[vsnet-grb-info 2786] GRB 051211A: MDM Observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4623
SUBJECT: GRB 051211A: MDM Observations
DATE:    06/01/31 00:15:50 GMT
FROM:    Jules Halpern at Columbia U.  <jules at astro.columbia.edu>

J. P. Halpern (Columbia U.) & N. Mirabal (U. Michigan) report on behalf 
of the MDM Observatory GRB follow-up team:

"Guidorzi et al. (GCN 4356) reported a possible optical afterglow 
for the HETE-2 burst GRB 051211A (Atteia et al., GCN 4324; Kawai
et al., GCN 4359) that faded from R = 21.15+/-0.15 to R = 21.75+/-0.20
between 6.3 hr and 11.4 hr after the burst.  As they noted that there
is a hint of its presence on the I-band POSS plate, and in view of
the likelihood that this was a short burst (Norris et al., GCN 4377),
it is interesting to follow up on this candidate afterglow to determine
if it is hosted by a relatively nearby galaxy.  We observed and detected
the same object on 2005 Dec. 25 with the MDM 2.4m telescope and RETROCAM
imager in five 300 s exposures in the SDSS r' filter.  Its position is
R.A. = 06:56:09.00, Decl. = +32:40:06.3 (J2000), the same as previously
determined.  Calibration with Landolt stars yields R = 21.72+/-0.05
(statistical), with an additional systematic uncertainty of 0.1 likely.
This is consistent with the later measurement of Guidorzi et al.,
but not their earlier one.  The object is not resolved in our images
at the seeing of 0.95", which argues against a host interpretation.
We observed it again in the I band with the MDM 8K imager on 2006 Jan. 29.
Three 600 s exposures were obtained in seeing of 0.85".  Although the
latter images are uncalibrated, the object appears not to have faded,
is still at the limit of the I-band POSS plate, and is still unresolved.
Therefore, we conclude that it is most likely a star and not the
afterglow of GRB 051211A.

The MDM I-band image is posted at 

http://www.astro.columbia.edu/~jules/grb/051211a/

This message may be cited"