TITLE:   GCN CIRCULAR
NUMBER:  33068
SUBJECT: GRB 221216A: Nanshan/NEXT optical upper limits
DATE:    22/12/16 13:20:08 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

T.H. Lu, X. Liu (NAOC), Z.P. Zhu (NAOC, HUST), S.Q. Jiang, S.Y. Fu, D. 
Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of GRB 221216A detected by Swift (Dichiara et al., 
GCN 33067) using the NEXT-0.6m telescope located at Nanshan, Xinjiang, 
China. We obtained a series of frames in the Sloan r-band and z-band, 
starting at 11:23:09 UT on 2022-12-16, i.e., 109s after the BAT trigger.

No optical source is detected in our stacked images at the XRT position 
(Dichiara et al., GCN 33067), with upper limits as follows:

T_mid-T0 (min)    Filter   Upper limit(3-sigma)
     14.26                 r          >17.5
     14.90                 z          >16.5

calibrated with the nearby SkyMapper field and not corrected for 
Galactic extinction.