AAS 204th Meeting, June 2004
Session 47 When the Sun Went Wild
Topical Session, Tuesday, June 1, 2004, 2:30-4:00pm, 4:15-6:00pm, 702/704/706

## [47.07] Gamma-Ray Spectroscopy & Imaging - What We Learn About Flares From High-Energy Ions

G.H. Share, R.J. Murphy (NRL), G.J. Hurford, R.P. Lin, A.Y. Shih (SSL/UCB), D.M. Smith (UCSC), R.A. Schwartz (NASA/GSFC)

The 2004 Oct. 28 and Nov. 2 flares were the most prolific emitters of nuclear gamma-rays observed by {\em RHESSI}, with measured fluences >1900 and ~ 900 \gamma cm-2, respectively. The Oct. 28 event was the brightest gamma-ray flare detected in over 20 years. We discuss measurements of nuclear de-excitation lines from Fe, Mg, Ne, Si, C, and O that provide information on the directionality of accelerated particles and the composition of the flare plasma where they interact. A strong narrow \gamma-ray line is emitted when neutrons produced by similar interactions are captured in the photosphere by H. We have imaged this capture-line and resolved a double source with components located on opposite sides of the post-flare arcade observed by {\em TRACE} in the Oct. 28 flare. We also discuss {\em RHESSI} images of the Oct. 29 and Nov. 2 flares. The positron-electron annihilation line and continuum provide information on the temperature and density near where the ions interact. The 511 keV line observed by {\em RHESSI} in the 2002 July 23 flare had a Gaussian width of 8.1 ± 1.1 keV FWHM, consistent with ~(4-7) \times 105K, if the broadening is thermal. The annihilation lines observed early in the Oct. 28 and Nov. 2 flares are also broadened: ~5.5 and ~6.5 keV FWHM, respectively. The lack of a strong positronium continuum suggests that the lines are broadened thermally in an ionized medium at ~1014 H cm-3. The line narrows significantly to ~1 keV later in the Oct. 28 flare, suggestive of a significant drop in temperature. This work was supported by NASA DPR W19746/10049 at NRL and by NAS 5-98033 at UCB and GSFC.