On the source location of radiation belt relativistic electrons

Observations from the High Sensitivity Telescope (HIST) on Polar made aroun d January and May 1998 are used to constrain the source location of outer r adiation 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, appea rs to have been formed by inward transport over a period of several days. F or L > 4, peaks in the radial dependence of the phase space density are sug gestive of a local electron source that may be nonadiabatic acceleration or pitch angle scattering. However, discrepancies in the results obtained wit h different magnetic field models and at different local times make this a tentative conclusion.