\begin{table}%t2
   %\begin{center}
\par
     \caption{Summary of the chracteristics of the principal
     populations of the IBIS-ISGRI sources in terms of their
     distributions above the Galactic Plane.}
     \label{tab:scales}
     $$
    \begin{tabular}{lr@{$~\pm~$}lr@{$~\pm~$}lc} \hline\hline
                       &  \multicolumn{2}{c}{$k$} & \multicolumn{2}{c}{$\alpha$} & Scale height (pc) \\
      \hline
      HMXBs             &   9 & 3  & 4 & 1   & 240$^{+90}_{-40}$ \\
      LMXBs             &   13 & 3  & 2.9 & 0.6 & 350$^{+90}_{-60}$ \\
      Unclassified sources              &   12 & 3  & 4 & 1   & 240$^{+90}_{-40}$ \\
      \hline
      \end{tabular}
      $$
     %\end{center}
\par
   \end{table}