Observations of solar flare particle anisotropies from 1.0 to 4.7 AU

The anisotropy of protons produced by solar flare particle events has been studied using the University of Chicago Charged Particle Instruement Main Telescope on the Pioneer 10 and 11 spacecraft. The observations were made during 1972 ad 1973 and covered a range of solar radial distances of 1.0 to 4.7 AU. The Pioneer spacecraft rotate at a rate of about 5 RPM around a spin axis which lies in the ecliptic plane. The Main Telescope scans the sky at an angle of 700 to the spin axis. Counting rates and angular information are recorded and rates for each of eight 450-sectors are computed in ground processing. The anisotropy amplitude, delta, and phase,phi, is computed by fitting the function C0 (1 + delta cos(theta-phei)) to the eight sectored rates (C0 is the average rate). The resulting anisotropy amplitude is corrected for telemetry-induced distortions. Using a model of cosmic ray diffusion developed by Parker (1963) and Krimigis (1965) to analyze the anisotropy observations, it has been determined that the diffusion coefficient of 3 to 10 MeV protons travelling parallel to the magnetic field is: K11(r) = (9.78 +- 2.3) x 1021 r101+-024 cm2/sec where r is the radial distance in AU. The corresponding 3-dimensional radial diffusion coefficient is K/sub r3/(r) = (1.35 +- 0.32) x 1021 r-063+-024 cm2/sec. Comparison of these numbers with other experimental results is made, and theoretical implications are discussed. The dependence of the anisotropy on energy is investigated and is found to be the proportional 1/v, as predicted by diffusion theory, near the times of maximum flux in the flare, but at earlier and later times, it deviates from this dependence