Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{Hk181_f1.ps} \end{figure}$ Figure 1: Differences in coordinates (RA in the upper panel, Dec in the lower) between the XRT and optical positions (X-optical). We used both catalogued sources and GRB observations with well known optical counterpart. The plotted errors are the combination of the statistical errors and the aspect solution uncertainty. The solid line is the fit to the entire sample, the dashed line is the fit relative to the catalogued sources only and the dotted line is the fit to the afterglows: the best fit parameters are perfectly consistent. RA residuals have been corrected by the factor cos(Dec), and represent the true separation in the sky.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{Hk181_f2.ps} \end{figure}$ Figure 2: The residuals of the 43 sources with more than 1000 counts before (black) and after the correction (grey). The contour of the two dimensional Gaussian best fit function are over-plotted in correspondence of 10%, 50%, 90% of the maximum value. The external panels show the distribution of the coordinate residuals before and after the correction together with their best Gaussian fit.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{Hk181_f3.ps} \end{figure}$ Figure 3: The integral distribution of the distances of the X-ray sources, with more than 1000 counts, from the optical counterpart before (black lines) and after the correction (grey lines). The dotted line is the the integral of the best Gaussian fit to the distribution of the coordinate residuals (see Fig. 2).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{Hk181_f4.ps} \end{figure}$ Figure 4: A VLT+ISAAC J filter image of GRB 050904. The lines show the position of the optical afterglow. The dashed circle is the original error circle, while the smaller and solid line circle is the refined one. The optical transient is at 1.6 $^{\prime \prime }$ from the refined XRT position and at 6.2 $^{\prime \prime }$ from the original position quoted in Mineo et al. (2005). As it is clear from the distribution of the residuals (Fig. 3), this represents an extreme case: only 15% of the positions are expected to be at more than 6 $^{\prime \prime }$ from the optical position before the correction. The image is taken from Tagliaferri et al. (2005).
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{Hk181_f2.ps} \end{figure}$	Figure 2: The residuals of the 43 sources with more than 1000 counts before (black) and after the correction (grey). The contour of the two dimensional Gaussian best fit function are over-plotted in correspondence of 10%, 50%, 90% of the maximum value. The external panels show the distribution of the coordinate residuals before and after the correction together with their best Gaussian fit.
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$\begin{figure} \par\includegraphics[width=7.6cm,clip]{Hk181_f3.ps} \end{figure}$	Figure 3: The integral distribution of the distances of the X-ray sources, with more than 1000 counts, from the optical counterpart before (black lines) and after the correction (grey lines). The dotted line is the the integral of the best Gaussian fit to the distribution of the coordinate residuals (see Fig. 2).
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