\begin{table}
%\centering
\par
\caption{Low energy limiting photon spectral index $\alpha$
[i.e. $N(E) \propto E^\alpha$] for various emission models.  For
clarity the indices for the energy spectrum $F(E)$ and for its
$E F_{E}$ representation are also reported.  }
\label{alfa_models}
\begin{tabular}{cccl}
\hline
\hline
% \noalign{\smallskip}
$\alpha$  & $\alpha+1$ & $\alpha+2$ & \\
% \hline 
% \noalign{\smallskip}
$N(E)$ & $F(E)$ & $EF_{E}$ & model/spectrum \\
% $$\mathrm{\frac{phot}{cm^{2}\           s\          keV}}$$          &
% $$\mathrm{\frac{keV}{cm^{2}\  s}}$$  & $$\mathrm{keV(\frac{keV}{cm^{2}
% s})}$$  & model  \\  
% \noalign{\smallskip} 
\hline  
% \noalign{\smallskip}
$-$3/2 & $-$1/2 & 1/2 &  Synchrotron emission with cooling \\  
$-$1   &  0   &  1  & Quasi--saturated Comptonization \\
$-$2/3 & 1/3  & 4/3 & Instantaneous synchrotron \\ 
0    & 1    & 2   & Small pitch\ angle/jitter\\
     &      &     & Inverse Compton by\ single e$^{-}$  \\ 
1    & 2    & 3   & Black Body \\  
2    &  3   & 4   & Wien  \\
% \noalign{\smallskip} 
\hline 
\end{tabular}
\end{table}