Near-Relativistic Electron 1/V Onset Plots

Details Near-Relativistic Electron 1/V Onset Plots Near-Relativistic Electron 1/V Onset Plots

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh31a1146k&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SH31A-1146

Astronomy and Astrophysics

Astronomy

7514 Energetic Particles (2114), 7859 Transport Processes

Scientific paper

It is often assumed that the first arriving electrons of a near-relativistic (E > 30 keV) electron event propagate scatter-free to one Astronomical Unit (AU). In that case, the arrival time, Ta, should scale as D/V, where D is the travel distance and V the electron speed. A plot of Ta versus 1/V for various electron energies should then yield the solar injection time t and the travel distance D. In some electron events D is about 1.2 AU, but the inferred injection times are characteristically about 10 minutes after the start of metric/decametric type III radio bursts that are the assumed signatures of electron injection. This may indicate a delayed injection not directly associated with the type III burst, or it may result from significant coronal/interplanetary electron scattering, even for well beamed events. We use data from the 3DP electron detectors on the Wind spacecraft to do 1/V onset plots for a number of near-relativistic solar electron events. We find that the inferred travel distances are broadly distributed and do not peak at the nominal 1.2 AU value. This may invalidate the scatter-free assumption. If the problem were due to energy independent scattering, the value found for the travel distances should be systematically longer than the nominal value. Most of our values, however, seem to be shorter than the length of the magnetic field lines between the injection point and 1 AU. An energy-dependent scattering with higher scattering at higher energies could make the measured time delays systematically longer at the higher energies and the inferred travel distances systematically shorter. A significant decrease in the efficiency of gyroresonant scattering by whistler mode waves between a few hundred keV and 30 keV might be the cause.

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