TITLE:   GCN CIRCULAR
NUMBER:  29768
SUBJECT: GRB 210406A: BOOTES-4/MET optical upper limit
DATE:    21/04/06 21:05:50 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

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 210406A by INTEGRAL (Mereghetti et al. GCNC 29767), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to the burst starting on Apr 6 at 17:13:27 UT  (~2 min after trigger). No new source is detected within the refined IBIS position (Mereghetti et al. GCNC 29767) down to 20.7 mag in the co-added image (878 s on the aggregate, clear filer). The non-detection is consistent with the limit reported by MASTER (Lipunov et al. GCNC 29766).

We thank the staff at Lijiang observatory for their excellent support.