\begin{table}%t1
%\centering
\par
\caption{\label{table_periods}
Results of HESS\ observations on PSR~B1259$-$63. For each
darkness period the number of telescopes used in the analysis
$N_{{\rm tel}}$, the live time $t_{{\rm live}}$, the
significance $S$ calculated according to \citet{LiMa}, the number of
counts within the on-source ($N_{{\rm on}}$) and off-source
($N_{{\rm off}}$) region(s), the background normalisation $\alpha$,
and the number of detected $\gamma$-rays ($N_{{\rm \gamma}}$) are
listed. The background normalisation $\alpha$ was determined by the
number of off-regions, which do not coincide with other $\gamma$-ray
sources in the field of view. Therefore $\alpha$ is not the same for
all data subsets because it depends on the distribution of wobble
offsets used when obtaining the data.}
{{\begin{tabular}{crrrrrrr}
\hline\hline
Period & $N_{{\rm tel}}$ & $t_{{\rm live}}$ & $S$ & $N_{{\rm on}}$ & $N_{{\rm off}}$ & $\alpha$ & $N_{{\rm \gamma}}$\\
2004 & & [h] & [${\rm \sigma}$] & & & &\\
\hline
February & 3 & 7.9  & 9.8  & 691    & 2~591  & 0.172 & $246\pm25$ \\
March    & 4 & 17.8 & 7.2  & 1~740 & 8~459  & 0.169 & $307\pm43$ \\
April    & 4 & 5.1  & 7.8  & 644    & 2~705  & 0.167 & $193\pm25$ \\
May      & 4 & 9.9  & 5.2  & 910    & 4~499  & 0.167 & $160\pm31$ \\
June     & 4 & 9.1  & 1.8  & 722    & 4~027  & 0.167 & $ 51\pm28$ \\
\hline
Total    &   & 49.8 & 13.8 & 4707 & 22~281 & 0.168 & $955\pm69$\\
\hline
\end{tabular}}}
\end{table}