Observations of the flow pattern of low-energy galactic cosmic rays in the outer heliosphere

The Goddard/University of New Hampshire Cosmic-Ray Experiment on Pioneers 10 and 11 is capable of measuring the angular distribution in the azimuthal direction of low-energy galactic protons and helium nuclei over an energy range extending from 3-60 MeV. In 1977, Pioneer 10 was at the maximum heliocentric radial distance (14 AU) during the time that conditions of minimum modulation still prevailed at 1 AU. For this period, a first-order anisotropy of 7.4+-2% was detected flowing in a direction of 108+-160 for 30-56 MeV protons. A direction of 900 corresponds to the corotation direction, as well as that expected for particles flowing inward along the interplanetary field. For 30-56 MeV/nuc helium, a value of 5.6+-3% toward 147+-330 was measured. While no detectable flow (2.2+2.6%) was observed for anomalous helium in the 10-21 MeV/nuc range, this result is not in strong statistical disagreement with the proton observation