Field‐aligned electron bursts at high latitudes observed by OGO 4

In a series of passes in the northern high‐latitude region, short bursts of radiation were observed in the energy range 0.7 to 24 kev by detectors aboard the polar orbiting satellite OGO 4. Among these bursts were a number in which the pitch‐angle distributions at 2.3 kev displayed a maximum at small angles to the magnetic field lines. From the distributions and energy spectra it is argued that a possible source mechanism for these particles is electric fields parallel to the magnetic field lines at distances of several earth radii. The source particles would then be the ambient thermal plasma, with two markedly different temperature components, one at a few ev, from which the field‐aligned radiation originates, and the other greater than an order of magnitude hotter, which produces the isotropic portion of the pitch‐angle distribution.