Solar Physics

, 294:22 | Cite as

Onset Time of the GLE 72 Observed at Neutron Monitors and its Relation to Electromagnetic Emissions

  • V. Kurt
  • A. Belov
  • K. Kudela
  • H. MavromichalakiEmail author
  • L. Kashapova
  • B. Yushkov
  • C. Sgouropoulos


We present an overview of the ground-level enhancement (GLE 72) of the cosmic-ray intensity associated with the recent powerful solar flare SOL2017-09-10 (X-ray class X8.9) based on the available neutron monitor (NM) network observations and on data from the satellite GOES 13. The maximum increase at high-latitude near-sea-level NMs was \({\approx }\,6\,\mbox{--}\,7\%\) (2-min averages), greater with better time resolution. A scatter plot of the maximum increase of the GLE versus solar energetic-particle (SEP, proton) flux \({>}\,100~\mbox{MeV}\) shows one of the softest spectra among GLEs relative to the SEP fluxes. However, at two high-mountain middle-latitude NMs the increase was \({\approx }\,1\%\), indicating the possibility of proton acceleration up to 6 GeV. Among the analyzed NM data the Fort Smith (FSMT) NM shows the earliest and the rather high increase between 16:06 – 16:08 UT. This indicates an anisotropy in the first phase of the GLE event. We calculate the acceptance cones of several NM stations at high latitudes and contours of pitch angles corresponding to the interplanetary magnetic field (IMF). When employing the available data we find that pion-decay \(\gamma \)-ray emission onset is in accordance with the time of the main flare energy release. The observed time interval of the impulsive burst of \({>}\,100~\mbox{MeV}\)\(\gamma \)-ray emission probably corresponds to the time of a turbulent current sheet creation. The observed location of the impulsive burst pion-decay emission source coincides with the active region and the cusp-shaped structure. It seems that models assuming sub-relativistic proton production beginning in a turbulent reconnecting current sheet are consistent with the observations. If these particles were released from the Sun during a type III emission with a pion-decay maximum at \(16{:}00{:}30\pm 30~\mbox{UT}\), we get a plausible path length equal to \(1.5\pm 0.3~\mbox{AU}\) of the particles responsible for the onset of the SEP event and GLE. The time lag of GLE 72 corresponds to the most probable interval of the time difference between GLE onset and main flare energy release. Although other scenarios are not excluded we attribute the protons that create the pion-decay emission and the protons responsible for the GLE and SEP event onset to a general population of accelerated particles.


Solar flares, solar energetic particles, cosmic-ray intensity, neutron monitors, ground-level enhancements 



The authors wish to acknowledge the PIs of all neutron monitors ( ), whose data are used in this paper, and GOES data providers. N. Ness of Bartol Institute and CDAWeb are acknowledged for data providing. KK wishes to acknowledge support by the project CRREAT (reg. CZ.02.1.01/0.0/0.0/15003/0000481) call number 02 15 003 of the Operational Program Research, Development and Education. Thanks are due to the anonymous referee for useful comments and suggestions, improving this article. LKK thanks the budgetary funding of the Basic Research program II.16.

Conflict of Interests

The authors declare that there are no conflicts of interest.


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  • V. Kurt
    • 1
  • A. Belov
    • 2
  • K. Kudela
    • 3
    • 4
  • H. Mavromichalaki
    • 5
    Email author
  • L. Kashapova
    • 6
  • B. Yushkov
    • 1
  • C. Sgouropoulos
    • 5
  1. 1.Skobeltsyn Institute of Nuclear PhysicsLomonosov Moscow State UniversityMoscowRussian Federation
  2. 2.IZMIRANTroitskRussian Federation
  3. 3.Nuclear Physics InstituteCzech Academy of SciencesŘežCzech Republic
  4. 4.Institute of Experimental PhysicsSlovak Academy of SciencesKošiceSlovakia
  5. 5.Nuclear and Particle Physics Department, Faculty of PhysicsNational and Kapodistrian University of AthensAthensGreece
  6. 6.Institute of Solar-Terrestrial PhysicsRussian Academy of SciencesIrkutskRussian Federation

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