\begin{table}%t1
\caption{\label{tab:previous_obs}Summary of previous observations of the spectral index $\alpha_\nu$ of the Crab pulsar.}
%\centering
\par
\begin{tabular}{c c c}
\hline\hline
\noalign{\smallskip}
Reference & $\alpha_\nu$ & $\lambda$-range ($\AA$) \\
\hline 
\cite{nasuti96}	& $-0.10\pm0.01$	& $4900{-}7000$  \\ 
\cite{carraminana00} & $0.2\pm0.1$		& $5000{-}7500$  \\
\cite{sollerman00}	& $0.11\pm0.04$		& $1140{-}9250$  \\ 
\cite{beskin01}		& $-0.15\pm0.15$	& $5000{-}7050$   \\ 
\cite{fordham02}	& $-0.034\pm0.009$ & $4600{-}6000$  \\
\hline
\cite{percival93} 	& $0.11\pm0.13$ 	& $1680{-}7400$  \\ 
\cite{golden00b}	& $-0.07\pm0.19$	& $3700{-}5500$   \\ 
\cite{sollerman03} & $0.31\pm0.02$ & $12~400{-}21~800$  \\
\cite{ss09} 		& $0.27\pm0.03$ & $3700{-}38~000$ \\
\hline
\end{tabular} 
\end{table}