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Astron. Astrophys. 340, L19-L22 (1998)

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4. Time resolved spectral analysis

The data from TOO1 and TOO2 were divided into 8 and 5 time intervals, respectively, and fitted with the double bremsstrahlung and narrow emission line model (see Table 2). During TOO1 the line parameters (EW and energy, if left free) do not vary significantly between the intervals. The upper limit to any 6.7 keV line shift is 1.4%. The column density, [FORMULA], remains approximately constant. The fluxes of the different model components were calculated for each interval. No significant variation of the fluxes is measured, except that of the hard bremsstrahlung component and the 6.7 keV line, which both decrease smoothly by a factor [FORMULA]1.8.

During the 30 hr observation of TOO2 the energies of the 0.74 and 1.15 keV lines, tentatively identified as blue-shifted O VIII and Ne X /Fe L emission, respectively, both display a regular and significant decrease by 7.7[FORMULA]% and 9.6[FORMULA]%. Changes in the underlying continuum are unlikely to be responsible for these shifts but cannot be excluded. There is no significant change in [FORMULA], or the energies, fluxes, and EWs of the 1.9, 2.5 and 6.75 keV lines. The upper limit to any shift in the 6.75 keV line is 3.5%. The fluxes in the soft and hard bremsstrahlung components decrease by factors 1.3 and 3, and the fluxes in the two soft lines decrease by a factor 1.8. The EWs of the two soft lines increase then decrease (see Fig. 2). Fig. 3 shows the change in energy of the 0.74 keV line during TOO2.

[FIGURE] Fig. 2. The variation in energy, flux and EW of the 0.74 keV feature during TOO2. The variations in these parameters for the 1.15 keV feature are almost identical

[FIGURE] Fig. 3. The change in the 0.74 keV feature between TOO2 intervals 1 and 5. The two solid lines show the subtracted continua, changes in which cannot account for the observed shift

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© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998