\begin{table}%t3
\caption{\label{table:SA_SF}Analysis of the structure function in the hard X-ray band.}            
%\centering
\par
\begin{tabular}{c c c c}       
\hline\hline                 
Obs.   & Start lag & End lag & $H$  \\    
period & [s]       & [s]     &      \\    
\hline  \noalign{\smallskip}                      
OB1 & $10^{4.9}$ & $10^6$     & 0.185 \\
OB2 & $10^{3.9}$ & $10^{5.2}$ & 0.147 \\
OB3 & $10^{3.9}$ & $10^{4.9}$ & 0.115 \\
    & $10^{5.2}$ & $10^{5.6}$ & 0.210 \\
OB4 & $10^{4.9}$ & $10^{5.7}$ & 0.170 \\
\hline                                  
\end{tabular}
\end{table}