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1998 May 29 (M6.7)

A GOES M6.7 solar flare occurred on 1998 May 29 at an H-alpha location of N20E81 (heliographic coordinates). The soft X-ray flux began at 00:51 (3060 s), peaked at 00:59 (3540 s), and ended at 01:03 (3780 s) UT (GOES Geophysical Data Web Site). The Sun was an OSSE target during this period and two of the four detectors were observing the Sun when the flare occurred.

Significant emission up to several MeV was observed for ~100 s (3338 - 3437 s UT). Count rate time profiles in various energy windows at a temporal resolution of ~16 s are shown in Figure 1. A representative count spectrum is shown in Figure 2. The total fluence above 50 keV was 916 +/- 15 photons cm-2. (This should be considered a lower limit because we have not accounted for possible additional dead-time due to high counting rates.) There was no evidence for nuclear line emission suggesting that this flare was electron rich. A broken power law with a break energy at ~160 keV provided a better fit to the data than a single power law. Such a spectral break in the electron bremsstrahlung spectrum has been observed in other flares but this is the first time that the energy range around the break energy has been measured with a single detector.

Figure 1

Figure 2

Last revised: 11 Dec 1997