The Astronomy and Astrophysics Review

, Volume 16, Issue 3–4, pp 155–208 | Cite as

Hard X-ray emission from the solar corona

  • S. Krucker
  • M. Battaglia
  • P. J. Cargill
  • L. Fletcher
  • H. S. Hudson
  • A. L. MacKinnon
  • S. Masuda
  • L. Sui
  • M. Tomczak
  • A. L. Veronig
  • L. Vlahos
  • S. M. White
Review Article


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.


Sun Corona Hard X-rays 


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • S. Krucker
    • 1
  • M. Battaglia
    • 2
  • P. J. Cargill
    • 3
  • L. Fletcher
    • 4
  • H. S. Hudson
    • 1
  • A. L. MacKinnon
    • 5
  • S. Masuda
    • 6
  • L. Sui
    • 7
  • M. Tomczak
    • 8
  • A. L. Veronig
    • 9
  • L. Vlahos
    • 10
  • S. M. White
    • 11
  1. 1.Space Sciences LaboratoryUniversity of CaliforniaBerkeleyUSA
  2. 2.Institute of AstronomyETH ZurichZurichSwitzerland
  3. 3.Space and Atmospheric PhysicsBlackett Laboratory, Imperial CollegeLondonUK
  4. 4.Department of Physics and AstronomyUniversity of GlasgowGlasgowUK
  5. 5.DACE/Department of Physics and AstronomyUniversity of GlasgowGlasgowUK
  6. 6.Solar-Terrestrial Environment LaboratoryNagoya UniversityNagoyaJapan
  7. 7.NASA Goddard Space Flight CenterSolar Physics LaboratoryGreenbeltUSA
  8. 8.Astronomical InstituteUniversity of WroclawWroclawPoland
  9. 9.Institute of Physics/IGAMUniversity of GrazGrazAustria
  10. 10.Department of PhysicsUniversity of ThessalonikiThessalonikiGreece
  11. 11.Astronomy DepartmentUniversity of MarylandCollege ParkUSA

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