Journal article
Plasma line detected by Voyager 1 in the interstellar medium: Tips and traps for quasi-thermal noise spectroscopy
Astronomy and astrophysics (Berlin), Vol.679, A146
11/2023
DOI: 10.1051/0004-6361/202347455
Abstract
The quasi-thermal motion of plasma particles produces electrostatic fluctuations, whose voltage power spectrum induced on electric
antennas reveals plasma properties. In weakly magnetised plasmas, the main feature of the spectrum is a line at the plasma frequency –
proportional to the square root of the electron density – whose global shape can reveal the electron temperature, while the fine structure
reveals the suprathermal electrons. Since it is based on electrostatic waves, quasi-thermal noise spectroscopy (QTN) provides in situ
measurements. This method has been successfully used for more than four decades in a large variety of heliosphere environments.
Very recently, it has been tentatively applied in the very local interstellar medium (VLISM) to interpret the weak line discovered on
board Voyager 1 and in the context of the proposed interstellar probe mission. The present paper shows that the line is still observed
in the Voyager Plasma Wave Science data, and concentrates on the main features that distinguish the plasma QTN in the VLISM
from that in the heliosphere. We give several tools to interpret it in this medium and highlight the errors arising when it is interpreted
without caution, as has recently been done in several publications. We show recent solar wind data, which confirm that the electric
field of the QTN line in a weakly magnetised stable plasma is not aligned with the local magnetic field. We explain why the amplitude
of the line does not depend on the concentration of suprathermal electrons, and why its observation with a short antenna does not
require a kappa electron velocity distribution. Finally, we suggest an origin for the suprathermal electrons producing the QTN and
we summarise the properties of the VLISM that could be deduced from an appropriate implementation of QTN spectroscopy on a
suitably designed instrument.
Details
- Title: Subtitle
- Plasma line detected by Voyager 1 in the interstellar medium: Tips and traps for quasi-thermal noise spectroscopy
- Creators
- N. Meyer-VernetA. LecacheuxM. MoncuquetK. IssautierW. S. Kurth
- Resource Type
- Journal article
- Publication Details
- Astronomy and astrophysics (Berlin), Vol.679, A146
- DOI
- 10.1051/0004-6361/202347455
- ISSN
- 0004-6361
- eISSN
- 1432-0746
- Language
- English
- Electronic publication date
- 10/12/2023
- Date published
- 11/2023
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984479182202771
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