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Astron. Astrophys. 363, 863-868 (2000)

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3. Data analysis and results. Temporal analysis

The LECS (0.1-10 keV) and MECS (1.5-10 keV) light curves are shown in Fig. 1. The source varies as much as a factor [FORMULA]2 on time-scales of a few thousands of seconds. To search for spectral variability, we have also plotted the (1.5-4)/(0.1-1.5) LECS hardness ratio, and the (4-10)/(1.5-4) MECS hardness ratio. Clearly, there is significant spectral variability, especially in the second part of the observation. To investigate the energy dependence of this variability, we calculated the Normalized Excess Variance (NEV; see Nandra et al. 1997) (Fig. 2) for different energy intervals, using a 128 s binning. The source is variable at all energies, but the amplitude is the highest around 2 keV.

[FIGURE] Fig. 1. From top to bottom: LECS light curve and hardness ratio; MECS light curve and hardness ratio; PDS light curve (background subtracted) and PDS/MECS hardness ratio.

[FIGURE] Fig. 2. The Normalized Excess Variance for different energy intervals.

The PDS light curve and the PDS/MECS ratio are also shown in Fig. 1. The light curve is very variable, the background subtracted PDS count rates sometimes going down to values consistent with zero. The light curve is different from those of the LECS and MECS, suggesting either a strong spectral variability or a significant contamination by the nearby BL Lac, 2A 1219+305.

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© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000