Acceleration of energetic protons by interplanetary shocks

The University of Iowa instrument aboard Pioneer 11 detected 69 energetic proton events (EPE) (0.6< or =E/sub p/< or =3.4 MeV) during 1973--1974 in the heliocentric radial range 1--5 AU. Sixty percent of the EPE peak within +- 5 hours of a corotating interaction region (CIR) boundary, while 19% peak inside and 21% peak outside the interaction regions. Of the CIR boundaries at which an EPE peaks within +- 5 hours, 80% have associated shocks. The observed intensities and pitch angle distributions of protons near shock fronts are consistent with a theoretical similation of the acceleration of protons by a del vertical-bar B vertical-bar drift in a V x B electric field at the shock front