All Figures

$\begin{figure} \par\includegraphics[width=16cm,clip]{gfx/2977fig1.eps} \end{figure}$ Figure 1: Light curves of the EPIC MOS1 camera in the three C1, C2 and C3 energy bands (indicated on top of the panels) for two observations representative of the sample and indicated on the right side of the panels. The dashed lines in each panel marks the two sigma level used for the rejection of contaminated time intervals at the final iteration step (see Sect. 3.2). Mean count rates as determined by our programs are shown in the upper parts of the panels as $\mu$ . The arrows (solid, dashed and dotted) point to the effect of three typical proton flares with significant differences in their respective spectra (see Sect. 3.2).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{gfx/2977fig2.eps} \end{figure}$ Figure 2: Hardness ratios of the proton flares detected with our procedure for observations performed with the medium filter (see Sect. 3.2.1). With the energy bands C1, C2 and C3 we make use of the whole EPIC energy coverage. For clarity, we omit the error bars which vary in a broad range. This is because there are significant differences in the respective intensities of the proton flares represented in the figure, from very faint to very bright which correspond to relatively large (about 35%) and small (about 10%) error bars respectively. We can see that the hardness ratios of the proton flares are wide spread in all ranges. In contrast to the suggestions by Lumb et al. (2002); Read & Ponman (2003), there is an important fraction of proton flares with soft and medium spectra in the lower half of the diagram.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{gfx/2977fig3.eps} \end{figure}$ Figure 3: X-ray background map towards the field indicated in the upper part of the panel, as obtained by the standard SAS data reduction tasks: the SAS-calibrated photon image is "source filtered'' (see Sect. 3.4), smoothed and finally corrected by the exposure map calculated by the corresponding SAS task ( eexpmap). The increase in intensity towards the rims of the detector (see inverted tunnel effect in Sect. 4) is created by the use of the task eexpmap. This resulting background map is unacceptable since, at the B4 band, the X-ray background is dominated by the extragalactic background (Read & Ponman 2003) which must yield in very homogeneous intensity distributions.
Open with DEXTER

In the text

$\begin{figure*} \par\includegraphics[width=13cm,clip]{gfx/2977fig4.eps} \end{figure*}$ Figure 4: Normalized mean exposure time vs. radial distance to the optical center of the EPIC MOS2 camera for the four energy bands shown at the upper right part of each diagram. The thick solid line shows our new developed exposure maps. To illustrate the quality of these exposure maps, we also show the background intensity distribution, without correction for vignetting, of four different observations (thin solid lines). The error bars are calculated based on the photon statistics of the inner 5 arcmin of the observations. The solid lines can be compared to the SAS calculated exposure maps (dashed lines) for the corresponding observations and bands. The use of version 5.4.1 of the SAS software and a more modern calibration database (synchronization of March, 2004), as mentioned in Sect. 5, yields only slight variations in the shape of the obtained exposure maps.
Open with DEXTER

In the text

$\begin{figure} \includegraphics[width=11cm,clip]{gfx/2977fig5.eps} \end{figure}$ Figure 5: Normalized exposure maps for the four energy bands indicated on the top of the panels obtained with our method applied to the EPIC MOS1 detector with the medium filter. The grids of each map are presented in detector coordinates. The gaps in the maps correspond to the detector mask. Apart from a small residual contamination from CCD2 (see Sect. 5) in the lower right part of the B1 band map, a good radial symmetry is present in all panels. The total effective exposure times used to calculate the maps of this figure are $t_{\rm eff} \simeq 0.45~ {\rm Ms}$ for B1, $t_{\rm eff} \simeq 0.82~ {\rm Ms}$ for B2 and $t_{\rm eff} \simeq 1.15~ {\rm Ms}$ for bands B3 and B4. The differences in the total times are related to bright CCD contamination (see Sect. 5 and Fig. 9).
Open with DEXTER

In the text

$\begin{figure} \includegraphics[width=11cm,clip]{gfx/2977fig6.eps} \end{figure}$ Figure 6: Normalized exposure maps for the four energy bands indicated on the top of the panels obtained with our method applied to the EPIC MOS2 detector with the medium filter. The grids of each map are presented in detector coordinates. The gaps in the maps correspond to the detector mask. A good radial symmetry is present in all panels. The total effective exposure times used to calculate the maps of this figure are $t_{\rm eff} \simeq 1.15~ {\rm Ms}$ in all cases.
Open with DEXTER

In the text

$\begin{figure} \includegraphics[width=11cm,clip]{gfx/2977fig7.eps} \end{figure}$ Figure 7: Normalized exposure maps for the four energy bands indicated on the top of the panels obtained with our method applied to the EPIC pn detector with the medium filter. The grids of each map are presented in detector coordinates. The gaps in the maps correspond to the detector mask. Like in the case of MOS1 (see Fig. 5), there are clear unexpected asymmetries in the radial distribution of the B1 band vignetting. The total effective exposure times used to calculate the maps of this figure are $t_{\rm eff} \simeq 1.15~ {\rm Ms}$ in all cases.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=11.5cm,clip]{gfx/2977fig8.eps} \end{figure}$ Figure 8: Radial profiles of the exposure maps for the energy bands indicated in the upper right part of the diagrams in the cases of the thin (dotted line), medium (solid line) and thick (dashed line) filters. For clarity, only the error bars for the medium filter are shown. These are calculated based on the variation of the exposure across the rings used for the calculation of the radial profile. There are clear differences in the profiles for the different filters, like for the thick filter in the B2 panel.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{gfx/2977fig9.eps} \end{figure}$ Figure 9: EPIC MOS1 exposure maps calculated for the three separated data sets indicated in the top of each figure for the medium filter. The white grid and numbers shown in the upper panel indicate the positions of the seven CCDs in the MOS1 camera. The maps are normalized to a value of 1 in the center of the map. The count rate increase in the contaminated observations accounts up to a value of 1.5 in the affected region of the normalized exposure map. This corresponds up to a factor of 2 above the uncontaminated case (shown in the upper left panel of Fig. 5).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=13cm,clip]{gfx/2977fi10.eps} \end{figure}$ Figure 10: Upper panels: scatter plots of the CCD2 contamination as defined in Eq. (2) vs. the quantities indicated in the horizontal axes in logarithmic scale. The points with error bars represent contaminated observations (Eq. (1)), where solid squares correspond to observations which also present CCD5 contamination. Empty squares represent uncontaminated observations. The curves correspond to the regression lines of the data. The statistical significance of the regression lines is shown in Table 2. The mean background intensities of the left panel are calculated using the data gained with CCDs 3, 4, 5 and 7. Lower panels: equivalent to the upper panels for the CCD5 contamination. Points with error bars are CCD5 contaminated, solid squares show CCD2 contaminated observations and empty squares represent uncontaminated observations. No regression lines are shown because the statistical tests do not reject the zero correlation hypothesis in any of the three cases shown here (see Table 2 and Sect. 5.1). Visually, the CCD5 contaminated set is well separated from the remaining observations which are located close to the C₅ = 1 line as expected for pointings free of contamination.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{gfx/2977fi11.eps} \end{figure}$ Figure 11: Hardness ratios of the X-ray backgrounds as detected with the EPIC MOS1 camera for the observations in Tables 3 to 6 (all filters). Empty squares correspond to observations free of CCD2 or CCD5 contamination, solid squares to CCD2 contaminated observations and the points with the error bars to CCD5 contaminations. However, in order to avoid the influence of this contamination in the hardness ratios presented here, we calculate the values based only on the data provided by uncontaminated CCDs. The results shown in this figure rule out a correlation between the hardness ratio of the X-ray background towards the observed field and the presence of bright CCD contamination, either for the CCD5 or for the CCD2 case. This can be deduced from the fact that the contaminated observations are spread in the panel with a similar distribution to that of the uncontaminated observations.
Open with DEXTER

In the text