Physics
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aps..apr.r2002l&link_type=abstract
American Physical Society, April Meeting, 2004, May 1-4, 2004, Denver, Colorado April 2004, MEETING ID: APR04, abstract #R2.002
Physics
Scientific paper
The Sun is the most energetic particle accelerator in the solar system, producing ions up to tens of GeV and electrons to hundreds of MeV in solar flares and fast Coronal Mass Ejections (CMEs). Solar flares are the most powerful explosions, releasing up to 10^3^2^-^3^3 ergs in 10-1000s. The accelerated ˜10-100 keV electrons and > ˜1 MeV ions often contain the bulk of this energy, indicating that the particle acceleration and energy release processes are intimately linked. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission (launched February 2002) provides the first high-resolution imaging (to ˜2 arcsec) and spectroscopy ( ˜ keV FWHM) of solar hard X-ray/gamma-ray continuum and gamma-ray lines, emitted by the flare-accelerated electrons and ions in bremsstrahlung and nuclear collisions with the solar atmosphere, respectively. In the 23 July 2002 flare, RHESSI resolved the narrow prompt de-excitation gamma-ray lines of Fe, Mg, Si, Ne, C, and O, for the first time. Mass-dependent red shifts of 0.1-0.8 % were measured, implying downward motion of the parent accelerated protons and alphas along magnetic field lines that are tilted toward the Earth by ˜40^o. RHESSI located the flare-accelerated ions for the first time through imaging of the 2.223 MeV neutron-capture gamma-ray line, showing that the ions interact near the optical flare. The centroid of this line emission is located 20+-6 arcsec from the centroids for the 0.3-0.5 and 0.7-1.4 MeV bands that are dominated by electron bremsstrahlung, indicating that the acceleration and/or propagation of the ions must differ from that of the electrons. Information on the spectrum and composition of the accelerated ions was also obtained from the narrow and broad gamma-ray lines. The implications for our present understanding of the particle acceleration and energy release processes in flares will be discussed.
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