[vsnet-grb-info 2555] GRB 051221A: MDM Optical Observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4392
SUBJECT: GRB 051221A: MDM Optical Observations
DATE:    05/12/23 23:04:14 GMT
FROM:    Markus Boettcher at Ohio U  <mboett at helios.phy.ohiou.edu>

M. Boettcher and M. Joshi (Ohio University) report:

Starting on 21 Dec., UT 04:02, we observed the optical
afterglow of GRB 051221A (Parsons et al. GCN 4363) with
the MDM 1.3 m telescope in three 600 s exposures (beginning
2.1, 2.4, and 2.6 hr after the trigger). We detect a faint
source consistent with the locations of the IR (Bloom,
GCN 4367 and 4368), optical (Berger, GCN 4369, 4371;
Berger and Soderberg, GCN 4375; Berger et al. GCN 4383),
and X-ray (Burrows et al., GCN 4366; Grupe et al. GCN 4389)
afterglows. Photometry, calibrated on the R-band magnitudes
of 6 comparison stars in our field of view as given by
Aladin, from the UCD data base (UCD: PHOT_PHG_R), yields
the following magnitude estimates (t = time after GRB trigger):

 t          |     R
-------------------
2.1 hr   |  19.88 +/- 0.40
2.4 hr   |  19.93 +/- 0.39
2.6 hr   |  19.98 +/- 0.34

Consequently, there is no evidence for variability between
the three frames. Seeing was rather poor (~ 2 arc sec.), so
the optical afterglow is not resolved from the host galaxy
(Soderberg and Berger, GCN 4375). Given the RAPTOR upper
limit on the fading counterpart of R > 20.2 at 1.3 hr
after the trigger (Wren et al., GCN 4380), our measurement
might in fact be dominated by the host galaxy contribution.

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