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1991 December 27 (M1.3)

A GOES M1.3 solar flare occurred on 1991 December 27. The location of the flare on the Solar surface is not known due to lack of an accompanying H-alpha event. The soft X-ray flux began at 11:06 (39960 s), peaked at 11:13 (40380 s) and ended at 11:22 (40920 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE transient trigger at 40007 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 bulk of the flare, and significant data were recorded by this detector.

Significant emission of up to about 200 keV was observed during a ~130 s time interval (40065-40195 s). 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. A broken power law which hardened from an index of about -5.2 below a break energy of ~145 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 524.9 +/- 9.3 photons cm-2.

Figure 1

Figure 2

Last revised: 13 Jul 1999