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1991 December 15 (C6.0)

A GOES C6.0 solar flare occurred on 1991 December 15 at an H-alpha location of S12E76 (heliographic coordinates). The soft X-ray flux began at 13:55 (50100 s), peaked at 14:00 (50400 s) and ended at 14:03 (50580 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE transient trigger at 50158 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 emission of up to about 600 keV was observed during a ~180 s time interval (50160-50340 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 -3.8 below a break energy of ~110 keV to about -2.7 above the break energy fit the data better than a single power law. The total fluence above 50 keV was 207.0 +/- 2.0 photons cm-2.

Figure 1

Figure 2

Last revised: 13 Jul 1999