\begin{table}%t2
\caption{Summary of the observational parameters for the two frequencies used for our observations.
\label{tbl:radio_setup}}
%\centerline
 {\begin{tabular}{lcc}
\hline
\hline
Parameter& 3.6 cm & 6 cm \\
\hline
Rest frequency (MHz)  & 8640 & 4800 \\
Bandwidth (MHz) & 128    & 128 \\
Primary beam   & 5\farcm5 & 9\farcm9 \\
Synthesised beam$^a$    & $\sim$1\farcs5& $\sim$2\farcs5 \\
Largest well imaged structure$^a$  & $\sim$20$^{\prime\prime}$ &$\sim$30$^{\prime\prime}$\\
Theoretical image rms (mJy beam$^{-1}$)  & 0.21 & 0.22\\
Typical image rms (mJy beam$^{-1}$)$^b$  & 0.32 & 0.27 \\
Image pixel size  &  0\farcs33 & 0\farcs6\\
\hline
\end{tabular}}
\par
\smallskip
$^a$ Declination and hour angle dependent;
$^b$ the stated rms values have been estimated from emission free regions close to the centre of maps presented in Fig.~3 (see Sect.~\ref{sect:results}). 
\end{table}