TITLE: GCN CIRCULAR NUMBER: 15142 SUBJECT: GRB 130831A: Weihai optical observations DATE: 13/08/31 14:29:36 GMT FROM: Dong Xu at DARK/NBI D. Xu (DARK/NBI), C. M. Zhang, C. Cao, S. M. Hu (SDU) report: We observed the field of GRB 130831A (Hagen et al., GCN 15139) using the 1m telescope located in Weihai, Shandong Province, China, and 2x600s SDSS r'-band frames were obtained. The optical afterglow is well detected at the UVOT position in each of the two images with rather fast decaying rate. Following photometry is calibrated with nearby SDSS stars: Mag MagErr MeanTime(T-Ttrigger, hr) 14.35 0.04 0.3356 15.66 0.05 0.6575