[vsnet-grb-info 19843] GRB 170921A: Nanshan optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21907
SUBJECT: GRB 170921A: Nanshan optical upper limit
DATE:    17/09/22 00:33:24 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu at nao.cas.cn>

H.X. Feng (NAOC), Y.D. Hu (IAA-CSIC), D. Xu, Z.P. Zhu (NAOC), X. Zhang, T.Z. Yang, J.Z. Liu, A. Esamdin, L. Ma (XAO), Y. Qin (Geneva Obs.) report:  We observed the field of long GRB 170921A (D'Ai et al., GCN 21901) using the 1m telescope located at Nanshan, Xinjiang, China. We obtained 3*180s R-band frames, starting at 15:52:35.04 UT on 2017-09-21 (i.e., 1.39 hr after the BATtrigger).  No optical source is detected at the XRT position (Beardmore et al., GCN 21906) in the stacked image, down to a limiting magnitude of m(R)~20.3, calibrated with the USNO-B1 catalog.