\begin{table}%t1
\caption{King function PSF coefficients determined from piled-up sources used
in the centroiding simulations.} 
%\centerline
{\begin{tabular}{ccrc}
\hline\hline
Target/Obsid & Count rate$^a$ & $r_{\rm c}^b$ & $\beta$ $^c$\\\hline
3c273/00050900011 & 2.31 & 11.88 & 1.63 \\
GK Per/00030842017 & 1.30 & 8.85 & 1.49 \\
GK Per/00030842013 & 0.84 & 7.21 & 1.46 \\
\hline
\end{tabular}}\smallskip
\par
$^a$ Observed PC mode grade 0--12 count rate in a 30 pixel extraction
circle.
$^b$ Core radius (arcsec).
$^c$ Index.
\label{pileup_sim}
\end{table}