GCN Circular 666

[WARNING: This is not a typical GCN reporting observations associated
with any GRB detection. The uniqueness of this transient object (see
below) and its remote chance of being GRB-related along with its rapid 
fading prompt this GCN.]

R. Hudec, V. Simon (Astronomical Institute Ondrejov), M. Tichy and 
J. Ticha (Klet Observatory), W. Li, A. Filippenko and M. Papenkova (UCB), 
F. Vrba and B. Canzian (USNO Flagstaff) report:

We have obtained seven CCD observations with the 0.8 automatic KAIT,
0.6 m Klet, and 1.0 m Flagstaff telescopes covering the position of the 
optical transient detected in the field of NGC 3432 (IAUC 7415: 
R.A. 10h 52m41.40s, Decl. +36o40'08.5", equinox 2000.0). The object is 
about 123" east and 180" north of the diffuse nucleus and superimposed 
on an HII region (or the spiral arm) of this interacting dwarf galaxy 
at D = 7.8 Mpc.

The object was discovered on May 3.228 UT at nearly mag 17.4 (unfiltered 
image) and since then (our last measurement is from May 9.181 UT) has 
faded by nearly 3.5 magnitudes, similar to rapid GRB optical afterglow
declines. Analysis of the data taken at our observatories is in 
progress to produce a final light curve. Preliminary analysis indicates 
that a power law fits the data well with a slope of -3.3 +/- 0.1, if T_0 
is assumed to be May 0.0 UT for instance, (based on differential photometry 
with respect only to a nearby star so far), although without a known GRB time
the choice of this T_0 is totally arbitrary.

A spectrum of the object (IAUC 7417) shows its distance to be consistent 
with that of NGC 3432 and thus not a foreground or background object. 
While this spectrum is consistent with that of a classical nova, the 
the brightness at this distance would make the nova extraordinarily
bright. The object might yet be a (probably absorbed) optical afterglow 
of a not-observed GRB (due to different beaming opening angles in gamma 
rays and in the optical). Even if this not a GRB optical afterglow (an 
extraordinary bright nova, for instance ), the object is still worthy of 
further study, but is rapidly fading into the background of NGC 3432.
Tonight might be the last opportunity to observe it.

The discovery FITS frame is available by anonymous ftp at flipper.berkeley.edu,
in the directory /pub/bait/ngc3432. Finding charts from UT May 07 and
09 showing the object fading are avaiable in postscript format by anonymous 
ftp at ftp.nofs.navy.mil in the directory /pub/outgoing/fjv/ngc3432.dir.