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Published September 1, 1974 | Published
Journal Article Open

The Energy Spectrum of 0.16 to 2 MeV Electrons During Solar Quiet Times


New observations of the quiet-time energy spectrum of 0.16- to 2-MeV electrons have been made with the Caltech Electron/Isotope Spectrometer which was launched on IMP-7 in September 1972. Earlier measurements of quiet-time electrons in this energy range by other groups have resulted in spectra differing by more than an order of magnitude in intensity. A minimum quiet-time flux level somewhat lower than the lowest previously reported spectra and consistent with an extrapolation of the spectrum measured at higher energies is found. A galactic secondary source of knock-on electrons is consistent with these results and with independent studies of the interstellar spectra of cosmic-ray nuclei, provided that solar modulation does not suppress the 0.16- to 2-MeV electron flux by more than a factor of about 3. Although not required, other recently suggested sources may also contribute to the observed fluxes.

Additional Information

© 1974. The American Astronomical Society. Received 1974 February 12. Dr. J. E. Lupton and W. E. Althouse made significant contributions to the design and development of the Electron/Isotope Spectrometer. This work was supported in part by the National Aeronautics and Space Administration under contract NAS5-11066 and grant NGR 05-002-160. One of us (G. J. H.) received support from the National Research Council of Canada while another (E. C. S.) was an Alfred P. Sloan research fellow during this period.

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