\begin{table}%t1
\caption{\label{tab.spectral_results}Results of XRT observations of 3C~279. Power law model with $N_{\rm H}$ fixed to the Galactic value of $2.05$~$\times$ $10^{20}$~cm$^{-2}$.}
%\centering
\small
\begin{tabular}{cccc}
\hline \hline
&&& \\[-8pt]
\multicolumn{1}{c}{Observation} &
\multicolumn{1}{c}{Flux 2$-$10 keV} &
 \multicolumn{1}{c}{Spectral slope} &
 \multicolumn{1}{c}{$ \chi^{2}_r$ (d.o.f.)} \\
 \multicolumn{1}{c}{date}&
 \multicolumn{1}{c}{erg cm$^{-2}$ s$^{-1}$} &
 \multicolumn{1}{c}{$\Gamma$}&
 \multicolumn{1}{c}{}\\
\hline
&&& \\[-8pt]
10-Jul.-2007 & 1.20 $\times$ $10^{-11}$ & $1.42 \pm 0.05$ &1.21 (73)\\
11-Jul.-2007 & 1.17 $\times$ $10^{-11}$ & $1.47 \pm 0.07$ &0.86 (52)\\
12-Jul.-2007 & 1.05 $\times$ $10^{-11}$ & $1.47 \pm 0.06$ &1.07 (57)\\
13-Jul.-2007 & 1.13 $\times$ $10^{-11}$ & $1.48 \pm 0.06$ &0.96 (50)\\
\hline
\end{tabular}
\end{table}