\begin{table}%t3
\caption{\label{x-flux}Comparison between X-ray fluxes from the literature and from
  this work.}
  %\centerline
$$
\begin{tabular}{@{}lccccc@{}}
\hline\hline
Data & Obs.\ date & \multicolumn{3}{@{}c@{}}{Flux}  & Ref. \\
\cline{3-5}
 & & \multicolumn{2}{@{}c@{}}{Soft} & \multicolumn{1}{@{}c@{}}{Hard} & \\
 & & 0.1--2~keV & 0.1--2.4~keV & 2--10~keV & \\
\hline	
EXOSAT & 1984 Nov.\ & 4.2 &  --  & 5.6  & 1 \\
EXOSAT & 1985 Nov.\ & 9.5 &  --  & 6.3  & 1 \\
GINGA  & 1989 Nov.\ & --  &  --  & 4.7  & 2 \\
ROSAT  & 1990 Nov.\ & --  & 33.1 & --   & 3 \\ 
XMM    & 2003 May   & --    &  --  & 3.63 & 4 \\[1pt]
XMM    & 2003 May   & ${2.70_{-0.08}^{+0.19}}$ & $3.00\pm 0.08$ & ${3.65_{-0.08}^{+0.07}}$ & 5 \\[2pt]
XMM    & 2006 May   & ${16\pm 2} ^{a}$ & -- & ${10\pm3} ^{b}$ & 6 \\
\hline 
\end{tabular}
$$
\par
Fluxes are given in
  $10^{-12}$~\fluxunits. $^{a}$~Flux between 0.2--2~keV. $^{b}$~Flux between 2--12~keV. 
  References: (1) \cite{1991ApJ...372...49Singh}; 
  (2) \cite{1992ApJ...389..157Williams}; (3) Voges et al.\ (1999); 
  (4) \cite{2007ApJ...662..860Inoue}; (5) this work; 
  (6) XMM-Newton slew survey Source Catalogue (Saxton et al.\ 2008).
\end{table}