[vsnet-grb-info 7068] GRB081203B: optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8651
SUBJECT: GRB081203B: optical observations
DATE:    08/12/11 05:43:29 GMT
FROM:    Vladimir Sokolov at SAO RAS  <sokolov at sao.ru>

T.A. Fatkhullin (SAO RAS, Niznij Arkhyz), E. Sonbas (SAO RAS, Niznij Arkhyz; 
University of Cukurova, Turkey), A.J. Castro-Tirado (IAA-CSIC Granada) & 
A.Pozanenko (IKI RAS, Moscow) on behalf of larger collaboration, report:

We observed the field of the GRB081203B (P. Schady et al., GCN 8606; Andreev 
et al, GCN 8608) in the Rc-band with the 6-m telescope of the SAO RAS in 
Caucasus. In total two 3-min exposures were obtained. The optical transient 
(OT) is clearly detected in the both images. Using 4 USNO B1.0
stars we estimated the brightness of the OT as 
R = 21.81 +/- 0.10  at the epoch of  T-T0 = 3.534 days. 
We assumed a burst time of 13:52:02 UT (Copete et al., GCN 8600).

Combining our data with ones from the GCN 8608, 8626, 8631 and 8637 
we estimate the observed power-law index of the light curve as alpha ~ 1.0.

In the same night we also obtained 2x600sec spectrum of the object near 
morning twilight. The VPHG550G grism was used with spectral resolution of 
FWHM=10A. Inspection of the integrated spectrum showed no strong emission 
lines in the range of 4000-7500AA.

The 3-min R-band image can be downloaded from 
ftp://ftp/pub/grb/GRB081203B/GRB081203B_R01.jpg

This message can be cited