5. Spectrum of flare
We extracted a 2-26 keV spectrum of the complete Sep. 10 flare which amounts to an elapsed time of 5.5 hr and an exposure time of 2.3 hr, and attempted to fit the same Comptonization model as applies to the NFI data when the source is times fainter. Leaving free only the normalizations of the different spectral components, the fit was unsatisfactory with for 24 dof. However, if was allowed to vary, the fit became dramatically better with (23 dof) and cm-2. If instead the black body temperature was allowed to vary, an even better improvement occurred with (23 dof) and k keV. If the Fe-K emission lines at 6.68 and 6.96 keV are replaced for a single one whose energy is left free, the fit improves further to for 23 dof. The line energy then is keV. This suggests a shift of the ionization balance to a lower degree (Fe I-XVII). We determined an average flux over the 3 hr duration of the peak of erg cm-2 s- 1. The equivalent width of the emission line is keV. The flare spectrum is presented in Fig. 7.
© European Southern Observatory (ESO) 2000
Online publication: June 5, 2000