\begin{table}%t6
\caption{\label{tab3}Best fit parameters of the PC grade 0$-$12 spectra extracted using the
40~arcsec core of the SNR~G21.5.}
\par
\small%\centerline
 {
\begin{tabular}{cccc}
\hline \hline
%&&& \\[-8pt]
$V_{\rm ss}$  & $N_{\rm H}$  & $\Gamma$ & Normalisation$^\dagger$\\
 (V) & ($\times 10^{22}$ cm$^{-2}$) & & ($\times 10^{-2}$~ph~keV$^{-1}$~cm$^{-2}$~s$^{-1}$)\\
%    &                              & & ph keV$^{-1}$
%cm$^{-2}$ s$^{-1}$) \\
\hline
%&&& \\[-8pt]
0 & $\rm 3.26^{+0.17}_{-0.16}$ & $1.92\pm 0.07$ & $\rm 1.71^{+0.20}_{-0.18}$$^*$\\
6 & $\rm 3.38^{+0.14}_{-0.13}$ & $2.01\pm 0.06$ & $\rm 1.84^{+0.17}_{-0.15}$$^*$\\
\hline
\end{tabular}}
\medskip
$^\dagger$ The fits were performed using a {\scriptsize TBABS*POWERLAW} model with the abundance table given by Wilms et~al. (\cite{Wilm00}). No PSF~correction was applied since the source is extended. \\ 
$^*$ All the errors quoted above are given at~$2.71\sigma$.
\end{table}