TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2964
SUBJECT: Unusual optical transient (GRB ???)
DATE:    05/01/19 17:12:22 GMT
FROM:    Jean-Luc Atteia at Lab d Astrophys.,OMP,Toulouse  <atteia@ast.obs-mip.fr>

Subject: Unusual optical transient (GRB ???)

F. Malacrino, JL. Atteia (LA-OMP), M. Boer (OHP), A. Klotz (CESR-OMP),
C. Veillet, J-C. Cuillandre (CFHT), JJ. Kaavelars (HIA-NRC)
report on behalf of the GRB Real Time Analysis System at CFHT.

We observed an unusual optical transient recorded within the course of
the Very-Wide Survey of the CFHTLS ( http://www.cfht.hawaii.edu/Science/CFHLS/ ).
The transient is seen on January 16, 2005 in a series of three consecutive
exposures with the following relative g’ magnitudes (accurate to ~0.5 mag):

16-01-2005, 29408s, g’= 20.5 ± 0.1
16-01-2005, 33036s, g’= 22.1 ± 0.1
16-01-2005, 36299s, g’= 23.0 ± 0.5

On January 17th the transient is not detected down to g’~23.5

The coordinates (J2000) of the transient are:

RA = 08 43 55.21 ± 2”
DEC = 20 02 22.2 ± 2”

We have no color information on the transient, and there is no object in
the USNO-B1 Catalog (Monet 2003) at this position.

Given the fast decay of the source we consider that it is more likely to be
a faint flare star (like the transient reported in GCNs 2849, 2850, 2851)
rather than a GRB afterglow .
We nevertheless communicate the position of this transient to the community
of GRB observers in case there is some opportunity for follow-up at radio or
optical wavelengths with large instruments.