Solar Physics

, Volume 291, Issue 11, pp 3385–3426 | Cite as

Spatio-temporal Dynamics of Sources of Hard X-Ray Pulsations in Solar Flares

  • S. A. Kuznetsov
  • I. V. Zimovets
  • A. S. Morgachev
  • A. B. Struminsky
Waves in the Solar Corona


We present a systematic analysis of the spatio-temporal evolution of sources of hard X-ray (HXR) pulsations in solar flares. We concentrate on disk flares whose impulsive phases are accompanied by a series of more than three successive peaks (pulsations) of HXR emission detected in the RHESSI 50 – 100 keV energy channel with a four-second time cadence. Twenty-nine such flares observed from February 2002 to June 2015 with characteristic time differences between successive peaks \(P \approx8\,\mbox{--}\,270~\mbox{s}\) are studied. The main observational result of the analysis is that sources of HXR pulsations in all flares are not stationary, they demonstrate apparent movements or displacements in the parent active regions from pulsation to pulsation. The flares can be subdivided into two main groups depending on the character of the dynamics of the HXR sources. Group 1 consists of 16 flares (\(55~\%\)) that show systematic dynamics of the HXR sources from pulsation to pulsation with respect to a magnetic polarity inversion line (MPIL), which has a simple extended trace on the photosphere. Group 2 consists of 13 flares (\(45~\%\)) that show more chaotic displacements of the HXR sources with respect to an MPIL with a more complex structure, and sometimes several MPILs are present in the parent active regions of such flares. Based on the observations, we conclude that the mechanism of the flare HXR pulsations (at least with time differences of the considered range) is related to successive triggering of the flare energy release process in different magnetic loops (or bundles of loops) of the parent active regions. Group 1 flare regions consist of loops stacked into magnetic arcades that are extended along MPILs. Group 2 flare regions have more complex magnetic structures, and the loops are arranged more chaotically and randomly there. We also found that at least 14 (\(88~\%\)) group 1 flares and 11 (\(85~\%\)) group 2 flares are accompanied by coronal mass ejections (CMEs), i.e. the absolute majority of the flares we studied are eruptive events. This gives a strong indication that eruptive processes play an important role in the generation of HXR pulsations in flares. We suggest that an erupting flux rope can act as a trigger of the flare energy release. Its successive interaction with different loops of a parent active region can lead to apparent motion of HXR sources and to a series of HXR pulsations. However, the exact mechanism responsible for generating the pulsations remains unclear and requires a more detailed investigation.


Flares, dynamics Flares, impulsive phase Flares, relation to magnetic field X-Ray bursts, hard 



We thank V.M. Nakariakov, V.F. Melnikov, S.A. Anfinogentov, E.P. Kontar for helpful discussions, E.G. Kupriyanova for help with the wavelet analysis, A.R. Inglis for help with the English. We would like to acknowledge the anonymous referee for useful comments that helped to improve the manuscript. We are grateful to the spacecraft teams and consortia (RHESSI, SOHO/MDI, SOHO/LASCO, SDO/HMI, GOES) and ground-based observatories (RSTN, e-Callisto) whose data were used in this study. This study was supported by the Russian Foundation for Basic Research (grants No. 16-02-00328, 16-32-00535, 15-32-50998, 15-32-21078, 14-02-00924) and by the Marie Curie FP7 PIRSES-GA-2011-295272 “RadioSun” Project. We are also grateful to the Specialized Research Fund for State Key Laboratories of China.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  • S. A. Kuznetsov
    • 1
    • 2
    • 3
  • I. V. Zimovets
    • 2
    • 3
    • 4
    • 5
  • A. S. Morgachev
    • 1
    • 2
  • A. B. Struminsky
    • 3
    • 6
  1. 1.Radiophysical Research Institute (NIRFI)Nizhny NovgorodRussia
  2. 2.Central Astronomical Observatory at Pulkovo of the Russian Academy of SciencesSaint-PetersburgRussia
  3. 3.Space Research Institute (IKI) of the Russian Academy of SciencesMoscowRussia
  4. 4.State Key Laboratory of Space Weather (SKSW)National Space Science Center (NSSC) of the Chinese Academy of SciencesBeijingChina
  5. 5.International Space Science Institute – Beijing (ISSI-BJ)BeijingChina
  6. 6.Moscow Institute of Physics and Technology (State University)DolgoprudnyRussia

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