Astron. Astrophys. 357, 520-526 (2000)

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.

Fig. 7. Spectrum of the second flare and the fit with the Comptonized model with black body component of temperature k keV and an emission line at 6.4 keV. The lower panel presents the residuals in units of sigma per channel.

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000
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