\begin{table}%t4
 \caption{\label{tab:sed}SED modelling of  PKS 0521-365 components.}
%%\centerline
 {\small 
\par
 \begin{tabular}{cccccc}
\hline\hline\noalign{\smallskip}
 & $\alpha_0^a$ & $R_0^b$   & $n_0^c$   & $B^d$  &  $\nu_{\rm c}^e$   \\
\hline\noalign{\smallskip}
nucleus   &   0.9        & $1.5 \times 10^{-6}$ & 95~000    & 30    & $1.0 \times 10^{13}$  \\
knot A   &   0.7        & 0.5                  & $1.3 \times 10^{-4}$ & $9.5 \times 10^{-5}$ & $1.0 \times 10^{14}$  \\
knot D   &   0.7        & 0.5                  & $6.2 \times 10^{-5}$ & $6.9 \times 10^{-5}$ & $5.8 \times 10^{13}$  \\
hotspot  &   0.8        & 0.5                  & $5.8 \times 10^{-3}$ & $5.3 \times 10^{-4}$ & $3.0 \times 10^8$  \\
 \hline
 \end{tabular}}
 \medskip
$^a$ Spectral index below $\nu_{\rm c}$; $^b$~size of emitting region in kpc; $^c$~plasma density, i.e. number of particles per~cm$^3$; $^d$~magnetic field in Gauss; $^e$~cooling frequency in~Hz.
\end{table}