TITLE: GCN CIRCULAR NUMBER: 8645 SUBJECT: GRB 081203A: optical observations DATE: 08/12/10 02:07:24 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev, K. Antonyuk (CrAO), M. Andreev(Terskol Branch of Institute of Astronomy), A. Pozanenko (IKI) on behalf of larger GRB follow up collaboration report: We observed the field of GRB 081203 (Parsons et al, GCN 8595) with the AZT-11 telescope of CrAO observatory starting Dec. 03 (UT) 15:44:29 under good weather conditions and seeing of about ~2 arcsec. Several exposures were obtained in VRI bands up to 17:13:56 and then between Dec. 04 (UT) 01:19:13 - 02:47:51. Coordinates of the afterglow are RA(J2000)= 15:32:07.58 Dec(J2000)= +63:31:14.8 with uncertainty of 0.2 arcsec which is compatible with the coordinates of the afterglow (Parsons et al, GCN 8595). Preliminary photometry based on SDSS star J153200.06+633229.9 (RA(J2000)=15:32:00.01 Dec(J2000)=+63:32:30.4) assuming V=17.28 R=16.85 I=16.46 is following T0+ Filter Exp. mag. s s 6528 V 180 16.84 +/-0.02 6712 R 180 16.63 +/-0.02 6896 I 180 16.22 +/-0.02 11524 V 180 17.68 +/-0.05 11708 R 180 17.53 +/-0.03 11892 I 180 17.15 +/-0.04 41196 R 3x180 20.27 +/-0.15 46144 R 3x180 20.20 +/-0.14 While light curves in a time interval 6500 - 12000 s after burst onset in R and I bands look similar with a power law decay index of about 0.66, the power law decay index in V-band is ~0.59 and one can suggest a spectral variability of the afterglow. Also we observed steep decay between 12000 - 46000 s with a power law index of about 1.9.