HEAD 2003 Meeting
Session 33. Protostars, Stars and Instrumentation II
Oral, Monday, March 24, 2003, 4:30-5:30pm

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[33.03] RHESSI Spectroscopy and Imaging of Solar Gamma-ray Lines

D. M. Smith, G. J. Hurford (U. C. Berkeley), G. H. Share, R. J. Murphy (Naval Research Laboratory), R. A. Schwartz (NASA/Goddard), A. Y. Shih, R. P. Lin (U. C. Berkeley)

The observation of the X-class solar flare of July 23, 2002 by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) marks a turning point in the study of ion acceleration in solar flares. For the first time we have fully resolved the nuclear de-excitation lines of C, O, Mg, Ne, Si and Fe, using RHESSI's high-resolution germanium detectors. These lines show surprisingly high redshifts considering the heliocentric angle of the flare (73 deg), implying either that the loop containing the ions is somewhat flattened against the solar surface or that the ions are beamed along the field.

Also for the first time, we have imaged the line emission on the Solar disk, with a resolution of 35 arcsec in the 2.2 MeV line from neutron capture and 3 arcmin in the C/O line complex from 4-7 MeV. We find a significant offset between the hard x-ray emission from the flare (nonthermal electron bremsstrahlung) and the 2.2 MeV emission.

Finally, the first resolved spectrum of a solar positron-annihilation line shows a broad component, with FWHM around 5-6 keV. This component could be created by annihilation in a plasma of approximately 200,000-300,000 K stirred up by the flare (there is little material at this temperature in the undisturbed atmosphere), or else via positronium formation in a nearly neutral environment (which would require the positrons to penetrate to the photosphere or lower chromosphere).

We will review these and other results from this flare. This work is supported by NASA contract NAS5-98033 and NASA DPR W19746.

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Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.