HR: 11:00h
AN: SP42A-03    [Abstracts]
TI: RHESSI Positron-Electron Annihilation Line Observations
AU: * Share, G H
EM: gerald.share@nrl.navy.mil
AF: Naval Research Laboratory, Code 7652 4555 Overlook Ave., S.W., Washington, DC 20375 United States
AU: Murphy, R J
EM: murphy@ssd5.nrl.navy.mil
AF: Naval Research Laboratory, Code 7652 4555 Overlook Ave., S.W., Washington, DC 20375 United States
AU: Smith, D M
EM: dsmith@scipp.ucsc.edu
AF: Univ. of California at Santa Cruz, 1156 High St., Santa Cruz, CA 95064 United States
AU: Lin, R P
EM: boblin@ssl.berkeley.edu
AF: Univ. of California at Berkeley, Space Sciences Laboratory, Berkeley, CA 94720 United States
AU: Schwartz, R A
EM: richard.schwartz@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Code 682, Greenbelt, MD 20771 United States
AB: 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.
UR: http://heseweb.nrl.navy.mil/gamma/solar/share.html
DE: 7507 Chromosphere
DE: 7514 Energetic particles (2114)
DE: 7519 Flares
DE: 7529 Photosphere
DE: 7554 X rays, gamma rays, and neutrinos
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly