\begin{table}%t1
\caption{Observation log for the data used in the analysis of
  GRB~050510 and GRB~050512.  }
\label{tab1} 
%\centering
\small
\begin{tabular}{cccr}
\hline \hline
Obs. \# & \multicolumn{1}{c}{Start time (UT)} & \multicolumn{2}{c}{Exposure} \\
                  & (yyyy-mm-dd hh:mm:ss) &   WT (s) & \multicolumn{1}{c}{PC (s)} \\
\hline
\multicolumn{4}{l}{{\it GRB~050410 }} \\
1  & 2005-04-10~12:46:24 & 9436 & 8635 \\
2  & 2005-04-12~16:15:47 &  --  & 4740\\
3  & 2005-04-12~00:11:47 &  --  & 1473\\
4  & 2005-04-14~00:22:44 & --   & 3184\\
5  & 2005-04-15~00:30:44 & --   & 10~895\\
6  & 2005-04-16~00:32:01 & --   & 13~086\\
7  & 2005-04-17~16:45:01 & --   & 6418\\
8  & 2005-04-19~00:50:42 & --   & 9832\\
9  & 2005-04-20~00:54:29 & --   & 11~123\\
10 & 2005-04-21~00:55:58 & --   & 1828\\
 & Total exposure (s)             & 9436 &  71~214   \\
\multicolumn{4}{l}{{\it GRB~050412 }} \\
1  &2005-04-12~05:45:47  & 3019 & 1950 \\
2  &2005-04-14~00:04:59  & --   & 3719 \\
3  &2005-04-17~09:28:35  & --   & 6200 \\
 & Total exposure (s)       & 3019 &11~869 \\   
\hline
\end{tabular}
\end{table}