\begin{table}%t2
\caption{
Pulse periods ($P$) and the upper limits on its first derivatives ($\dot P$).}
\label{tab:spin_period}
%\begin{center}
\par
\begin{tabular}{ l l r@{}l c}
\hline
\hline 
name & Reference time$^{*}$ [MJD] & \multicolumn{2}{c}{$P$ [s]} & $\left|\dot P\right|^{**}$ [s/s]  \\
\hline 
H1  &   52~796.00566  &    $296.78 $&$ \pm   0.04$  & $<$$7 \times 10^{-6}$\\%         &      1.6 \\
H2  &   52~824.25522  &    $296.62 $&$ \pm   0.02$  &$ <$$6.5 \times 10^{-7}$\\%  &      3.7 \\
EI  &   53~154.80607  &    $296.698 $&$\pm   0.003$ &$ <$$4 \times 10^{-9}$\\%         &      0.3 \\
H3  &   53~167.38765  &    $296.69 $&$\pm   0.01$ &$ <$$1.8 \times 10^{-7}$ \\
\hline 
\end{tabular}
\smallskip
{$^{*}$ At the reference time the pulse profile has a minimum in the 15--35~keV energy range.}\\
{$^{**}$ Upper limits are given at the $2\sigma$ confidence level.}
%\end{center}
\par
\end{table}