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Hard X-ray emission from the solar corona

  • Review Article
  • Published:
The Astronomy and Astrophysics Review Aims and scope

Abstract

This review surveys hard X-ray emissions of non-thermal electrons in the solar corona. These electrons originate in flares and flare-related processes. Hard X-ray emission is the most direct diagnostic of electron presence in the corona, and such observations provide quantitative determinations of the total energy in the non-thermal electrons. The most intense flare emissions are generally observed from the chromosphere at footpoints of magnetic loops. Over the years, however, many observations of hard X-ray and even γ-ray emission directly from the corona have also been reported. These coronal sources are of particular interest as they occur closest to where the electron acceleration is thought to occur. Prior to the actual direct imaging observations, disk occultation was usually required to study coronal sources, resulting in limited physical information. Now RHESSI has given us a systematic view of coronal sources that combines high spatial and spectral resolution with broad energy coverage and high sensitivity. Despite the low density and hence low bremsstrahlung efficiency of the corona, we now detect coronal hard X-ray emissions from sources in all phases of solar flares. Because the physical conditions in such sources may differ substantially from those of the usual “footpoint” emission regions, we take the opportunity to revisit the physics of hard X-radiation and relevant theories of particle acceleration.

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Authors and Affiliations

  1. Space Sciences Laboratory, University of California, Berkeley, CA, 94720-7450, USA

    S. Krucker & H. S. Hudson

  2. Institute of Astronomy, ETH Zurich, 8093, Zurich, Switzerland

    M. Battaglia

  3. Space and Atmospheric Physics, Blackett Laboratory, Imperial College, London, SW7 2BW, UK

    P. J. Cargill

  4. Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK

    L. Fletcher

  5. DACE/Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK

    A. L. MacKinnon

  6. Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 4648601, Japan

    S. Masuda

  7. NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD, 20771, USA

    L. Sui

  8. Astronomical Institute, University of Wroclaw, ul. Kopernika 11, 51-622, Wroclaw, Poland

    M. Tomczak

  9. Institute of Physics/IGAM, University of Graz, Universitätsplatz 5, 8010, Graz, Austria

    A. L. Veronig

  10. Department of Physics, University of Thessaloniki, Thessaloniki, 54124, Greece

    L. Vlahos

  11. Astronomy Department, University of Maryland, College Park, MD, 20742, USA

    S. M. White

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The Reuven Ramaty High-Energy Solar Spectroscopic Imager; see Lin et al. (2002).

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Krucker, S., Battaglia, M., Cargill, P.J. et al. Hard X-ray emission from the solar corona. Astron Astrophys Rev 16, 155–208 (2008). https://doi.org/10.1007/s00159-008-0014-9

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