TITLE: GCN CIRCULAR NUMBER: 11837 SUBJECT: GRB 110328A / Swift J164449.3+573451: optical observations DATE: 11/03/30 01:45:38 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (SAI MSU), A. Pozanenko (IKI), E. Klunko (ISTP) on behalf of larger GRB follow up collaboration report: We observed the field of GRB 110328A / Swift J164449.3+573451 (Cummings et al. GCN 11823) with AZT-33IK telescope of Sayan observatory (Mondy) starting on March 28 (UT) 13:46:35, i.e. 6 minutes after second trigger (Barthelmy et al. GCNC 11824). We identified the optical counterpart (Cenko et al. GCN 11827, Leloudas et al. GCN 11830) in the combined image of a total exposure of 67 min. The photometry of the optical counterpart in the combined image is R=21.50 +/- 0.10 and based on the USNO-A2.0 star 1425-08596694 assuming R=16.6. The photometry is still preliminary and calibration of field stars is necessary (Cenko et al. GCN 11827) to confirm the variable nature of the optical counterpart. [GCN OPS NOTE(30apr11): Per author's request, Elunko was changed to Klunko.]