PROTON ENERGY-SPECTRA AT THE SUN IN THE SOLAR COSMIC-RAY EVENTS ON 1978 MAY 7 AND 1984 FEBRUARY 16

The solar proton differential energy spectra at the Sun as a function of rigidity have been deduced for the solar cosmic-ray events on 1978 May 7 and 1984 February 16. Proton data were used from the IMP spacecraft for energies from about 20-500 MeV and from the worldwide network of neutron monitors for energies greater than 500 MeV. Since these events were characterized by essentially scatter-free propagation in the interplanetary medium, the solar proton energy spectra observed at Earth were extrapolated back to the Sun to obtain the source spectra. It was found that the relative solar proton spectra at the Sun varied with time. They could be fitted by dJ/dE = A × P-δ × exp (-P/P0), where δ is about 4-5 and P0 ≥ 5000 MV. These results are interpreted in terms of the diffusive coronal shock acceleration model of Ellison and Ramaty, obtaining shock sizes of ≳109 cm and shock compression ratios of 1.7-2.1. The solar energy spectra predicted by stochastic acceleration do not fit the relative proton energy spectra at the Sun for the two events considered.