\begin{table}%t3
\caption{Observed fluxes inferred from observations at different epochs.\label{flux}}
\small%\centerline
{
\begin{tabular}{lccl}
\hline\hline
Observations  & $F_{X}$ (0.1--2.4~keV) & $F_{X}$ (0.5--10~keV) & Start Date\\
              & ergs cm$^{-2}$ s$^{-1}$ & ergs cm$^{-2}$ s$^{-1}$ & 
\\
\hline\noalign{\smallskip}
XMM1         & $3.37^{+0.28}_{-0.26}\times10^{-12}$ & $4.19^{+0.39}_{-0.36}\times10^{-12}$   & 2001-04-15\\\noalign{\smallskip} 
XMM2         & $3.38^{+0.30}_{-0.28}\times10^{-12}$ & $4.17^{+0.42}_{-0.37}\times10^{-12}$   & 2001-11-08\\ \noalign{\smallskip}
Chandra ACIS & $3.34^{+0.40}_{-0.36}\times10^{-12}$ & $4.18^{+0.54}_{-0.50}\times10^{-12}$   & 2000-01-01\\ \noalign{\smallskip}
ROSAT PSPC $^{{\rm a}}$   & $\sim$$3\times10^{-12}$  &  --  & 1991-04-16\\
\hline
\end{tabular}}
\smallskip
$^{{\rm a}}$ Flux observed by ROSAT according to PBW96.
\end{table}