\begin{table}%T7
\caption{\label{counts}QSO~2 surface density.}
%\centering
\par
\begin{tabular}{lrrrrrr}
\hline\hline
$f_{\rm} (0.5{-}8~{\rm keV})$ & \multicolumn{3}{c}{$N$} & \multicolumn{3}{c}{$N$($>$$f_{\rm x})$} \\
  & Known & Candidate & Total & Known & Candidate & Total \\ 
erg cm$^{-2}$ s$^{-1}$ & & & & \multicolumn{3}{c}{deg$^{-2}$} \\
\hline
$1 \times 10^{-15}$ & 9 & 25 & 34 & $\rm 89^{+40}_{-29}$ & $\rm 247^{+60}_{-49}$ & $\rm 335^{+68}_{-57}$ \\
$2 \times 10^{-15}$ & 9 & 14 & 23 & $\rm 89^{+40}_{-29}$ & $1\rm 38^{+48}_{-36}$ & $\rm 227^{+58}_{-47}$ \\
$5 \times 10^{-15}$ & 7 & 3 & 10 & $\rm 69^{+37}_{-25}$ & $\rm 30^{+29}_{-16}$ & $\rm 99^{+42}_{-31}$ \\
$1 \times 10^{-14}$ & 3 & 1 & 4 & $\rm 30^{+29}_{-16}$ & $\rm 10^{+23}_{-8}$ & $\rm 39^{+31}_{-19}$ \\
\hline
\end{tabular}
\end{table}