On the source location of radiation belt relativistic electrons

Observations from the High Sensitivity Telescope (HIST) on Polar made around January and May 1998 are used to constrain the source location of outer radiation belt relativistic electrons. Phase space densities calculated as a function of the three adiabatic invariants show positive radial gradients for L < 4, suggestive of no source in that region. In particular, the peak intensity near L = 3 of a large enhancement beginning on May 4, 1998, appears to have been formed by inward transport over a period of several days. For L > 4, peaks in the radial dependence of the phase space density are suggestive of a local electron source that may be nonadiabatic acceleration or pitch angle scattering. However, discrepancies in the results obtained with different magnetic field models and at different local times make this a tentative conclusion.