Interplanetary acceleration of relativistic electrons observed with Imp 7

The intensities of 0.22- to 0.5-MeV and 0.5- to 0.8-MeV electrons in interplanetary space following the October 29, 1972, solar particle event have been observed with the JHU/APL experiment aboard the Imp 7 satellite. Intensity variations associated with the ssc disturbance of 1655 UT on October 31 are interpreted as suggesting interplanetary acceleration. The results are consistent with an energy-dependent acceleration process, which is most effective for electrons of ∼0.4 MeV. This is the first reported interplanetary shock wave acceleration of relativistic electrons of which we are aware.