\begin{table}%t1
\caption{\label{tab:ground-state}Ionic column densities of neutral and singly ionized species
  at the \grb-DLA redshift of $z_{\rm abs}=3.96857$.}
%\centerline
 {
\begin{tabular}{lllcc}
\hline
\hline\\[-3.2mm]
Ion          &
Energy level &
Transition   &
${\log N\pm\sigma _{\log N}}^{b}$\\
&& lines used (\AA )&\\
\hline
\multicolumn{4}{l}{1st epoch of observations:}\\
C$^0$  & g.s.$^{a}$                & 1277        &     ${<}13.05^{c}$\\
N$^0$  & g.s.$^{a}$                & 963, 1134.1 &     $14.77\pm 0.03$   \\
S$^+$  & g.s.$^{a}$                & 1250, 1253  &     $15.11\pm 0.04$   \\
Ar$^0$ & g.s.$^{a}$                & 1066        &     $14.36\pm 0.05$   \\
Ni$^+$ & g.s.$^{a}$                & 1317        &     $13.53\pm 0.05$   \\
\hline
\multicolumn{4}{l}{2nd epoch of observations:}\\
Si$^+$ & g.s.$^{a}$ ($^2{\rm P}_{1/2}$) & 1808        &     $15.47\pm 0.03$   \\
Si$^+$ & $^2{\rm P}_{3/2}$                 & 1816, 1817  &     ${<}15.55^{d}$\\
Ni$^+$ & g.s.$^{a}$                & 1370, 1751  &     $13.69\pm 0.02$   \\
\hline
\end{tabular}}
\medskip
\par
$^{a}$ Ground state. 
$^{b}$ Listed uncertainties are the formal errors provided by FITLYMAN. 
$^{c}$ $3\sigma$ upper limit. 
$^{d}$ Blend with telluric absorption.
\end{table}