TITLE: GCN CIRCULAR NUMBER: 21795 SUBJECT: GRB 170903A: Nanshan optical upper limit DATE: 17/09/03 15:01:49 GMT FROM: Dong Xu at NAOC/CAS H.X. Feng, D. Xu, Z.P. Zhu (NAOC), S.G. Ma, T.Z. Yang, J.H. Liu, P. Zong, H.B. Niu, J.Z. Liu, A. Esamdin, L. Ma (all XAO), Y.D. Hu (IAA-CSIC), Y. Qing (Geneva Observatory) report: We observed the field of GRB 170903A (Markwardt et al., GCN 21793) using the 1m telescope located at Nanshan, Xinjiang, China. We obtained 3x180s R-band frames, starting at 14:08:09 UT on 2017-09-03, i.e., 1.317 hr after the burst. No optical source is detected at the XRT position (Campana et al., GCN 21794) in the stacked image, down to a limiting magnitude of m(R)~21.3, calibrated with the nearby SDSS field.