Energetic neutral atoms from solar flares H. S. Hudson SSL, UC Berkeley

Berkeley April 9, 2009 Background Mewaldt et al. (2009)* have observed ENAs from a flare for the first time. REVIEW This was unexpected but has enormous significance for flare physics. EXPLAIN Flare ENAs may have a strong association with the observed  -rays. SPECULATE *ApJ 693, L11 (2009) - no citations yet!

Berkeley April 9, 2009 Mewaldt et al. Figures (I)

Berkeley April 9, 2009 Mewaldt et al. Figures (II) The HET counts resemble those expected from neutron decay The LET spectrum appears to steepen > 5 MeV

Berkeley April 9, 2009 Where do flare ENAs come from? Neutralization and re-ionization on open field lines: Mikic & Lee, 2006 Neutralization and re-ionization on closed field lines: Dennis & Schwartz,

Berkeley April 9, 2009 Some necessary physics Charge exchange vs collisions Charge exchange cross-sections (H-like and He-like only) Fe?

Berkeley April 9, 2009 Neutralization and propagation Below about 1.6 R sun re-ionization is likely to occur. Above 1.6 R sun charge exchange is unlikely Mirroring energetic ions in closed-field regions (ie, the  -ray sources) can readily neutralize Escape from the deep corona may be possible by multiple neutralization/reionization events We are studying the latter option. Most of the lifetime of a particle is spent as an ion, and so this may erase most of the information about source structure

Berkeley April 9, 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 an entirely new channel Conditions need to be right for a successful observation, but it is likely that many more events could be detected Interpretation is wide open at present