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\IBVShead{5737}{27 November 2006}

\IBVStitletl{The Optical Counterpart of the Possible}{ Brightest Transient X-ray Source in M31 is Found}

\IBVSauth{Smirnova, O.$^1$; Alksnis, A.$^1$; Zharova, A.V.$^2$}

\IBVSinst{Institute of Astronomy, University of Latvia, Raina
bulv.\ 19, Riga LV-1586, Latvia;\\ \indent e-mail: o.smirnova@inbox.lv}

\IBVSinst{Sternberg Astronomical Institute, University of Moscow,
13, University Ave., Moscow 119992, Russia}

\IBVStyp{ Nova }

\IBVSkey{photometry}

\IBVSabs{On the Baldone Schmidt telescope plates taken in}
\IBVSabs{November 2001 an apparent nova in M31 - an optical}
\IBVSabs{counterpart of the supersoft X-ray source n1-86 was}
\IBVSabs{found.}

\begintext

Having found a nova in M31 on plates of the Baldone Schmidt
telescope plate archive (Smirnova \& Alksnis, 2006), which
occurred to be the optical counterpart of the supersoft X-ray
source [PFH2005]~191 (Pietsch et al., 2005a), we started to
inspect the positions of known M31 supersoft X-ray sources on
scans of other plates of M31 taken in the years 2001-2002.

An object was found at the position of the supersoft X-ray source
[PFH2005]~543 (Pietsch et al., 2005a) on the plate No.~248 taken
on November 12, 2001. Its coordinates R.A. = 00\hr44\mm14\fsec52,
Decl. = +41\deg22\arcm4\farcs3\ (equinox~2000.0; estimated maximal
 error radius 0\farcs7) determined from the scanned discovery
plate, on which the nova is the brightest, with respect to the
positions of field stars from UCAC2, agree with those of the
[PFH2005]~543 within 0\farcs5. So it is highly probable that the
newly found object is the optical counterpart of the X-ray source
[PFH2005]~543.

The X-ray source, designated as XMMU~J004414.0+412204, was
discovered on January 5, 2002 by Trudolyubov et al.\ (2002),
confirmed on January 8, 2002 by Garcia et al.\ (2002), observed on
highest luminosity level on February 6, 2002 and included in the
catalog of transient X-ray sources in M31 (Williams et al., 2006)
as object n1-86. Williams et al.\ (2006) did not exclude the
possibility that the X-ray source n1-86 is in M31 and might have
the highest X-ray luminosity of any transients yet observed in
M31. Trudolyubov et al.\ (2005) did not succeed in search for
optical counterparts of the X-ray source, but according to them
the transient behavior of the source hints that it may be a
classical nova in supersoft X-ray spectral phase.

A finding chart of the nova from the discovery plate is given in
Figure~1. Times of the middle of exposures in Julian days and blue
magnitudes ($m_B$) of the nova based on the secondary standard
stars from the $BVRI$ catalogue of M31 (Magnier et al., 1992) are
given in Table~1. The light curve of the nova is presented in
Figure~2.

The object was first observed when it was near the outburst
maximum, which evidently occurred within a day before or after our
first observation. The estimated light decay rate $dB/dt>0.2$ m/d
during observation period suggests that probably the nova was very
fast. Thus according to our observations the photometric behavior
of the object seems to be typical for novae in M31.

\begin{table}[h]
\begin{center}
{\normalsize Table 1}\\
\smallskip
\begin{tabular}{cr@{.}l}
\hline
   JD          &  \multicolumn{2}{c}{$m_B$}    \\
2452200 +      &    \multicolumn{2}{c}{mag} \\
\hline
            25.216        & $>19$&1 \\
            26.208        &   17&1 \\
            28.238        &   18&2 \\
            33.327        &   19&3: \\
            34.292        &   19&2 \\
            48.188        & $>19$&4 \\
\hline
\end{tabular}
\end{center}
\end{table}


\IBVSfig{8cm}{5737-f1.ps}{Finding chart for the
discovered nova. The cross shows the position of the X-ray source
[PFH2005]~543}
\IBVSfigKey{5737-f1.ps}{[PFH2005] 543}{finding chart}

\IBVSfig{9cm}{5737-f2.ps}{The light curve of the
nova in M31. Filled circles: confident measurements; open circle:
uncertain measurement; triangles:  brightness upper limits}
\IBVSfigKey{5737-f2.ps}{[PFH2005] 543}{light curve}

Possibly because of its high X-ray luminosity the nova is
also unique in another aspect: the time separation between its
optical outburst and detection as supersoft X-ray source is the
shortest known for novae in M31 --- only 53 days, followed by
WeCaPP-N2001-12 with 63 days (Pietsch et al., 2005b) and the
optical counterpart of the X-ray source [PFH2005]~191 with 84 days
(Smirnova \& Alksnis, 2006).

\vspace{12pt}

{\bf Corrigendum.} In the paper by Smirnova \& Alksnis (2006), third
paragraph from the end, instead of 1/10/2001 should be 1/10/1992.
Our thanks are due to W. Pietsch for pointing out this error.

\references

Garcia, M.R., Kong, A.H.K., McClintock, J.E., Primini, F.A.,
Kaaret, P., Murray, S.S., 2002, {\it The Astronomer's Telegram},
No.\ 82 %\BIBCODE{2002ATel...82....1G}

Magnier, E.A., Lewin, W.H.G., van Paradijs, J., Hasinger, G.,
Jain, A., Pietsch, W., Truemper, J., 1992, {\it A\&AS}, {\bf 96},
379 %\BIBCODE{1992A&AS...96..379M}

Pietsch, W., Freyberg, M., Haberl, F., 2005a, {\it A\&A}, {\bf
434}, 483 %\BIBCODE{2005A&A...434..483P}

Pietsch, W., Fliri, J., Freyberg, M.J., Greiner, J., Haberl, F.,
Riffeser A., Sala, G., 2005b, {\it A\&A}, {\bf 442}, 879
%\BIBCODE{2005A&A...442..879P}

Smirnova, O., Alksnis, A., 2006, {\it IBVS}, No.\ 5720
%\BIBCODE{2006IBVS.5720....1S}

Trudolyubov, S., Kotov, O., Priedhorsky, W., Cordova, F., Mason,
K., 2005, {\it ApJ}, {\bf 634}, 314 

Trudolyubov, S., Priedhorsky, W., Borozdin, K., Mason, K.,
Cordova, F., 2002, {\it IAUC}, No.\ 7798
%\BIBCODE{2002IAUC.7798....2T}

Williams, B.F., Naik, S., Garcia, M.R., Callanan, P.J., 2006, {\it
ApJ}, {\bf 643}, 356 %\BIBCODE{2006ApJ...643..356W}

\endreferences

\end{document}
