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2000 February 04 (M3.0)

A GOES M3.0 solar flare occurred on 2000 February 4 at an H-alpha location of N25E71 (heliographic coordinates). The soft X-ray flux began at 9:11 (33060 s), peaked at 9:19 (33540 s) and ended at 9:28 (34080 s) UT (GOES Geophysical Data Web Site). OSSE received a BATSE transient trigger at 33294 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.

Significant emission to about 200 keV was observed during a ~49 s time interval (33310-33359 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 6.15 +/- 0.08 below a break energy of ~87 keV to 3.21+/- 0.29 above the break energy fit the data better than a single power law. The total fluence above 50 keV and 1 MeV was 29.3 +/- 0.7 and 0.3 +/- 0.9 photons cm-2, respectively. A fit for the 2.223 MeV neutron-capture line showed no significant emission with a 2-sigma upper limit of 0.3 photons cm-2.

The 2.223 MeV line-to->1 MeV fluence ratio varies considerably from flare to flare depending on the flare's accelerated proton-to-electron ratio and location on the Sun (due to limb attenuation of the 2.223 MeV line). For the large flare of 1991 June 4 (located at N30E70) which had a strong nuclear component, this ratio was about 0.3. Based on the measured >1 MeV fluence of the February 4 flare, we would expect a 2.223 MeV line fluence of 0.07 +/- 0.26 photons cm-2 if the flare were similar to the June 4 flare. A measured fluence significantly less than this would imply little or no nuclear emission. The measured upper limit to the line fluence cannot rule out nuclear emission from the January 20 flare.

Figure 1

Figure 2

Last revised: 07 Feb 2000