\begin{table}%T2
\caption{Best-fit parameters for the X-ray spectra of 4U~1954+31 from
the pointed observations described in this paper. In all models in which a
Fe~emission line is needed in the fit, its width is fixed at the value
$\sigma = 0.1$~keV. Frozen parameters are written between square
brackets. Luminosities are not corrected for the intervening absorptions 
and are computed assuming a distance $d$ = 1.7 kpc (Masetti et~al. \cite{Masetti06a}); 
in the cases in which the X-ray data could not completely cover the 
X-ray interval of interest for the luminosity determination, an 
extrapolation of the best-fit model is applied. Errors are at 90\% 
confidence level for a single parameter of interest. Observations are 
reported in chronological order from left to right.}\label{t2}
%\centerline
 {\small
\begin{tabular}{ccccccc}
\hline
\hline
\noalign{\smallskip}
\multicolumn{7}{c}{model: {\sc wabs*[pcfabs*wndabs(comptt + gauss) + mekal]}} \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
Parameters$^{a}$ & {\it EXOSAT}~I & {\it EXOSAT}~II & {\it ROSAT} & {\it RXTE} & {\it BeppoSAX} & 
{\it Swift} \\
 & (1$-$15~keV) & (1$-$15~keV) & (0.1$-$2~keV) & (2.5$-$100~keV) & (0.2$-$150~keV) & 
(1.8$-$8.5~keV) \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
${\chi^{2}}$/d.o.f.         & 217.7/204 & 86.0/85 & 20.0/18 & 112.6/105 & 280.1/247 & 53.4/44 \\
\noalign{\smallskip}
$N_{\rm H}^{\rm WABS}$   & [1.5] & [1.5] & [1.5] & [1.5] & 1.5$^{+0.6}_{-0.4}$ & [1.5] \\[1mm]
$N_{\rm H}^{\rm PCFABS}$ & --- & --- & [25.4] & --- & 25.4 $\pm$ 1.6 & 1.4$^{+2.6}_{-1.2}$ \\[1mm]
$C_{\rm PCFABS}$ (\%)    & --- & --- & [95] & --- & 95 $\pm$ 2 & [95] \\
$N_{\rm H}^{\rm WNDABS}$ & --- & --- & [3.0] & 4.1$^{+0.2}_{-0.3}$ & 3.0$^{+1.3}_{-0.7}$ & --- \\[1mm]
$E_{\rm WNDABS}$ (keV)   & --- & --- & [1.86] & [1.86] & 1.86$^{+0.10}_{-0.13}$ & --- \\[1mm]
$kT_0$ (keV)             & 0.56 $\pm$ 0.04 & 0.94$^{+0.05}_{-0.06}$ & [1.28] & 
1.156$^{+0.017}_{-0.009}$ & 1.28 $\pm$ 0.06 & 0.6$^{+0.4}_{-0.6}$ \\[1mm]
$kT_{\rm e^{-}}$ (keV)   & 2.86$^{+0.12}_{-0.10}$ & 13$^{+\infty}_{-9}$ & [9.9] & 13$^{+14}_{-3}$ & 
9.9 $\pm$ 0.8 & 8$^{+\infty}_{-2}$ \\[1mm]
$\tau$                   & 9.4$^{+0.5}_{-0.4}$ & 3.2$^{+2.5}_{-3.2}$ & [2.8] & 2.0$^{+0.5}_{-0.4}$ & 
2.8$^{+0.3}_{-0.2}$ & 4$^{+5}_{-4}$ \\[1mm]
$K_{\rm COMPTT}$ ($\times 10^{-3}$) & 50$^{+2}_{-3}$ & 2.1$^{+3.6}_{-2.1}$ & [8.2] & 
5.0$^{+0.4}_{-2.4}$ & 8.2 $\pm$ 0.8 & 6$^{+120}_{-6}$ \\
$kT_{\rm MEKAL}$ ($\times 10^{-2}$~keV) & --- & --- & 5.3$^{+1.5}_{-1.2}$ & --- & 6.8$^{+2.2}_{-1.5}$ & --- \\[1mm]
$K_{\rm MEKAL}$          & --- & --- & 300$^{+5600}_{-290}$ & --- & 200$^{+5400}_{-190}$ & --- \\[1mm]
$E_{\rm Fe}$ (keV)       & --- & --- & N/A & 6.46$^{+0.12}_{-0.11}$ & 6.46$^{+0.10}_{-0.11}$ & --- \\[1mm]
$I_{\rm Fe}$ ($\times 10^{-4}$ ph cm$^{-2}$ s$^{-1}$) & --- & --- & N/A & 1.9$^{+0.5}_{-0.4}$ & 
2.5 $\pm$ 1.0 & --- \\
\noalign{\smallskip}
\hline%\\[-3.2mm]
\noalign{\smallskip}
\multicolumn{1}{l}{X-ray luminosities$^{b}$:} & & & & & & \\
0.1$-$2~keV  & --- & --- & 4.1 $\times$ 10$^{31}$ & --- & 2.0 $\times$ 10$^{32}$ & --- \\
2$-$10~keV   & 1.8 $\times$ 10$^{35}$ & 3.4 $\times$ 10$^{34}$ & --- & 7.9 $\times$ 10$^{34}$ & 
5.2 $\times$ 10$^{34}$ & 5.2 $\times$ 10$^{34}$ \\
10$-$100~keV  & --- & --- & --- & 1.2 $\times$ 10$^{35}$ & 1.8 $\times$ 10$^{35}$ & --- \\
%\noalign{\smallskip}
\hline
\end{tabular}}
\medskip
\par
$^{a}$ Hydrogen column densities are in units of 10$^{22}$ cm$^{-2}$.  \\
$^{b}$ In units of erg s$^{-1}$. Values are not corrected for absorption. 
N/A: not applicable because of lack of spectral coverage.
\end{table}