Statistical analysis of suprathermal electron drivers at 67P/Churyumov–Gerasimenko

Broiles, Thomas W.; Burch, J. L.; Chae, K.; Clark, G.; Cravens, T. E.; Eriksson, A.; Fuselier, S. A.; Frahm, R. A.; Gasc, Sébastien; Goldstein, R.; Henri, P.; Koenders, C.; Livadiotis, G.; Mandt, K. E.; Mokashi, P.; Nemeth, Z.; Odelstad, E.; Rubin, Martin; Samara, M. (2016). Statistical analysis of suprathermal electron drivers at 67P/Churyumov–Gerasimenko. Monthly notices of the Royal Astronomical Society, 462(Suppl1), S312-S322. Oxford University Press 10.1093/mnras/stw2942

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We use observations from the Ion and Electron Sensor (IES) on board the Rosetta spacecraft to study the relationship between the cometary suprathermal electrons and the drivers that affect their density and temperature. We fit the IES electron observations with the summation of two kappa distributions, which we characterize as a dense and warm population (∼10 cm−3 and ∼16 eV) and a rarefied and hot population (∼0.01 cm−3 and ∼43 eV). The Parameters of our fitting technique determine the populations’ density, temperature, and invariant kappa index. We focus our analysis on the warm population to determine its origin by comparing the density and temperature with the neutral density and magnetic field strength. We find that the warm electron population is actually two separate sub-populations: electron distributions with temperatures above 8.6 eV and electron distributions with temperatures below 8.6 eV. The two sub-populations have different relationships between their density and temperature. Moreover, the two sub-populations are affected by different drivers. The hotter sub-Population temperature is strongly correlated with neutral density, while the cooler sub-population is unaffected by neutral density and is only weakly correlated with magnetic field strength. We suggest that the population with temperatures above 8.6 eV is being heated by lower hybrid waves driven by counterstreaming solar wind protons and newly formed, cometary ions created in localized, dense neutral streams. To the best of our knowledge, this represents the first observations of cometary electrons heated through wave–particle interactions.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Gasc, Sébastien and Rubin, Martin

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

0035-8711

Publisher:

Oxford University Press

Language:

English

Submitter:

Katharina Weyeneth-Moser

Date Deposited:

19 Jul 2017 08:10

Last Modified:

19 Jul 2017 08:10

Publisher DOI:

10.1093/mnras/stw2942

BORIS DOI:

10.7892/boris.97004

URI:

https://boris.unibe.ch/id/eprint/97004

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