TITLE:   GCN CIRCULAR
NUMBER:  31279
SUBJECT: GRB 211221A: BOOTES-4/MET optical upper limit
DATE:    21/12/22 13:49:01 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

Y.-D. Hu, T.-R. Sun, A. J. Castro-Tirado, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, 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 211221A by Swift (Page et al. GCNC 31273), the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) automatically responded to this burst starting on Dec. 21 at 20:51:37 UT (~177 sec after trigger). No new source is detected at the position reported by Swift-XRT (Page et al. GCNC 31273) which down to 19.7 mag in the co-added image of first achieved 10 x 20 s exposure frames in the clear filter. This non-detection is consistent with the reports from UVOT (Page et al. GCNC 31273), MASTER (Lipunov et al. GCNC 31274), NOT (Malesani et al. GCNC 31276) and MeerLICHT (Groot et al. GCNC 31277).

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