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G.H. Share, R.J. Murphy (NRL), R. Ramaty (NASA GSFC), B. Kozlovsky (Tel Aviv Univ.)
Gamma-ray spectra of solar-flare emissions contain bremsstrahlung, neutron-capture and e+e- annihilation lines, nuclear de-excitation lines from ambient elements excited by proton and \alpha-particle interactions, and de-excitation lines from energetic heavy ions that impact ambient H and He. Lines from the energetic heavy ions are expected to be Doppler broadened and, perhaps shifted, reflecting the transport of these particles. These lines provide the only source of information on the composition of accelerated heavy ions at the Sun. There are already indications for heavy-ion abundance enhancements for two flares, 1981 April 27 and 1991 June 1. In the current study we utilize spectral data from both the Solar Maximum Mission Gamma Ray Spectrometer and the Compton Gamma Ray Observatory (CGRO) OSSE instrument to reveal the broad-line spectra of flares and thus allow direct measurement of the abundances of energetic heavy ions at the Sun. We do this by stripping away the contributions of bremsstrahlung, de-excitations from ambient elements, n-capture, and e+e- annihilation from the measured spectra. The residual spectrum contains individual strong broadened lines, as well as a `continuum' from a multitude of weaker features. The latter is subtracted using calculations based on an assumed heavy-ion composition; the shape of this `continuum' does not vary significantly with composition, however. This process has resulted in the first separated \gamma-ray spectra from accelerated heavy ions at the Sun and shows clear broadened lines that can be compared with models to determine the ion abundance and transport during flares. We plan to exploit future observations of flares with CGRO/OSSE to make the first comparisons of accelerated heavy ions at the Sun with impulsive solar energetic particles as measured by the ACE Solar Isotopic Spectrometer.
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