skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: SUPRATHERMAL ELECTRONS AT SATURN'S BOW SHOCK

Abstract

The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini . The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, <28 keV) during shock crossings, but the higher energy channels were at (or close to) background. The high-energy electron detector (MIMI-LEMMS, >18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (<100 keV) were above background. We show that these results are consistent with the theory in which the “injection” of thermal electrons into an accelerationmore » process involves interaction with whistler waves at the shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong shocks around young SNRs. A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ∼1 MeV).« less

Authors:
;  [1];  [2];  [3];  [4];  [5]
  1. The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom)
  2. Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)
  3. Office of Space Research and Technology, Academy of Athens, Soranou Efesiou 4, 11527 Athens (Greece)
  4. Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow (Poland)
  5. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
Publication Date:
OSTI Identifier:
22665997
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 826; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; ASTROPHYSICS; COLLISIONLESS PLASMA; COSMIC RADIATION; DATA ANALYSIS; DISTRIBUTION; ELECTRONS; GALAXIES; INTERACTIONS; KEV RANGE; MACH NUMBER; MAGNETIC FIELDS; MEV RANGE; RELATIVISTIC RANGE; SATURN PLANET; SHOCK WAVES; SOLAR WIND; SPACE VEHICLES; SUPERNOVA REMNANTS; TAIL ELECTRONS

Citation Formats

Masters, A., Dougherty, M. K., Sulaiman, A. H., Sergis, N., Stawarz, L., Fujimoto, M., and Coates, A. J., E-mail: a.masters@imperial.ac.uk. SUPRATHERMAL ELECTRONS AT SATURN'S BOW SHOCK. United States: N. p., 2016. Web. doi:10.3847/0004-637X/826/1/48.
Masters, A., Dougherty, M. K., Sulaiman, A. H., Sergis, N., Stawarz, L., Fujimoto, M., & Coates, A. J., E-mail: a.masters@imperial.ac.uk. SUPRATHERMAL ELECTRONS AT SATURN'S BOW SHOCK. United States. https://doi.org/10.3847/0004-637X/826/1/48
Masters, A., Dougherty, M. K., Sulaiman, A. H., Sergis, N., Stawarz, L., Fujimoto, M., and Coates, A. J., E-mail: a.masters@imperial.ac.uk. 2016. "SUPRATHERMAL ELECTRONS AT SATURN'S BOW SHOCK". United States. https://doi.org/10.3847/0004-637X/826/1/48.
@article{osti_22665997,
title = {SUPRATHERMAL ELECTRONS AT SATURN'S BOW SHOCK},
author = {Masters, A. and Dougherty, M. K. and Sulaiman, A. H. and Sergis, N. and Stawarz, L. and Fujimoto, M. and Coates, A. J., E-mail: a.masters@imperial.ac.uk},
abstractNote = {The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini . The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, <28 keV) during shock crossings, but the higher energy channels were at (or close to) background. The high-energy electron detector (MIMI-LEMMS, >18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (<100 keV) were above background. We show that these results are consistent with the theory in which the “injection” of thermal electrons into an acceleration process involves interaction with whistler waves at the shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong shocks around young SNRs. A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ∼1 MeV).},
doi = {10.3847/0004-637X/826/1/48},
url = {https://www.osti.gov/biblio/22665997}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 826,
place = {United States},
year = {Wed Jul 20 00:00:00 EDT 2016},
month = {Wed Jul 20 00:00:00 EDT 2016}
}