RHESSI Positron-Electron Annihilation Line Observations

Details RHESSI Positron-Electron Annihilation Line Observations RHESSI Positron-Electron Annihilation Line Observations

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp42a..03s&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #SP42A-03

Physics

7507 Chromosphere, 7514 Energetic Particles (2114), 7519 Flares, 7529 Photosphere, 7554 X Rays, Gamma Rays, And Neutrinos

Scientific paper

We discuss our analysis of the electron-positron annihilation line and continuum from flares observed by RHESSI. RHESSI observed what appears to be a thermally broadened line (~6.5 keV FWHM) at 511 keV over the first 10 min of the 2003 October 28 flare that was consistent with emission from a plasma >105 K. The line narrowed to a width of ~1 keV over the next 2 min. The narrow width suggests emission from a <104 K region that is at least 20% ionized. This suggests a rapid variation in the solar atmosphere at densities <1014 H cm-3. In contrast the shape of the annihilation line from the first ten minutes of the 2003 November 2 flare is consistent with emission from a quiet solar atmosphere at ~5200 K; however, the flux in the 3 γ continuum may be inconsistent with this location. RHESSI has recently observed gamma-ray emission from flares erupting from AR0720 on 2005 January 15, 17, 19, and 20. Our preliminary analysis of the January 20 flare reveals a gamma spectrum with a hard continuum, intense lines at 511 keV and 2223 keV (neutron capture), and relatively weak nuclear de-excitation lines. This gamma-ray spectrum is consistent with a very-hard accelerated particle spectrum that produces most of the positrons from decay of positive pi mesons produced near the photosphere. The annihilation line has a width of ~6.5 keV that is again suggestive of thermal broadening. This work has been supported by NASA DPR NNG04ED181 and by ONR.

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