Near-Relativistic Electron c/v Onset Plots
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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It is often assumed that the first arriving electrons of a near-relativistic E 30 keV electron event are injected at the Sun impulsively and simultaneously at all observed energies and propagate scatter-free to 1 AU. In that case, a plot of the onset times T Omicron versus cv for various electron speeds v should yield the solar injection time T inj and the propagation distance D. In some electron events D-1.2 AU, but the inferred injection times are characteristically delayed by 10 minutes after the start of metricdecametric type III radio bursts believed to be signatures of electron injection. The delays may indicate electron injections not directly associated with the type III bursts, but the delays could also result from gradual or energy-dependent injections or from significant coronalinterplanetary electron scattering, even for well-beamed events. These effects could invalidate the cv plot analyses. We use Wind 3D Plasma and Energetic Particle 3DP electron data to make cv onset plots for 80 near-relativistic solar electron events to test for the consistency of the inferred values of D, which are found to be broadly distributed between 0.15 and 2.7 AU. In most cases D 1 AU, an unphysical result partially due to instrumental effects in the high-energy 3DP detector, but also clearly inconsistent with the assumptions of impulsive and energy-independent injection onsets and scatter-free propagation of the electrons. We also discuss how previous results from cv plot analyses have yielded contradictory andor challenging injection results for the near-relativistic electrons as well as for gradual and impulsive solar energetic ion events.
- Radio Communications