\begin{table}%t1
%\centering
\par
\caption{XMM-{\em Newton} and {\em Chandra} net number of counts (background 
subtracted) collected by each instrument in the specified\protect extraction region 
and spectral range.}
\label{counts}
   \begin{tabular}{llll}
\par
    \hline\hline 
\par
     \bf{Instrument} & \bf{Extraction} & \bf{Energy} & \bf{Net number} \\
      & \bf{region} & \bf{[keV]} & \bf{of counts} \\    
     \hline
\par
    {\it  XMM-Newton} & & & \\ 
    PN & $50''$ & $0.3{-}10$ & $1680$ \\
    MOS 1 & $50''$ & $0.3{-}10$ & $590$ \\
    MOS 2 & $50''$ & $0.3{-}10$ & $520$ \\
      \hline
\par
     {\it Chandra} & & & \\ 
     ACIS-S & $10''$ & $0.3{-}10$ & $1990$ \\
     ACIS-S & ellipse & $0.3{-}2$ & $530$ \\ 
       \hline
\end{tabular}
\end{table}