TITLE:   GCN CIRCULAR
NUMBER:  31276
SUBJECT: GRB 211221A: NOT optical limits
DATE:    21/12/22 01:41:13 GMT
FROM:    Daniele B Malesani at Radboud U  <d.malesani@astro.ru.nl>

D. B. Malesani (Univ. Radboud and DAWN/NBI), Z. Zhu (NAOC/CAS), A. 
Viitanen (Univ. Helsinki and NOT), E. Biancalani (Leiden Obs. and NOT) 
report on behalf of a larger collaboration:

We observed the field of the solstice GRB 211221A (Page et al., GCN 
31273) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC 
camera. Observations were carried out under good conditions in the r and 
z bands, with mean times 2021 Dec 22.00 and 22.01 UT, respectively (3.2 
and 3.5 hr after the GRB). The exposure times were 3x300 (in r) and 
5x200 s (in z).

We detect no new objects inside or close to the UVOT-enhanced XRT error 
circle (Evans et al., GCN 31275), down to (preliminary) limits:

r > 23.5 AB
z > 23.0 AB

Calibration of the photometry is relative to nearby stars from the 
Pan-STARRS catalogue.