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1997 November 27 (X2.6)

A GOES X2.6 solar flare occurred on 1997 November 27 at an H-alpha location of N17E63 (heliographic coordinates). The soft X-ray flux began at 12:59 (46740 s), peaked at 13:17 (47820 s), and ended at 13:20 (48000 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE solar-flare trigger at 47595 s and the four OSSE detectors slewed to the scan-angle position of the Sun and initiated +/- 4.5 degree on-source-off-source viewing strategies. The Sun was rapidly acquired because it was already within the region of sky covered by the current OSSE observations.

Significant emission up to several MeV was observed during the subsequent three ~131-second data accumulation intervals (47617-47748, 47748-47879, 47879-48010 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 obtained during the second interval is shown in Figure 2. Electron bremsstrahlung and narrow nuclear lines at 0.51, 1.0, 1.6, 2.223, 4.4, 6.1 MeV can be seen. Fits to the data show that the electron bremsstrahlung began during the first interval and peaked during the second interval. The spectrum of this bremsstrahlung hardened with time, from a power law index of ~4.4 to ~3.4. Significant nuclear line emission was measured only during the second interval and the delayed 2.223 MeV neutron-capture line continued into the third interval. The total fluences of these components are given in the table. (These fluences should be considered lower limits because there my be additional dead-time due to high counting rates that we have not accounted for.) The ratios of the narrow nuclear lines and the 2.223 MeV line to the >300 keV bremsstrahlung are consistent with the ratios determined for flares observed with SMM (e.g., see Murphy et al. 1993). The nuclear line and 2.223 MeV line fluences observed from this flare are less than any measured for the SMM flares.

Emission component
(photons cm-2)
Narrow nuclear lines
1.2 +/- 0.6
2.223 MeV neutron capture
1.2 +/- 0.3
>300 keV bremsstrahlung
25.2 +/- 4.1
>50 keV bremsstrahlung
680 +/- 34

Figure 1

Figure 2

Last revised: 11 Dec 1997