\begin{table}%t1
%\setlength{\tabcolsep}{3pt}
%\begin{center}
\par
  \caption{Results of spectral analysis. Errors are at the  90\% c.l. for a single interesting parameter. }
\label{spectra}
    \begin{tabular}[c]{cccclc}
\hline\hline
\nh\   & $\Gamma$      &  $kT_{BB}$   & $R_{BB}$ & \multicolumn{1}{c}{2--10 keV flux} & $\chi^2_{\rm red}$ (d.o.f.) \\
 (10$^{22}$ cm$^{-2}$) & & (keV) & (km)$^{(a)}$ & \multicolumn{1}{c}{(\ferg)}&  \\\noalign{\smallskip}
\hline 
 $\rm 6.8^{+0.4}_{-0.1}$ & $\rm 1.68^{+0.10}_{-0.04}$ & --- & ---& ~$1.91\times10^{-11}$& 1.49 (72) \\\noalign{\smallskip}
 $6.0\pm0.2$ & $\rm 0.8^{+0.2}_{-0.3}$ & $\rm 0.91^{+0.14}_{-0.05}$ & $\rm 1.9^{+0.2}_{-0.3}$ & ~$1.92\times10^{-11}$& 1.02 (70) \\\noalign{\smallskip}
 $6.6\pm0.2$$^{(b)}$ & $\rm 1.42^{+0.08}_{-0.07}$$^{(b)}$ & $\rm 0.69^{+0.06}_{-0.07}$$^{(b)}$ & $\rm 2.1^{+0.5}_{-0.9}$$^{(b)}$ & ~$1.93\times10^{-11}$$^{(b)}$& 0.96 (358)$^{(b)}$ \\
\hline
\end{tabular}
%\end{center}
\par
$^{(a)}$ Radius at infinity assuming a distance of 15 kpc.\\
$^{(b)}$ Simultaneous fit to the five \xmm\ observations with only
the power-law\\ photon index and normalization free to vary independently.
\end{table}