\begin{table}%t3
\caption{X-ray properties of the GRBs with known redshift and
data collected from the literature. $\alpha$ and~$\beta_{\rm X}$ are the temporal and spectral
power~law indices, respectively [i.e. $F(\nu,t)\propto t^{-\alpha}\nu^{-\beta_{\rm X}}$]. 
$F_{\rm X}$~is the observed X-ray flux integrated in the reported energy band and $L_{10~{\rm keV}}^{12~{\rm h}}$ is the monochromatic X-ray luminosity at~12~h (rest frame) calculated at~10~keV.}\label{tabx}
\small%\centerline
{
\begin{tabular}{l l c c c c c c c}
\hline\hline
GRB &$z$ &$\alpha$ & $\beta_{\rm X}$ & $F_{\rm X}$         & $t_{\rm obs}$ & band &
$\log L_{10~{\rm keV}}^{12~{\rm h}}$ & Ref. \\ 
    &    &         &           &$10^{-12}$ cgs &             & keV  & & \\
\hline
\object{970228} &0.695$^1$ &1.3 $\pm$ 0.1   &1.1 $\pm$ 0.3   &1.0 $\pm$ 0.2    &1d   &2--10
  &26.81 & co97 \\  
970508 &0.835 &1.1 $\pm$ 0.1$^a$ &1.1 $\pm$ 0.3   &1.0 $\pm$ 0.4    &1d
  &2--10 &26.97 & gb05, pi98\\ 
971214 &3.418 &1.1 $\pm$ 0.1  &1.2 $\pm$ 0.4  &0.23 $\pm$ 0.05 &1d   &2--10
  &27.47 & co99, gb05\\ 
980613 &1.096 &1.1 $\pm$ 0.2   &1            &0.27 $\pm$ 0.07  &1d   &2--10
  &26.63 & co99\\   
980703 &0.966 &0.9 $\pm$ 0.2   &1.8 $\pm$ 0.4   &0.48 $\pm$ 0.07  &1d   &2--10
  &26.70 & gb05\\ 
990123 &1.60  &1.35         &0.99 $\pm$ 0.07 &5.3 $\pm$ 0.2    &11h &1.6--10
  &27.69& dp03, he99 \\  
       &      &1.44 $\pm$ 0.11 &1.00 $\pm$ 0.05 &1.8 $\pm$ 0.4    &1d   &2--10
       & 27.72 &gb05 \\  
990510 &1.619 &1.4 $\pm$ 0.1   &1.2 $\pm$ 0.2   &1.2 $\pm$ 0.2    &1d   &2--10
  &27.57 & gb05\\  
991216 &1.02  &1.6 $\pm$ 0.1   &1.2 $\pm$ 0.2   &2.58          &37h &2--10
  &27.77 & pi00 \\
  &      &      1.6 $\pm$ 0.1 &0.8 $\pm$ 0.5   &5.6 $\pm$ 0.3    &1d   &2--10
  &27.89 & gb05 \\ 
\object{000210} &0.846$^2$ &1.38 $\pm$ 0.03 &0.95 $\pm$ 0.15 &0.4 $\pm$ 0.06   &11h &2--10
       &26.13 & pi02 \\ 
       &      &1.38 $\pm$ 0.03 &0.9 $\pm$ 0.2   &0.21 $\pm$ 0.06  &1d   &2--10
       &26.32 & gb05 \\ 
\object{000214} & 0.42$^3$ &0.8 $\pm$ 0.5$^b$ &1.2 $\pm$ 0.3 &0.77 $\pm$ 0.08  &15h &2--10
        &26.01 & an00\\ 
       &      &0.7 $\pm$ 0.3   &1.2 $\pm$ 0.5   &0.6 $\pm$ 0.2    &1d   &2--10
    &26.05 & gb05\\  
000926 &2.066 &1.7 $\pm$ 0.5   &0.7 $\pm$ 0.2   &0.12 $\pm$ 0.1   &2.78d &2--10
   &27.35 & gb05\\   
010222 &1.477 &1.33 $\pm$ 0.04 &1.01 $\pm$ 0.06 &2.7 $\pm$ 0.6    &1d   &2--10
   &27.85 & gb05 \\  
011121 &0.36  &$4^{+3}_{-2}$&2.4 $\pm$ 0.4   &0.6 $\pm$ 0.2    &1d   &2--10
  &26.11 & gb05 \\ 
011211 &2.14  &1.3 $\pm$ 0.1  &1.2 $\pm$ 0.1    &0.03 $\pm$ 0.01  &1d   &2--10
  &26.19 & gb05 \\ 
020405 &0.69  &1.9 $\pm$ 1.1  &0.72 $\pm$ 0.21  &1.36 $\pm$ 0.25  &1.71d
  &0.2--10 &27.21 & mi03\\   
020813 &1.25  &1.38 $\pm$ 0.06&0.85 $\pm$ 0.04  &2.2           &1.33d
  &0.6--6 &27.70 & bu03 \\  
021004 &2.33  &0.9 $\pm$ 0.1  &1.01 $\pm$ 0.08  &0.63          & 1.37d
  &0.6--6 &27.60 & but03 \\  
030226 &1.98  &2.7 $\pm$ 1.6  &0.9 $\pm$ 0.2    &0.035 $\pm$ 0.002&1.77d &2--10
  &26.59 & gb05\\ 
030329 &0.168 &0.9 $\pm$ 0.3  &0.9 $\pm$ 0.2    &14.3 $\pm$ 2.9   &1d   &2--10
  &26.69 & gb05  \\ 
\hline 
\end{tabular}}
\medskip
$^a$ 970508 showed a substantial rebrightening, correlated
with the optical (Piro et~al. \cite{Piro98}); $^b$ decay index considering only
MECS~data. If WFC is included, $\alpha=1.41$~$\pm$ $0.03$ (Antonelli et~al. \cite{Antone00}).  For GRB~030329 we have calculated the X-ray flux at~12~h
rest frame extrapolating from earlier data, since this GRBs showed a~jet
break at approximately 10~h (rest frame time) (see Tiengo et~al. \cite{Tien04}).
References: 
co97: Costa et~al. (\cite{Cost97}); 
gb05: Gendre \& Bo\"er (\cite{Gendr05}); 
pi98: Piro et~al. (\cite{Piro98}); st04: 
Stratta et~al. (\cite{Strat04}); 
co99: Costa et~al. (1999); 
dp03: De~Pasquale et~al. (\cite{DePas03}); 
he99: Heise et~al. (\cite{Heis99}); 
pi00: Piro et~al. (\cite{Piro00}); 
pi02: Piro et~al. (\cite{Piro02}); 
an00: Antonelli et~al. (\cite{Antone00}); 
mi03: Mirabal et~al. (\cite{Mirab03}); 
bu03: Butler et~al. (\cite{Butl03}).
$^1$ Djorgovski et~al. (\cite{Djorgo99});   
$^2$ Piro et~al. (\cite{Piro02});
$^3$ Antonelli et~al. (\cite{Antone00}).
\end{table}