34th Solar Physics Division Meeting, June 2003
Session 14 RHESSI Results I
Oral, Wednesday, June 18, 2003, 9:00am-12:00noon, Auditorium

## [14.08] High-Resolution Observation of the Solar Positron-Electron Annihilation Line

G.H. Share, R.J. Murphy, J.G. Skibo (NRL), D.M. Smith, H.S. Hudson, R.P. Lin, A.Y. Shih (SSL/UCB), R.A. Schwartz (NASA GSFC), B Kozlovsky (Tel Aviv Univ.)

RHESSI has observed the positron-electron annihilation line at 511 keV produced during the 2002 July 23 solar flare. The shape of the line is consistent with annihilation in two vastly different solar environments. It can be produced by formation of positronium by charge exchange in flight with hydrogen in a quiet solar atmosphere at a temperature of ~6000 K. However, the measured upper limit to the 3\gamma/2\gamma ratio (ratio of annihilation photons in the positronium continuum to the number in the line) is only marginally consistent with what is calculated for this environment. The annihilation line can also be fit by a thermal Gaussian having a width of 8.1 ±1.1 keV (FWHM), indicating temperatures of ~4 - 7 \times 105 K. The measured 3\gamma/2\gamma ratio does not constrain the density when the annihilation takes place in such an ionized medium, however the density must be high enough to slow down the positrons. This would require the formation of a substantial mass of atmosphere at transition-region temperatures during flares.