\begin{table}%t2
\caption{\label{tab2}Spectral parameters of the best-fit model inferred from the Chandra observed spectra of \G.}
%\centerline
 {\small  
\begin{tabular}{l c c}
\hline\hline
& The Northern rim & The Southern rim \\
\hline \noalign{\smallskip}
$n_{\rm H}$ ($10^{21}$~cm$^{-2}$) &  $4.1 \pm 0.9$  & $\rm 5.9^{+1.2}_{-1.1}$\\ 
$T$ ($10^{6}$~K)  &  $\rm 6.6^{+0.5}_{-0.7}$  & $7.0\pm0.7$ \\ 
Mg  &  $\rm 2.6^{+0.9}_{-0.7}$ & $\rm 1.7^{+1.1}_{-0.7}$ \\ 
Si  &  $\rm 2.8^{+1.5}_{-1.2}$ & $\rm 4.7^{+2.6}_{-1.7}$ \\ 
S &  $\rm 13.6^{+8.7}_{-6.9}$  & $\rm 16.2^{+11.7}_{-7.4}$ \\ 
Norm$_{\rm cie}$ ($10^{-4}$)$^{a}$ & $\rm 1.4^{+0.6}_{-0.4}$  & $\rm 1.0^{+0.5}_{-0.4}$ \\ 
%\hline
$E_{1}$ (keV) & $4.0\pm0.2$ & -- \\ 
$\sigma_{1}$ (keV)& $\rm 0.3^{+0.2}_{-0.1}$ & -- \\ 
Norm$_{\rm gauss1}$ ($10^{-6}$)$^{b}$& $\rm 3.3^{+1.4}_{-1.3}$& -- \\ 
%\hline
$E_{2}$ (keV)& $\rm 7.3^{+3.2}_{-0.5}$  &  7 (fixed)  \\ 
$\sigma_{2}$ (keV)  & $\rm 0.9^{+2.0}_{-0.3}$  & $\rm 1.1^{+0.4}_{-0.3}$\\ 
Norm$_{\rm gauss2}^{b}$ ($10^{-5}$)$^{b}$ & $\rm 2.9^{+12.7}_{-1.4}$& $1.4\pm0.5$\\ 
\chisq\   &  25.41  & 31.37  \\ 
d.o.f.    &  29  &  23 \\ 
 \hline
 \end{tabular}}
\smallskip
$^{a}$~The normalization of CIE model is expressed as 
$(10^{-14}/4\pi D^{2})\int N_{\rm e}N_{\rm H}{\rm d}V$ where $D$ is the source distance in cm and $N_{\rm e}$ and $N_{\rm H}$ are the post-shock electron and hydrogen densities in~cm$^{-3}$; $^{b}$~the normalization of the Gaussian model is in unit of photon~cm$^{-2}$~s$^{-1}$. 
 \end{table}