Probing Ion Acceleration and Ambient Abundances in Solar Flares with RHESSI

Details Probing Ion Acceleration and Ambient Abundances in Solar Flares with RHESSI Probing Ion Acceleration and Ambient Abundances in Solar Flares with RHESSI

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11a..02s&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH11A-02

Physics

2118 Energetic Particles, Solar, 2194 Instruments And Techniques, 2451 Particle Acceleration

Scientific paper

Protons and heavier ions accelerated in solar flares to energies on the order of 1 MeV or more per nucleon can excite or even disrupt ambient nuclei in the solar atmosphere. These processes result in the emission during the flare of gamma-ray lines of characteristic energies. The ratios between the fluxes of different gamma-ray lines can reveal both the composition of the ambient medium and also the ratio between accelerated protons and alpha particles. Due to the recoil of the excited nuclei, the Doppler profiles of the de-excitation lines can be used to deduce the angular distribution of the accelerated ions as they interact. Accelerated nuclei heavier than helium produce very highly broadened lines from their own de-excitation after encountering ambient nuclei. These broad lines form a pseudo-continuum which, if carefully separated from the continuum due to electron bremsstrahlung, could provide a measure of the fraction of heavy nuclei in the accelerated population. I will review the results from two gamma-ray line flares observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on July 23, 2002 and June 17, 2003. These results include 1) the first subarcminute-resolution image of a gamma-ray line in a flare (revealing that the ions interact at a considerable distance from the electron bremsstrahlung site -- Hurford et al. 2003, ApJ Letters, in press), 2) the first energy-resolved spectra of the nuclear lines, showing their Doppler profiles (Smith et al. 2003, ibid), 3) significant and unexpected broadening of the positron annihilation line (Share et al. 2003, ibid), 4) a constraint on the photospheric 3He concentration from an analysis of the evolution of the line from neutron capture by hydrogen (Murphy et al. 2003, ibid), and 5) an apparent change in the ambient composition in the middle of the July 23 flare (Shih et al., in preparation).

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