T.-R. Sun, Y.-D. Hu, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), S. Guziy (Univ. of Nikolaev) and D. R. Xiong, Y. F. Fan, J. M. Bai, C. J. Wang, Y. X. Xin, X. H. Zhao (Yunnan Observatories of CAS) on behalf of a larger collaboration, report:
Following the detection of GRB 210509A by Swift (Page et al. GCNC 29970), we triggered the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) starting on May 9 at 19:32 UT (~5 hr after trigger) with non-optimal conditions (passing clouds and the target being at high airmass). No optical source is detected at the position reported by Swift-XRT (Evans et al. GCNC 29971) down to 17.2 mag in the co-added image (clear filter). Additional observations are ongoing.
We thank the staff at Lijiang observatory for their excellent support.