[vsnet-grb-info 7055] GRB 081128: afterglow observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8639
SUBJECT: GRB 081128: afterglow observations
DATE:    08/12/08 08:35:39 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at astro.ku.dk>

D. Malesani, J.P.U. Fynbo, G. Leloudas (DARK/NBI), H. Pedersen (NBI), P. 
Jakobsson (Univ. Iceland), S.-M. Niemi, H. Uthas, and C. Villforth 
(NOT), report on behalf of a larger collaboration:

We observed the field of GRB 081128 (Margutti et al., GCN 8571) with the 
Nordic Optical Telescope equipped with ALFOSC. Observations were carried 
out on two epochs, first on 2008 Nov 28.962 (0.24 days after the GRB) in 
the V, R and i bands and then on Dec 7.827 (9.10 days after the GRB) in 
the R band. In the first epoch we detect the afterglow candidate 
reported by Wang et al. (GCN 8572) in all filters. We estimate R=22.3 +- 
0.1 assuming R=17.91 for the USNO star at RA = 01:23:11.73, Dec = 
+38:07:43.58 (consistent with the calibration of Guidorzi et al., GCN 
8577; C. Guidorzi, priv. comm.). In the second epoch, the afterglow 
candidate remains undetected to a limit R > 23.5, and we hence confirm 
that this source is the GRB afterglow. We note that the V-band detection 
sets a limit on the GRB redshift, z <~ 5.

We also detect in both epochs a second object at the border of the XRT 
error circle (RA = 01:23:12.98, Dec = +38:07:38.4), which is likely the 
one reported by Guidorzi et al. (GCN 8577), with a magnitude R = 22.7. 
The angular separation from the afterglow is 1.2".