\begin{table}%t1
\caption{PCA observations of 4U 1820--30 analyzed in this work.}\label{tab1}
%\centering
\par
\begin{tabular}{lccc}
\hline
\hline
Obs.   &  Start date & Start time & Exp. (s)\\ \hline
A      &  1996-May-4 & 17:06      & 3512    \\
B      &  1997-Jul.-16& 5:12       & 3640    \\
\hline
\end{tabular}
\end{table}