Back To OSSE Solar Flare Web Page


Get Ghostscript

1991 October 24 (X2.1)

A GOES X2.1 solar flare occurred on 1991 October 24 at an H-alpha location of S14E59 (heliographic coordinates). The soft X-ray flux began at 02:31 (9060 s), peaked at 02:40 {9600 s) and ended at 02:56 (10560 s) UT (GOES Geophysical Data Web Site). At the time of the flare, OSSE was observing CenA with all four detectors performing +/- 4.5 degree on-source-off-source viewing strategies. A BATSE trigger was received at 9420 s UT but the event was not identified as solar so OSSE continued to observe CenA. As a result, the Sun was located about 32 degrees off-axis.

Significant emmission of up to at least 10 MeV was observed during an ~65 s time interval (9456-9521 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 single power law did not provide an adequate fit to the data. The data were better fit with a power law and a nuclear line model. The best-fit power law had an index of 2.42 +/- 0.31 and a fluence above 1 MeV of 19.0 +/- 5.7 photons cm-2. The total fluence in the 2.223 MeV neutron-capture line was 7.3 +/- 1.0 photons cm-2 and in narrow nuclear lines above 1 MeV was 5.7 +/- 1.2 photons cm-2.

Figure 1

Figure 2

Last revised: 11 Dec 1997