\begin{table}%t1
   %\centering
\par
      \caption{{\it XMM} and {\it Chandra} observation log of 51~Peg.}
        \label{Obslog}
    \begin{tabular}{l l l l r}
    \hline\hline
    Instrument & Configuration & ObsID & Obs. time & GTI (s) \\ \hline
    {\it XMM} MOS1 & full frame/thick filter & 0551020901 & 2008-06-01 11:57:03 2008-06-02 03:17:50 & 55000\\
    {\it XMM} MOS2 & full frame/thick filter & 0551020901 &  2008-06-01 11:57:03 2008-06-02 03:17:55 & 55100\\
    {\it XMM} PN & full frame/thick filter & 0551020901 &  2008-06-01 13:09:38 2008-06-02 03:18:10 & 29000\\
    {\it Chandra} ACIS-S & back-illuminated & 10825 & 2008-12-06 11:03:26 2008-12-06 12:26:26 & 4980\\
    {\it Chandra} HRC-I & imaging & 10826 & 2008-12-06 12:44:54 2008-12-06 14:07:54 & 4924 \\ \hline
    \end{tabular}
   \end{table}