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Electron Scattering by High-frequency Whistler Waves at Earth's Bow Shock
Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
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2017 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, no 2, article id L11Article in journal (Refereed) Published
Abstract [en]

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 nonthermal electrons by whistler waves at Earth's bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvn Mach number similar to 11 and a shock angle similar to 84 degrees. 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 Omega(ce), where Omega(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.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2017. Vol. 842, no 2, article id L11
Keywords [en]
acceleration of particles, Earth, shock waves
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-329657DOI: 10.3847/2041-8213/aa7759ISI: 000403671300003OAI: oai:DiVA.org:uu-329657DiVA, id: diva2:1142796
Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2017-09-20Bibliographically approved

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Khotyaintsev, Yuri V.

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Swedish Institute of Space Physics, Uppsala Division
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