34th Solar Physics Division Meeting, June 2003
Session 22 RHESSI Results III
Oral, Thursday, June 19, 2003, 9:00-10:30am, Auditorium

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[22.02] Why was there no Solar Energetic Particle Event Associated with the Gamma-ray-line Flare of 2002 July 23?

N Gopalswamy, B. R. Dennis, M. L. Kaiser (NASA/GSFC), S. Krucker, R. P. Lin (Berkeley), A. Vourlidas (NRL)

We investigated the coronal and interplanetary (IP) events associated with two X-class flares on 2002 July 20 and 23. Both flares were associated with ultra-fast (>2000 km~s-1) coronal mass ejections (CMEs) and IP shocks. We use white-light, EUV, hard X-ray and radio observations to trace the origin of the CMEs to active region 0039 located close to the east limb. The July 20 flare was partly occulted by the east limb, yet it resulted in a major solar energetic particle event with intensity ~ 20 pfu in the >10 MeV channel (1 pfu = 1 particle per (cm2 s sr MeV)). The July 23 event was the first gamma-ray-line flare detected by RHESSI, but it did not show any enhancement in SEPs above the elevated background from the July 20 event. We identified two distinguishing factors between the July 2 and July 23 CMEs: (1) The July 20 CME had a higher kinetic energy, and (2) The July 20 CME was interacting with another fast CME (1350 km~s-1) that preceded by less than an hour from the same region; there were also two other CMEs on July 19 from the same region. Thus the coronal and IP environment of the July 20 event was highly disturbed due to preceding CMEs (as compared to the July 23 event). We suggest that the different coronal/IP environments may be responsible for the lack of SEP event associated with the July 23 event.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.