High-resolution observation of the solar positron-electron annihilation line

Gerald H. Share*, Ronald J. Murphy, Jeffrey G. Skibo, David M. Smith, Hugh S. Hudson, Robert P. Lin, Albert Y. Shih, Brian R. Dennis, Richard A. Schwartz, Benzion Kozlovsky

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


The Reuven Ramaty High Energy Solar Spectroscopic Imager (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 3γ/2γ 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 fitted by a thermal Gaussian having a width of 8.1 ± 1.1 keV (FWHM), indicating temperatures of ∼(4-7) × 105 K. The measured 3γ/2γ ratio does not constrain the density when the annihilation takes place in such an ionized medium, although 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 the flare.

Original languageEnglish
Pages (from-to)L85-L88
JournalAstrophysical Journal
Issue number2 II
StatePublished - 1 Oct 2003


FundersFunder number
National Aeronautics and Space AdministrationDPR W10049, DPR W19746
U.S. Naval Research Laboratory
School of Public Health, University of California BerkeleyNAS 5-98033
Israel Science Foundation


    • Sun: X-rays, gamma rays
    • Sun: flares
    • Sun: particle emission


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