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1991 December 16 (C7.5)

A GOES C7.5 solar flare occurred on 1991 December 16 at an H-alpha location of N09W01 (heliographic coordinates). The soft X-ray flux began at 00:44 (2640 s), peaked at 01:03 (3780 s) and ended at 01:07 (4020 s) UT (GOES Geophysical Data Website). OSSE received a BATSE transient trigger at 3550 s but did not respond because the four OSSE detectors were involved in a complicated chopping procedure to observe the Galactic center. Fortunately, one of the detectors happened to be pointed at the scan-angle position of the Sun for the duration of the flare, and significant data were recorded by this detector.

Significant emmission of up to about 200 keV was observed during a ~60 s time interval (3685-3745 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 steepened from an index of about -3.7 below a break energy of ~95 keV to about -5.0 above the break energy fit the data better than a single power law. The total fluence above 50 keV was 119.2 +/- 2.5 photons cm-2.

Figure 1

Figure 2

Last revised: 15 Jul 1999