\begin{table}%t6
%\centering
\par
 \caption{\label{tab:sample_L_X}Sample divided into three classes \tt I\rm, \tt II\rm, and \tt III\rm, with respect to the X-ray luminosity $L_{\rm X}$. }
 {\footnotesize\begin{tabular}{l l   c c c}
\hline \hline
\noalign{\smallskip}
 $L_{\rm X}$ & & \#  & \# of \tt A\rm-type arc \\
 class & & clusters & cand. per cluster& \\
\hline
 \tt I \rm   & [$\log(L_{\rm X})\leq44.5$]    & 6 & 0.33 \\
 \tt II \rm  & [$44.5< \log(L_{\rm X})<44.9$] & 8 & 0.5 \\
 \tt III \rm & [$44.9\leq\log(L_{\rm X})$]    & 7 & 3.14 \\
\hline
\end{tabular} }
\end{table}