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An interpretation of a mysterious 3.0- to 4.6-kHz emission band observed on Voyager 2 near NeptuneA whistler mode interpretation is provided for the narrowband signal (f approx. 3 - 4.6 kHz, Delta f approx. 200 - 800 Hz) detected by the plasma wave instrument on Voyager 2 during its encounter with Neptune. Our analysis indicates that this signal may have been generated in a limited spatial region and that it propagated to other regions of the Neptunian magnetosphere in the nonducted whistler mode with wave normal vectors lying close to the whistler mode resonance cone. The observed frequency variation of the emission along the Voyager 2 trajectory is consistent with this interpretation. The source location is estimated to be near the magnetic equator at L approx. 4 and dipole longitude of 111 deg W (260 deg W longitude in Neptune coordinate system). The source frequency and bandwidth are estimated to be 3.6 kHz and 300 Hz, respectively. The waves most likely would have been generated by energetic electrons with 2- to 20-keV parallel energy via a gyroresonance mechanism. Our interpretation of the narrowband emissions places the following limits on the Neptunian thermal plasma density and temperature: (1) N(sub e, min) greater than 0.16 el/cu cm for 1.2 R(sub N) less than R less than 5 R(sub N), (2) N(sub e, max) = 597.5/cu cm at R - 1.3 R(sub N), (3) T(sub e, max) less than 500-1000 K at R approx. 5 R(sub N). It is also possible that the weak UV aurora observed near Neptune could have been caused by the precipitation of energetic particles by the narrowband emission as a result of wave particle interactions.
Document ID
19950046217
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Sonwalkar, Vikas S.
(Stanford Univ. Stanford, CA, United States)
Inan, Umran S.
(Stanford Univ. Stanford, CA, United States)
Bell, Timothy F.
(Stanford Univ. Stanford, CA, United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: A2
ISSN: 0148-0227
Subject Category
Astrophysics
Accession Number
95A77816
Funding Number(s)
CONTRACT_GRANT: NAGW-2894
Distribution Limits
Public
Copyright
Other

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