\begin{table}%t6
\caption{X-ray variability.}
%\centerline
{
%\scriptsize
\begin{tabular}{lcccccccccc}
\hline
\hline
\noalign{\smallskip}
Source &&  \multicolumn{2}{c}{Total} && \multicolumn{2}{c}{Soft} &&  \multicolumn{2}{c}{Hard}  &  HR  \\
\noalign{\smallskip}
  &&$P_{\chi^2}$ &$F_{\rm var}$ && $P_{\chi^2}$ &$F_{\rm var}$ &&  $P_{\chi^2}$ &$F_{\rm var}$ & $P_{\chi^2}$  \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
\noalign{\smallskip}
  NGC~1692  && 0.30 & $0.03\pm0.07$ && 0.10 & $0.07\pm0.05$ && 0.45 & $0.05\pm0.10$ & 0.70\\
\noalign{\smallskip}
\noalign{\smallskip}
 PKS~0625-35 && 0.002 & $0.025\pm0.006$ && 0.02 & $0.027\pm0.009$ && 0.21 & $0.020\pm0.015$ & 0.59 \\
\noalign{\smallskip}
\noalign{\smallskip}
3C~88     && 0.10 & $0.10\pm0.07$ && $<$0.001 & $0.20\pm0.09$ && 0.10 & $0.09\pm0.13$ & 0.07    \\
\noalign{\smallskip}
\noalign{\smallskip}
3C~444    && 0.39 & $0.03\pm0.03$ && 0.23 & $0.06\pm0.03$ && 0.12 & $\dots$ & 0.02     \\
\hline
\end{tabular}}\medskip
  For NGC~1692, PKS~\mbox{0625-35} and 3C~444 the variability results have been obtained using EPIC pn light curves with
time bins of 500 s. For 3C~88, we have used EPIC MOS2 light curves with
time bins of 1000 s, because the EPIC pn data are severely affected by background flaring.
\label{tab6}
\end{table}