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1999 August 28 (M2.8)

A GOES M2.8 solar flare occurred on 1999 August 28 at an H-alpha location of S26W16 (heliographic coordinates). The soft X-ray flux began at 00:50 (3000 s), peaked at 1:02 (3720 s), and ended at 1:16 (4560 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE solar-flare trigger at 11418 s and the OSSE detectors slewed to the scan-angle position of the Sun. Two OSSE detectors were aimed directly at the sun while the other two initiated standard on-source-off-source viewing strategies. Solar observations began at 3300 s UT.

Significant gamma-ray emission to ~200 keV was observed lasting until about 3440 s UT with one peak of emmision at ~3400 s. Count rate time profiles in various energy windows at a temporal resolution of ~8 s are shown in Figure 1. Figure 2 shows a representative count spectrum obtained from one Sun-pointed detector integrated over the time period 3362-3444 s UT (82 seconds). The electron bremsstrahlung component was well-fit with a simple power law having a spectral index of ~4.06. There was no evidence for nuclear lines.

Figure 1

Figure 2

Last revised: 11 Dec 1997