\begin{table}%t2
\caption{\label{tab2}Data on X-ray nuclear emission used for the SED 
(see the Appendix for details).}
%\centerline
{
\begin{tabular}{cccc}
\hline\hline\noalign{\smallskip}
Source    & $L^{a}_{\nu {\rm X}}$ & $\alpha_{\rm X}$ &  Instrum. (refer.)   \\
\noalign{\smallskip}\hline\noalign{\smallskip}
3C~~29    & $5.5^{\star}$       & 1.0                   & PSPC (1)      \\
3C~~31    & 0.46                & $\rm 0.5^{+0.3}_{-0.2}$     & Chandra (2)  \\
3C~66B    & $\rm 9.5^{+0.2}_{-0.9}$ & $\rm 0.3^{+0.3}_{-0.4}$   & PSPC (1) \\
3C~~78    & $\rm 32^{+10}_{-17}$    & 1.0                   & SAX (3)      \\
3C~83.1   & $3.6^{\star}$       & 1.0                   & PSPC (4)       \\
3C~~189   & 14                  & $\rm 1.1^{+0.1}_{-0.4}$   & Chandra (5)  \\
3C~272.1  & $\rm 0.051^{+0.003}_{-0.003}$ & $\rm 1.3^{+0.1}_{-0.1}$   & Chandra (6)       \\
3C~277.3  & $<$$5.3$              & 1.0                   & PSPC (1)        \\
3C~288    & $<$$2100$             & 1.0                   & PSPC (4)        \\
3C~296    & $6.0^{\star}$       & 1.0                   & HRI (4)        \\
3C~310    & $16^{\star}$        & 1.0                   & HRI (4)        \\
3C~317    & $\rm 30^{+21}_{-23}$    & $\rm 0.1^{+0.3}_{-0.7}$   & PSPC (1)        \\
3C~338    & $\rm 0.53^{+0.11}_{-0.11}$ & $\rm 0.5^{+0.5}_{-0.4}$   & Chandra (7)        \\
3C~346    & $\rm 618^{+110}_{-160}$    & $\rm 0.7^{+0.2}_{-0.2}$   & ASCA (8)      \\
3C~348    & 234                 & 1.0                   & PSPC, ASCA, SAX (9)  \\
3C~442    & $<$$1.9$              & 1.0                   & HRI (4)       \\
3C~449    & $0.89^{\star}$      & 1.0                   & PSPC (4)        \\
\hline
\end{tabular}} 
\smallskip
$^{a}$ $\times 10^{16}$ W Hz$^{-1}$ (at 1~keV). For each object $N_{\rm H}$
is fixed to its galactic value, except for 3C~272.1 where it is deduced from the fit 
($N_{\rm H} = 2.7^{+0.3}_{-0.3} \times 10^{21}$~cm$^{-2}$). In the 
sources marked with $^{\star}$ contamination from thermal emission may 
be present.\\
%\smallskip
\noindent References: (1) this work; (2) Hardcastle et~al. (\cite{Hardcastle2002}); (3) Trussoni et~al. (\cite{Trussoni1999}); (4) HW99; (5) Worral et~al. (2001); (6) Finoguenov \& Jones (\cite{Finoguenov});  (7) Di~Matteo et~al. (\cite{Matteo2000});  (8) Worrall \& Birkinshaw (\cite{Worrall2001}); (9) Siebert et~al. (\cite{Sieber}), Trussoni et~al. (\cite{Trussoni2001}).
\end{table}