TITLE:   GCN CIRCULAR
NUMBER:  31853
SUBJECT: GRB 220408A: Xinglong-2.16m optical upper limit
DATE:    22/04/08 13:30:31 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

S.Q. Jiang, S.Y. Fu, X. Liu, D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), L.P. 
Xin, J.Y. Wei, G.W. Li (NAOC) report on behalf of a larger collaboration:

We observed the field of GRB 220408A detected by Swift (Caputo et al., 
GCN 31848) and Fermi (Fermi GBM team, GCN 31847) using the 
Xinglong-2.16m telescope equipped with the BFOSC camera. Observations 
were carried out starting at 12:02:32 UT on 2022-04-08 (i.e., 6.27 hr 
since the BAT trigger), and 9x400 s frames in the R-band were obtained.

The previously reported optical counterpart (e.g., Caputo et al., GCN 
31848; Zheng & Filippenko, GCN 31850) is not detected in our stacked 
image, down to a limiting magnitude of R ~ 20.7 (Vega) at 6.79 hr 
post-burst, calibrated with the nearby SDSS field.