Electron injection by whistler waves in non-relativistic shocks

Mario A. Riquelme, Anatoly Spitkovsky

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Radio and X-ray observations of shocks in young supernova remnants (SNRs) reveal electron acceleration to non-thermal, ultra-relativistic energies (~ 10-100 TeV). This acceleration is usually assumed to happen via the diffusive shock acceleration (DSA) mechanism. However, the way in which electrons are initially energized or 'injected' into this acceleration process is an open question and the main focus of this work. We present our study of electron acceleration in nonrelativistic shocks using 2D and 3D particle-in-cell (PIC) plasma simulations. Our simulations show that significant non-thermal acceleration happens due to the growth of oblique whistler waves in the foot of quasi-perpendicular shocks. The obtained electron energy distributions show power law tails with spectral indices up to α ~ 3-4. Also, the maximum energies of the accelerated particles are consistent with the electron Larmor radii being comparable to that of the ions, indicating potential injection into the subsequent DSA process. This injection mechanism requires the shock waves to have fairly low Alfvénic Mach numbers, MA <20, which is consistent with the theoretical conditions for the growth of whistler waves in the shock foot (MA <(mi/me)1/2). Thus, if this mechanism is the only robust electron injection process at work in SNR shocks, then SNRs that display non-thermal emission must have significantly amplified upstream magnetic fields. Such field amplification is likely achieved by accelerated ions in these environments, so electron and ion acceleration in SNR shocks must be interconnected.

Original languageEnglish (US)
Title of host publicationWaves and Instabilities in Space and Astrophysical Plasmas
Pages182-193
Number of pages12
DOIs
StatePublished - Dec 1 2012
EventWorkshop on Waves and Instabilities in Space and Astrophysical Plasmas - Eilat, Israel
Duration: Jun 19 2011Jun 24 2011

Publication series

NameAIP Conference Proceedings
Volume1439
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Other

OtherWorkshop on Waves and Instabilities in Space and Astrophysical Plasmas
CountryIsrael
CityEilat
Period6/19/116/24/11

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Keywords

  • Acceleration of particles
  • Cosmic rays
  • Plasmas
  • Shock waves

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  • Cite this

    Riquelme, M. A., & Spitkovsky, A. (2012). Electron injection by whistler waves in non-relativistic shocks. In Waves and Instabilities in Space and Astrophysical Plasmas (pp. 182-193). (AIP Conference Proceedings; Vol. 1439). https://doi.org/10.1063/1.3701360