TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4358 SUBJECT: GRB 051211B: optical afterglow DATE: 05/12/16 13:23:45 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia M. Jelínek, A. de Ugarte Postigo, A.J. Castro-Tirado, V. Casanova, D. Martínez, S. Guziy, S. Castillo, S. B. Pandey and J. Gorosabel (IAA-CSIC Granada): report: "We have imaged a 7' x 7' region containing the INTEGRAL error box for GRB 051211B (Mereghetti et al. GCNC 4327) with the 1.5-m OSN telescope at the Observatorio de Sierra Nevada, starting on Dec 11.94 UT (i.e. 25 min after the GRB). A comparison image has been taken on Dec. 15.86 UT. At the position of the X-ray afterglow detected by Swift/XRT (La Parola et al. GCN 4338) we detect one source that has decreased significantly in brightness in our I-band images. Coordinates yield: RA(2000) = 23:02:41.57,Dec(2000) = +55:04:51.5 (+/-0.4"). This is the likely optical afterglow to GRB 051211B. Images are posted at http://www.iaa.es/~deugarte/GRBs/051211B/GRB051211B.gif . An underlying object seems to be present on the DDS-2 (infrared) which may be a bright host galaxy, detected also on our late I-band image. Further observations are encouraged." This message can be quoted. [GCN OPS NOTE(16dec05): This circular was refortted by adding the missing line breaks.]