2 Rsun @ 2 MeV (example)
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SPD 2009
What do we want to learn from the Monte Carlo model?
• The escape efficiency as a function of injection height and other parameters
• The spectrum of the escaping ENAs, ditto• The angular distribution of the emerging ENAs• The spatial structure of the apparent ENA source
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SPD 2009
Conclusions
• The Mewaldt et al. (2009) result is one of the most important for flare high-energy physics in this century, since it opens a vast new parameter space
• Interpretation is wide open at present. Our Monte Carlo model suggests that ENA escape from the flare -ray sources may be feasible, but it is preliminary work
• If the ENAs come from CME shock acceleration, we will need to revise our views of where this is happening
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SPD 2009
Backup slides
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SPD 2009
Mewaldt et al. Figures (II)
• The HET counts resemble those expected from neutron decay• The LET spectrum appears to steepen > 5 MeV
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SPD 2009
Some necessary physics
• Charge exchange vs collisions• Charge exchange cross-sections (H-like and He-like only)
Fe?
• Impact ionization i = 2.3 x 10-17 Ep-0.897 cm2 (Barghouty, 2000)
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Fe?
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SPD 2009
Notes on Monte Carlo model• The calculation includes ion flight with RK4 tracing of
the guiding center in a Schrijver-DeRosa PFSS model of the coronal field (Hudson et al., 2009)
• Ion dE/dx from Weaver & Westphal (2003); ion stripping from Barghouty (2000); charge-exchange on K-shell minor ions from Kuang (1992); ionization equilibrium from Mazzotta
• The plots show successive ion and neutral flights (red) for a few particles with different fates
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SPD 2009
QuickTime™ and aTIFF (Uncompressed) decompressor
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QuickTime™ and aTIFF (Uncompressed) decompressor
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QuickTime™ and aTIFF (Uncompressed) decompressor
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QuickTime™ and aTIFF (Uncompressed) decompressor
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1. Energy decay3. Time out
2. Footpoint ENA flight4. Solar wind ENA flight
Protons injected at 1.2 Rsun @ 2MeV (examples)