[vsnet-grb-info 27427] GRB 210218A: NEXT optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29530
SUBJECT: GRB 210218A: NEXT optical upper limit
DATE:    21/02/18 14:28:05 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu at nao.cas.cn>

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

We observed the field of GRB 210218A (Sbarufatti et al., GCN 29529) 
using the NEXT-0.6m optical telescope located at Nanshan, Xinjiang, 
China. Observations automatically started at 13:36:52 UT on 2021-02-18, 
i.e., 93 s after the BAT trigger. We obtained 3x40 s, 4x60 s and 12x90 s 
frames in the Sloan r-filter.

No credible optical transient is detected in our stacked image within 
the Swift/BAT error circle, down to a limiting magnitude of r ~ 20.4, 
calibrated with the nearby PanSTARRS field.