\begin{table}%t1
%\centering
\par
\caption{\label{tab:perhist}Pulse period values obtained with archival \textit{INTEGRAL} data.}
\begin{tabular}{llll}
\hline \hline\noalign{\smallskip}
{MJD$_{\rm obs}$} & {Period,~s.} & {MJD$_{\rm obs}$} & {Period,~s.}\\
\hline
 52833.5 & $681.33\pm0.04$ & 53538.0 & $684.59\pm0.12$\\
 53088.0 & $683.42\pm0.07$ & 53541.6 & $684.4\pm0.04$\\
 53525.9 & $683.9\pm0.1$ & 53545.6 & $684.27 \pm 0.04$\\
 53528.5 & $684.19\pm0.16$ & 53549.4 & $684.15\pm0.05$\\
 53529.7 & $684.15\pm0.44$ & 54111.9 & $684.62\pm0.06$\\
 53535.0 & $684.73\pm0.05$ & 54277.6 & $685.15\pm0.07$\\
\hline
\end{tabular}
\tablefoot{An updated ephemeris was used to correct the lightcurve for binary motion. The error is estimated as 10\% of the width of the peak in the periodogram.}
\end{table}