Electron Scattering by High-frequency Whistler Waves at Earth’s Bow Shock

Journal Article · Tue Jun 20 04:00:00 EDT 2017 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8213/AA7759· OSTI ID:22872622

Oka, M.; Phan, T. D.; Hull, A. J.; Agapitov, O. ^[1]; III, L. B. Wilson; Gershman, D. J.; Dorelli, J. C.; Giles, B. L.; Moore, T. E.; Avanov, L. A.; Paterson, W. ^[2]; Amano, T.; Hoshino, M. ^[3]; Argall, M. R.; Torbert, R. B. ^[4]; Contel, O. Le ^[5]; Khotyaintsev, Y. V. ^[6]; Burch, J. L. ^[7]; Pollock, C. ^[8]; others, and

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1. Space Sciences Laboratory, University of California Berkeley, Berkeley, CA 94720-7450 (United States)
2. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
3. Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)
4. Physics Department and Space Science Center, University of New Hampshire, Durham, NH (United States)
5. Laboratoire de Physique des Plasmas (LPP—UMR 7648), CNRS/Ecole Polytechnique/UPMC/Univ. Paris-Sud/Obs. de Paris, Universit Pierre et Marie Curie, place Jussieu, F-75252 Paris Cedex 05 (France)
6. Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala (Sweden)
7. Southwest Research Institute, San Antonio, TX 78228 (United States)
8. Denali Scientific, Healy, AK 99743 (United States)

Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth’s bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ∼11 and a shock angle ∼84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5–2 keV) electron flux, correlated with high-frequency (0.2–0.4 Ω{sub ce}, where Ω{sub ce} is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

• OSTI ID: 22872622
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 842; ISSN 2041-8205
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ALFVEN WAVES
ASTROPHYSICS
CYCLOTRON FREQUENCY
CYCLOTRON RESONANCE
EARTH MAGNETOSPHERE
EARTH PLANET
ELECTRONS
FREQUENCY RANGE
KEV RANGE
MACH NUMBER
MAGNETIC FIELDS
PHASE SPACE
PLASMA
SCATTERING
SHOCK WAVES
WHISTLERS