Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009arep...53.1059c&link_type=abstract
Astronomy Reports, Volume 53, Issue 11, pp.1059-1069
Astronomy and Astrophysics
Astronomy
Solar Electromagnetic Emission, Solar Irradiance, Particle Emission, Solar Wind, Solar Wind Plasma, Sources Of Solar Wind, Energetic Particles
Scientific paper
Studies of the extreme solar proton event of January 20, 2005 intensified the contest over of a long-standing problem: are solar cosmic rays arriving at the Earth accelerated by solar flares or by shocks preceding rapidly moving coronal mass ejections? Among the most important questions is the relationship between the energy spectra of the solar cosmic rays and the frequency spectra of flare microwave bursts. Some studies of previous solar-activity cycles have shown that such a relationship does exist, in particular, for protons with energies of tens of MeV. The present work analyzes this relation using data for 1987-2008. For flare events observed in the western half of the disk, there is a significant correlation between the index δ, which is equivalent to the power-law index of the integrated energy spectrum of 10-100 MeV protons detected near the Earth’s orbit, and radio burst parameters such as a ratio of peak fluxes S at two frequencies (for example, at 9 and 15 GHz) and a microwave peak frequency f m . Proton fluxes with hard (flat) energy spectra ( δ ≤ 1.5) correspond to hard microwave frequency spectra ( S 9/ S 15 ≤ 1 and f m ≥ 15 GHz), while flares with soft radio spectra ( S 9/ S 15 ≥ 1.5 and f m ≤ 5 GHz) result in proton fluxes with soft (steep) energy spectra ( δ ≥ 1.5-2). It is also shown that powerful high-frequency bursts with the hardest radio spectra ( f m ≈ 30 GHz) can point at acceleration of significant proton fluxes in flares occurring in strong magnetic fields. These results argue that solar cosmic rays (or at least their initial impulses) are mainly accelerated in flares associated with impulsive and post-eruptive energy release, rather than in shocks driven by coronal mass ejections.
Chertok I. M.
Grechnev Victor V.
Meshalkina Natalia S.
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