[vsnet-grb-info 2868] Orphan GRB Afterglow candidate

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4705
SUBJECT: Orphan GRB Afterglow candidate
DATE:    06/02/07 15:55:09 GMT
FROM:    Jean-Luc Atteia at Lab d Astrophys.,OMP,Toulouse  <atteia at ast.obs-mip.fr>

F. Malacrino & JL. Atteia (LA-OMP) report on behalf of the GRB Real Time
Analysis System at CFHT (http://www.cfht.hawaii.edu/~grb/).

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/ ).

We consider that this transient is a possible GRB afterglow.

The transient is stationary and detected in a series of three consecutive
180s long i' band exposures taken on the night of February 2nd, 2006.
The transient is not seen in a 180s long i' band exposure taken
on the following night.

The magnitudes of the transient are :

02-02-2006, 26797s, i’= 20.8 ± 0.2
02-02-2006, 30060s, i’= 20.7 ± 0.2
02-02-2006, 33207s, i’= 20.6 ± 0.2

03-02-2006, 27802s, i' > 23.0


The coordinates (J2000) of the transient are:

RA = 05 07 33.83 ± 0.5"
DEC = +22 17 10.9 ± 0.5”

A finding chart can be found at the following address:
http://www.cfht.hawaii.edu/~grb/double/06AQ01/836441o836294o/glo.html#N03CCD26
the transient is seen in the leftmost image.

We have no color information on the transient.


We have perfomed the following verifications to check the possible nature
of this object:

- There is no object in the USNO-B1 Catalog (Monet 2003) at this position.

- There is no object at this position in all the VizieR catalogs
    (http://vizier.u-strasbg.fr/viz-bin/VizieR)

- There is no object at this position in the DSS or 2MASS images.

- There is no detectable source at this position in archival images
    taken at the CFHT in g' band (there are no archival images in the i'
band).


To date, after 1.5 years of operation, this object is our best candidate
for a GRB afterglow. If this is truly a GRB afterglow, we note that
the fast decrease of the source between the nights of February 2nd and 3rd
implies that we have caught the afterglow a few hours only after the GRB.

We strongly encourage follow-up observations at all wavelengths,
especially in X-rays and radio given the age of the afterglow (5 days),
and also in IR since the source was detected in the i' band.