\begin{table}%t3
\caption{\label{tab:properties}Basic properties of Sharov~21 (remarks: see text).}
\begin{tabular}{lll}
\hline\hline\noalign{\smallskip}
\multicolumn{2}{l}{Measured and derived quantities}       & Remark\\
\hline\noalign{\smallskip}
RA (2000)                           & $00^{\rm h}44^{\rm m}57\fs94$ &(1)\\
Dec (2000)                          & $+41\degr23\arcmin43\farcs$9  &(1)\\
redshift $z$                        & 2.109               &\\
projected distance from M~31 centre  & 26\arcmin           &\\
apparent magnitude $B$              & 20.5/17.2           &(2)\\
foreground dust reddening $E(B-V)$  & 0.2 mag             &\\        
absolute magnitude $M_{\rm B}$      & $-27.5/\!\!-30.7$       &(2)\\
date of the maximum (year/JD)       & 1992.81/2448918     &\\
$t_{1/2}$ decline (days)            & 15/5                &(3)\\
black hole mass $M_{\rm bh}$        & $5\times10^8~M_\odot$  &(4)\\
$\log~(L_{\rm bol}/$ erg\ s$^{-1}$)& 46.6               &(5)\\
Eddington ratio $L_{\rm bol}/L_{\rm edd}$ & 0.60          &(5)\\
\hline
&\\
\end{tabular}
\end{table}