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1999 May 09 (M7.6)

A GOES M7.6 solar flare occurred on 1999 May 09 at an H-alpha location of N12W57 (heliographic coordinates). The soft X-ray flux began at 17:53 (64380 s), peaked at 18:07 (65220 s) and ended at 18:15 (65700 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE transient trigger at 64582 s and the four OSSE detectors slewed to the scan-angle position of the Sun and initiated +/- 4.5 degree on-source-off-source viewing strategies.

Significant emission of up to about 400 keV was observed during a ~290 s time interval (64592-64882 s). Count rate time profiles in various energy windows at a temporal resolution of ~8 s are shown in Figure 1. A representative count spectrum is shown in Figure 2. A broken power law which hardened from an index of about -4.9 below a break energy of ~105 keV to about -2.8 above the break energy fit the data better than a single power law. The total fluence above 50 keV was 1981 +/- 10 photons cm-2.

Figure 1

Figure 2

Last revised: 02 Aug 1999