\begin{table}%t4
\caption{Observed mean and maximum radio flux densities and estimated distances for the six~Z~sources and GX~13+1. This table is reproduced from Tables~\ref{tab_spectra} and~\ref{tab_pds} in \citet{fehe2000}, with updated values for GX~13+1.}\label{tab:radio}
%\centerline
{
\begin{tabular}{lcccc}
\hline  \hline
Source & Mean$^a$        & Max$^b$      & distance & Refs\\
       & (mJy)           &  (mJy)       & (kpc)    & \\
\hline
Sco X-1  & $10 \pm 3$    & 22 & $2.0 \pm 1.0$ & 1, 2 \\
GX 17+2  & $1.0 \pm 0.3$ & 13.4 & $7.5 \pm 2.3$ & 1, 3\\
GX 349+2 & $0.6 \pm 0.3$ & 1.3 & $5.0 \pm 1.5$ & 4, 5\\
Cyg X-2  & $0.6 \pm 0.2$ & 3.4 & $8.0 \pm 2.4$ & 1, 6, 7\\
GX 5-1   & $1.3 \pm 0.3$ & 1.6 & $9.2 \pm 2.7$ & 1\\
GX 340+0 & $0.6 \pm 0.3$ & 0.6 & $11.0 \pm 3.3$ & 8\\
GX 13+1  & $1.8 \pm 0.3$ & 7.7 & $7 \pm 1$ & 9--13 \\
\hline
\end{tabular}}
\medskip
$^a$ Mean cm radio flux density.\\
$^b$ Maximum radio flux density at 6 cm. \\
Refs. 1: \citet{pe1989};
2: \citet{brfoge1999};
3: \citet{pelezi1988};
4: \citet{copo1991};
5: \citet{chsw1997};
6:~\citet{hjhaco1990};
7: \citet{cocrhu1979};
8:~\citet{pezwva1993};
9: \citet{grse1986};
10: \citet{gagrmo1988};
11:~\citet{befeku1999};
12: \citet{bashch1999};
13: this work.
\end{table}