Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Electron acceleration to relativistic energies at a strong quasi-parallel shock wave

Nature Physics volume 9, pages 164–167 (2013)Cite this article

Subjects

Abstract

Electrons can be accelerated to ultrarelativistic energies at strong (high Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova1,2,3. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock-surface normal (quasi-parallel conditions)4,5,6,7,8. However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn’s bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks4,5,6,7,8. Furthermore, the acceleration led to electrons at relativistic energies (about megaelectronvolt), comparable to the highest energies ever attributed to shock acceleration in the solar wind4. These observations suggest that at high Mach numbers, such as those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on SpringerLink
  • Instant access to the full article PDF.

USD 39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Overview of the spacecraft encounter with Saturn’s bow shock on 3 February 2007.
Figure 2: Observations made during the shock crossing (3 February 2007, 00:00 to 02:00 UT).
Figure 3: Time-averaged electron energy spectra for different intervals during the crossing.
Figure 4: Comparison of LEMMS electron spectra.

Similar content being viewed by others

References

  1. Blandford, R. & Eichler, D. Particle acceleration at astrophysical shocks: A theory of cosmic ray origin. Phys. Rep. 154, 1–75 (1987).

    Article  ADS  Google Scholar 

  2. Aharonian, F. A. et al. High-energy particle acceleration in the shell of a supernova remnant. Nature 432, 75–77 (2004).

    Article  ADS  Google Scholar 

  3. Uchiyama, Y., Aharonian, F. A., Tanaka, T., Takahashi, T. & Maeda, Y. Extremely fast acceleration of cosmic rays in a supernova remnant. Nature 449, 576–578 (2007).

    Article  ADS  Google Scholar 

  4. Sarris, E. T. & Krimigis, S. M. Quasi-perpendicular shock acceleration of ions to ∼ 200 MeV and electrons to ∼ 2 MeV observed by Voyager 2. Astrophys. J. 298, 676–683 (1985).

    Article  ADS  Google Scholar 

  5. Gosling, J. T., Thomsen, M. F., Bame, S. J. & Russell, C. T. Suprathermal electrons at Earth’s bow shock. J. Geophys. Res. 94, 10011–10025 (1989).

    Article  ADS  Google Scholar 

  6. Krimigis, S. M. Voyager energetic particle observations at interplanetary shocks and upstream of planetary bow shocks: 1977–1990. Space Sci. Rev. 59, 167–201 (1992).

    Article  ADS  Google Scholar 

  7. Shimada, N. et al. Diffusive shock acceleration of electrons at an interplanetary shock observed on 21 Feb 1994. Astro. Space Sci. 264, 481–488 (1999).

    Article  ADS  Google Scholar 

  8. Oka, M. et al. Whistler critical Mach number and electron acceleration at the bow shock: Geotail observation. Geophys. Res. Lett. 33, L24104 (2006).

    Article  ADS  Google Scholar 

  9. Treumann, R. A. Fundamentals of collisionless shocks for astrophysical application, 1. Non-relativistic shocks. Astron. Astrophys. Rev. 17, 409–535 (2009).

    Article  ADS  Google Scholar 

  10. Reynolds, S. P. Supernova remnants at high energy. Annu. Rev. Astron. Astrophys. 46, 89–126 (2008).

    Article  ADS  Google Scholar 

  11. Vink, J. Supernova remnants: The X-ray perspective. Astron. Astrophys. Rev. 20, 49–168 (2012).

    Article  ADS  Google Scholar 

  12. Smith, E. J. in Collisionless Shocks in the Heliosphere: Reviews of Current Research (eds Tsurutani, B. T. & Stone, R. G.) 69–83 (Geophysical Monograph Series 35, American Geophysical Union, 1985).

    Book  Google Scholar 

  13. Russell, C. T. in Collisionless Shocks in the Heliosphere: Reviews of Current Research (eds Tsurutani, B. T. & Stone, R. G.) 109–130 (Geophysical Monograph Series 35, American Geophysical Union, 1985).

    Book  Google Scholar 

  14. Levinson, A. Electron injection in collisionless shocks. Astrphys. J. 401, 73–80 (1992).

    Article  ADS  Google Scholar 

  15. Amano, T. & Hoshino, M. A critical Mach number for electron injection in collisionless shocks. Phys. Rev. Lett. 104, 181102 (2010).

    Article  ADS  Google Scholar 

  16. Achilleos, N. et al. Orientation, location, and velocity of Saturn’s bow shock: Initial results from the Cassini spacecraft. J. Geophys. Res. 111, A03201 (2006).

    Article  ADS  Google Scholar 

  17. Went, D. R., Hospodarsky, G. B., Masters, A., Hansen, K. C. & Dougherty, M. K. A new semiempirical model of Saturn’s bow shock based on propagated solar wind parameters. J. Geophys. Res. 116, A07202 (2011).

    ADS  Google Scholar 

  18. Masters, A. et al. Electron heating at Saturn’s bow shock. J. Geophys. Res. 116, A10107 (2011).

    Article  ADS  Google Scholar 

  19. Eastwood, J. P. et al. The foreshock. Space Sci. Rev. 118, 41–94 (2005).

    Article  ADS  Google Scholar 

  20. Burgess, D. et al. Quasi-parallel shock structure and processes. Space Sci. Rev. 118, 205–222 (2005).

    Article  ADS  Google Scholar 

  21. Young, D. T. et al. Cassini plasma spectrometer investigation. Space Sci. Rev. 114, 1–112 (2004).

    Article  ADS  Google Scholar 

  22. Krimigis, S. M. et al. Magnetosphere imaging instrument (MIMI) on the Cassini mission to Saturn/Titan. Space Sci. Rev. 114, 233–329 (2004).

    Article  ADS  Google Scholar 

  23. Krimigis, S. M. et al. Analysis of a sequence of energetic ion and magnetic field events upstream from the Saturnian magnetosphere. Planet. Space Sci. 57, 1785–1794 (2009).

    Article  ADS  Google Scholar 

  24. Dougherty, M. K. et al. The Cassini magnetic field investigation. Space Sci. Rev. 114, 331–383 (2004).

    Article  ADS  Google Scholar 

  25. Gurnett, D. A. et al. The Cassini radio and plasma wave investigation. Space Sci. Rev. 114, 395–463 (2004).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

A.M. acknowledges the support of the JAXA International Top Young Fellowship Program, and P. Gandhi for useful discussions. We thank Cassini instrument Principal Investigators D. A. Gurnett, S. M. Krimigis and D. T. Young. This work was supported by UK STFC through rolling grants to MSSL/UCL and Imperial College London.

Author information

Authors and Affiliations

  1. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa 252-5210, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Japan

    A. Masters, L. Stawarz, M. Fujimoto & H. Hasegawa

  2. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan

    M. Fujimoto

  3. Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, London SW7 2AZ, Prince Consort Road, UK

    S. J. Schwartz & M. K. Dougherty

  4. Office of Space Research and Technology, Academy of Athens, Soranou Efesiou 4, 11527 Athens, Greece

    N. Sergis

  5. Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

    M. F. Thomsen

  6. Laboratoire de Physique des Plasmas, Centre National de la Recherche Scientifique, Observatoire de Saint-Maur, 4 avenue de Neptune, Saint-Maur-Des-Fossés 94107, France

    A. Retinò & P. Canu

  7. Center for Space Physics, Boston University, Massachusetts 02215, 725 Commonwealth Avenue, Boston, USA

    B. Zieger

  8. Department of Space and Climate Physics, Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT, UK

    G. R. Lewis & A. J. Coates

  9. The Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, UK

    G. R. Lewis & A. J. Coates

Authors
  1. A. Masters
    View author publications

    Search author on:PubMed Google Scholar

  2. L. Stawarz
    View author publications

    Search author on:PubMed Google Scholar

  3. M. Fujimoto
    View author publications

    Search author on:PubMed Google Scholar

  4. S. J. Schwartz
    View author publications

    Search author on:PubMed Google Scholar

  5. N. Sergis
    View author publications

    Search author on:PubMed Google Scholar

  6. M. F. Thomsen
    View author publications

    Search author on:PubMed Google Scholar

  7. A. Retinò
    View author publications

    Search author on:PubMed Google Scholar

  8. H. Hasegawa
    View author publications

    Search author on:PubMed Google Scholar

  9. B. Zieger
    View author publications

    Search author on:PubMed Google Scholar

  10. G. R. Lewis
    View author publications

    Search author on:PubMed Google Scholar

  11. A. J. Coates
    View author publications

    Search author on:PubMed Google Scholar

  12. P. Canu
    View author publications

    Search author on:PubMed Google Scholar

  13. M. K. Dougherty
    View author publications

    Search author on:PubMed Google Scholar

Contributions

A.M. identified the event, analysed the combined data set, proposed the interpretation and wrote the paper. L.S., M.F., S.J.S., H.H. and B.Z. discussed the interpretation. N.S., M.F.T., A.R. and G.R.L. each analysed, and checked the interpretation of, one data set. A.J.C., P.C. and M.K.D. oversaw the data analysis and interpretation. All authors reviewed the manuscript.

Corresponding author

Correspondence to A. Masters.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Masters, A., Stawarz, L., Fujimoto, M. et al. Electron acceleration to relativistic energies at a strong quasi-parallel shock wave. Nature Phys 9, 164–167 (2013). https://doi.org/10.1038/nphys2541

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue date:

  • DOI: https://doi.org/10.1038/nphys2541

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing