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1991 November 09 (M1.4)

A GOES M1.4 solar flare occurred on 1991 November 09 at an H-alpha location of S14W69 (heliographic coordinates). The soft X-ray flux began at 20:50 (75000 s), peaked at 20:55 (75300 s) and ended at 21:00 (75600 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE transient trigger at 75106 s and the four OSSE detectors slewed to the scan-angle position of the Sun. Two of the four detectors then initiated +/- 4.5 degree on-source-off-source viewing strategies while the other two detectors remained pointed at the Sun. Because of the extreme DSA-angle of the Sun, however, the views of the top two detectors were obstructed and significant data were recorded by only the bottom two detectors.

Significant emission of up to several MeV was observed during a ~75 s time interval (75120-75195 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 -3.5 below a break energy of ~150 keV to about -2.8 above the break energy fit the data better than a single power law. It appears that a second break is required at about 800 keV to fit the higher energies. The total fluence above 50 keV was 779.6 +/- 9.1 photons cm-2.

Figure 1

Figure 2

Last revised: 27 Jul 1999