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1991 December 26 (M4.6)

A GOES M4.6 solar flare occurred on 1991 December 26. 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 10:47 (38820 s), peaked at 10:50 (39000 s) and ended at 10:54 (39240 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE transient trigger at 38857 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 300 keV was observed during a ~150 s time interval (38865-39015 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 single power law with an index of about -3.8 was used to fit the data. The total fluence above 50 keV was 843 +/- 13 photons cm-2.

Figure 1

Figure 2

Last revised: 13 Jul 1999