\begin{table}%t1
\caption{The astronomical databases used to build the reference catalogue. Database acronyms, objects class and the references for each catalogue are shown from left to right. GC and GP are the Galactic Center and Plane.}\label{Cats}
%\centering
\par
\begin{tabular}{ccc}
\hline \hline
Database name & Objects class & References  \\
\hline
 XRB & X-ray binary systems & \citet{XRB}   \\
 HMXRB & High mass X-ray binary systems &  \citet{HMXB}     \\
 LMXRB & Low mass X-ray binary systems & \citet{LMXB}    \\
 INTEGRAL-IBIS GP soft $\gamma$-ray catalogue & X-ray binary systems &\citet{INTS}    \\
  INTEGRAL-IBIS hard X-ray GC survey  &  & \citet{INTH}  \\
 Swift-BAT high galactic latitude survey & AGN & \citet{BAT}   \\
 ZCAT  & galaxies with \textit{B} magnitude $<$14 & \citet{Zcat}   \\
 AGN  & Active galactic nuclei & \citet{Pad97}  and   \\
& & private communication    \\
RASS-BSC   & ROSAT all-sky survey bright sources & \citet{Vog99}    \\
& with 0.1--2.4~keV flux $>$~10$^{-11}$~{\rm erg s}$^{-1}$~{\rm cm}$^{-2}$ &     \\
 Sedentary   &  high energy peaked BL LACs (HBL) &  \citet{Gio99}, \citet{Gio05}   \\
 CABSCAT     & Spectroscopic binary systems &  \citet{Str88}, \citet{Str93}   \\
 CVCAT       & Cataclismic variable stars &  \citet{CVcat}     \\
 ALLWARPS    & Cluster of galaxies &  \citet{AllWarps}  \\
 BASSANI     & Absorbed active galactic nuclei & private communication   \\
\hline
\end{tabular}
\end{table}