\begin{table}%t1
\caption{Short-term X-ray variability of \object{NGC~6251}.}\label{table:shortvar}
%\centerline
{
\begin{tabular}{ccccc}
\hline
\hline
Energy band & $\langle r\rangle$ & $\chi^2_{\rm red}$ 
&  $P_{\chi^2}$ & $F_{\rm var}$ ${^a}$ 
\\ 
(keV) & (${\rm s^{-1}}$) & (14 d.o.f.) & (\%) & (\%)\\
\hline
0.4--0.7 keV  & 0.49&  0.54 & 89.6 & $-$   \\
0.8--1 keV  & 0.34&  1.40 & 14.8 & $2.2\pm1.4$   \\
1.2--1.5 keV  & 0.36  & 1.48 & 11.7 & $2.1\pm1.3$   \\
1.8--3 keV   & 0.41   & 1.59 & 8.1 & $2.3\pm1.2$   \\
3--10 keV   & 0.39    & 1.66 & 6.2 & $2.8\pm1.3$   \\
\hline
\end{tabular}}
\medskip
${^a}$ The errors on $F_{\rm var}$ are calculated as in
Edelson et~al. (\cite{Ede02}) and should be considered conservative estimates
of the true uncertainty. 
\end{table}