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 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.
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.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000