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

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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 6

1 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


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 [FORMULA] 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 [FORMULA] radio emission and by simultaneous radio signatures of beams traveling to 1 AU. (3) Mildly relativistic ([FORMULA]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 [FORMULA]) emission. (5) While all other particle signatures decayed, a second period of interplanetary proton production took place [FORMULA]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 [FORMULA] MeV protons. However, the second period is more productive in low energy, [FORMULA] MeV, protons.

The timing of the SEP injections indicates that neither the impulsive flare acceleration in the low corona nor the interplanetary CME at [FORMULA] 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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© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000