\begin{table}%t1
%\centering
\par
\caption{\label{average}Average properties of the selected short and long GRBs.}  
\small \begin{tabular}{cccc}
\hline\hline
\noalign{\smallskip}
 &$\langle T_{90}\rangle$ &$\langle P_{50-300} \rangle$ &$\langle F \rangle$\\
  &s    &phot~cm$^{-2}$~s$^{-1}$    & erg~cm$^{-2}$ \\
\hline   \noalign{\smallskip}
79 Long GRBs      &17      &11.5      &$1.7\times 10^{-5}$   \\
79 Short GRBs     &0.73    &11.12     &$3.6\times 10^{-6}$ \\
\hline
\end{tabular}
\par
\end{table}