\begin{table}%t2
\caption{\label{Observations}Observation log of the {\it ROSAT}, {\it XMM-Newton} and {\it Swift} pre-nova observations. Apart from the exposure time the count rates in different energy bands as well as the absorbed fluxes are given (see text for more details).}
\par
\small%\centerline
 {
\begin{tabular}{c c c c c c c c}      
\hline\hline       
%&&&&&&&& \\[-8pt]
Date & Days     & Instrument & Exposure time  & Count rate$^1$ & Count rate    & Count rate    & 0.2--10.0 keV flux$^2$    \\ 
     & before   &          &    (ks)      & (cts/ks)     & (cts/ks)    & (cts/ks)    &  ($10^{-12}$~erg~cm$^{-2}$~s$^{-1}$)    \\ 
     & outburst &          &                &                & 0.3--1.0~keV  & 1.0--8.0~keV  &  absorbed                        \\
\hline
%&&&&&&&& \\[-8pt]
   1990-10-19 & 6383 & {\it ROSAT}/PSPC[1RXS]& 0.39   & 28 $\pm$ 11 & --- & ---                            & $\rm 4.5^{+19.5}_{-1.8}$ \\
   1993-10-05 & 5302 & {\it ROSAT}/PSPC[2RXP]& 4.3    & 22 $\pm$ 3  & 12 $\pm$ 2 & 8 $\pm$ 2                     & 0.3 $\pm$ 0.1 \\  	      			    2006-11-15 & 517  & {\it XMM-Newton}/EPIC & 3.43 $\times$ $10^{-3}$  & $\rm 1173^{+613}_{-587}$  & --- & ---  & $\rm 2.5^{+7.0}_{-1.6}$ \\  	      	
   2007-05-25 & 322  & {\it Swift}/XRT       & 1.06  & 21 $\pm$ 5  & $\rm 1.9^{+1.9}_{-1.3}$  & $\rm 20^{+5}_{-4}$   & $\rm 5.5^{+8.5}_{-1.4}$   \\  	
   2007-06-10 & 306  & {\it Swift}/XRT       & 0.97  & 41 $\pm$ 7    & $\rm 11.8^{+4.2}_{-3.6}$ & $\rm 31^{+7}_{-6}$ & $\rm 10.7^{+16.5}_{-2.2}$   \\
   2007-07-17 & 269  & {\it Swift}/XRT       & 3.82  & 23 $\pm$ 3    & $\rm 3.5^{+1.3}_{-1.1}$  & 19 $\pm$ 3       & 1.0 $\pm$ 0.2  \\
   2007-07-21 & 265  & {\it Swift}/XRT       & 4.87  & $\rm 37^{+3}_{-4}$ & 27.9 $\pm$ 3.2 & 9 $\pm$ 2             & 0.8 $\pm$ 0.2 \\  
   2008-01-02 & 100  & {\it Swift}/XRT       & 5.65  & 24 $\pm$ 2    & 3.9 $\pm$ 1.0 & 20 $\pm$ 2                & $\rm 1.6^{+0.5}_{-0.4}$    \\[2pt]    
\hline                  
\end{tabular}}
\medskip
Note 1: energy bands: {\it ROSAT/PSPC}, 0.2--2.0~keV; {\it XMM-Newton}/EPIC, 0.2$-$12~keV; {\it Swift}/XRT, 0.3$-$10~keV. \\
Note 2: for the second ROSAT observation, the {\it XMM-Newton} and the first two {\it Swift} observations, the flux was calculated using a power-law with $\Gamma$ between 1.3 and~5.2, and $N_{\rm H}=2.2$~$\times$ $10^{21}$~cm$^{-2}$.
\end{table}