\begin{table}%t5
  \caption{\label{pindex}Power-law indices for the regions in M~101 and M~81.}
%\centering
\par
   \begin{tabular}{cccccccc}   
     \hline \hline 
            Object & Region & Power-law index  \\ \hline
            M~101&Spiral arms &$2.2\pm0.2$ \\
            &Giant \ion{H}{ii} regions & $1.0\pm0.5$ \\ \hline
            M~81&Spiral arms &$1.9\pm0.4$ \\ \hline
 \end{tabular} 
\end{table}