Astron. Astrophys. 360, 729-741 (2000)

Solar energetic particle event and radio bursts associated with the 1996 July 9 flare and coronal mass ejection

T. Laitinen ¹, K.-L. Klein ², L. Kocharov ¹, J. Torsti ¹, G. Trottet ², V. Bothmer ³, M.L. Kaiser ⁴, G. Rank ⁵ and M.J. Reiner <sup>6

1</sup> Space Research Laboratory, Department of Physics, University of Turku, 20014 Turku, Finland
² Observatoire de Paris, Section de Meudon, DASOP & CNRS UMR 8645, 92195 Meudon, France
³ Institut für Experimentelle und Angewandte Physik, Universität Kiel, 24118 Kiel, Germany
⁴ Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁵ Max-Planck-Institute for Extraterrestrial Physics, P.O. Box 1603, 85740 Garching, Germany
⁶ Raytheon ITSS, 4400 Forbes Blvd., Lanham, MD 20706, USA

Received 11 January 2000 / Accepted 11 May 2000

Abstract

Using spaceborne particle and gamma-ray detection and radio diagnostics we study solar energetic particle (SEP) production in the 1996 July 9 event. This event is associated with an impulsive soft X-ray flare (9:10 UT) and a coronal mass ejection (CME). In a global classification the event is considered as mixed-impulsive. A sequence of acceleration processes is identified, starting early in the flare impulsive phase and continuing throughout the period when the CME propagated up to several above the photosphere: (1) Gamma-ray, hard X-ray and cm-wave emitting particles seen during the flare impulsive phase in the low corona had no counterpart at the Solar and Heliospheric Observatory (SoHO) spacecraft. (2) Electrons accelerated at a coronal shock wave were revealed by decimetric-to-metric type  radio emission and by simultaneous radio signatures of beams traveling to 1 AU. (3) Mildly relativistic (250 keV) electrons detected by SoHO did not correspond to these shock-accelerated populations, but to later mainly impulsive injection which was associated with radio brightenings over a large range of coronal altitudes. (4) Energetic protons detected by SoHO were accelerated during about 100 min after the flare impulsive phase with a gradually evolving production profile that bore some similarity with the time profile of broadband metric (type ) emission. (5) While all other particle signatures decayed, a second period of interplanetary proton production took place 2 hours after flare onset. The first, 100 min period of SEP acceleration, post-impulsive phase coronal acceleration, is definitely dominant in mildly relativistic electrons. Two acceleration periods nearly equally contribute to the production of MeV protons. However, the second period is more productive in low energy, MeV, protons.

The timing of the SEP injections indicates that neither the impulsive flare acceleration in the low corona nor the interplanetary CME at are the main sources of the high-energy particles observed onboard SoHO. We suggest that various acceleration processes related to the reconfiguration of the corona in the course of the flare and CME lift-off contribute to the interacting and escaping particle populations, with different signatures at different energies and in different species.

Key words: Sun: corona Sun: flares Sun: particle emission

Send offprint requests to: L. Kocharov (leon.kocharov@srl.utu.fi)

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Contents

• 1. Introduction
• 2. Solar energetic particles
  • 2.1. Gamma-ray observation of the flare impulsive phase
  • 2.2. Overview of the SEP event
  • 2.3. Scenario of electron injection
  • 2.4. Scenario of proton injection
• 3. Radio observations as tracers of coronal electron acceleration
  • 3.1. Spectrographic observations
    • 3.1.1. Microwaves (8 GHz, 3 GHz)
    • 3.1.2. Decimetric to decametric emission (2000-40 MHz)
    • 3.1.3. Hectometer emission (14 MHz)
  • 3.2. Source configuration at decimeter and meter waves
• 4. SEP injection and its relationship with coronal processes
  • 4.1. Impulsive phase acceleration
  • 4.2. Post-impulsive acceleration
    • 4.2.1. Shock acceleration in the middle corona
    • 4.2.2. Acceleration of mildly relativistic interplanetary electrons
    • 4.2.3. Acceleration of interplanetary protons
  • 4.3. Event classification
• 5. Conclusions
• Acknowledgements
• Appendices
  • Appendix A: interplanetary transport model
• References

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000
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