[vsnet-grb-info 2519] GRB051211A: possible optical candidate

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4356
SUBJECT: GRB051211A: possible optical candidate
DATE:    05/12/15 14:13:31 GMT
FROM:    Cristiano Guidorzi at ARI,Liverpool JMU  <crg at astro.livjm.ac.uk>

C. Guidorzi, A. Monfardini, I.A. Steele, A. Gomboc, C.G. Mundell,
C.J. Mottram, R.J. Smith, D. Bersier, A. Melandri, S. Kobayashi, 
D. Carter, M.F. Bode (Liverpool JMU), N. Tanvir (Hertfordshire)
report:


"The 2-m Faulkes Telescope North observed GRB051211A discovered by
HETE-2 (Atteia et al, GCN 4324) from 5.9 to 11.9 hours after the
burst.
So far, searches for afterglow have provided just upper limits in the
optical (de Ugarte Postigo et al. GCN 4325 & GCN 4335, Klotz et al. GCN
4329, Jelinek et al. GCN 4333, Maeno et al. GCN 4339, Blustin et al. GCN
4342, Zhuchkov et al. GCN 4344) as well as in the X-rays (Cusumano et al.
GCN 4326).
>From the comparison of two 30-min stacked images, we found an object at
RA=06:56:09.0, DEC= +32:40:06.4 (J2000) showing some evidence of a fading
of 0.6 +- 0.3 mag (calibrated with USNOB stars of the field, with an
uncertainty of 0.4 mag affecting just the absolute values, but not the
relative ones). It lies 63 arcsec away from the HETE-2 centroid (given
with an error radius of 80 arcsec at 90% CL).

-----------------------------------------------------
Start Time	Filter	Exposure	Mag
since GRB
 
 6.3 hr		R	12x150s		21.15 +- 0.15
11.4 hr		R	12x150s		21.75 +- 0.20
-----------------------------------------------------
 
This candidate does not match any DSS source, although we notice a small
blur in the DSS IR that might be either a faint source or a background
fluctuation.
If we assume the fading is genuine, the average temporal decay
power-law index turns out to be around 1.0 +- 0.5.
However, a word of caution is required, as the source magnitude is
close to the limiting value affected by the moonlight.
 
An image of the OT candidate at both epochs is available at the following:
 
http://www.astro.livjm.ac.uk/~crg/GRB051211A_possible_OT_FTN.jpg
 
We encourage further observations."