TITLE:   GCN CIRCULAR
NUMBER:  23593
SUBJECT: GRB 181228A: possible NOT optical detection
DATE:    18/12/31 00:02:45 GMT
FROM:    Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>

D. Xu (NAOC), D.B. Malesani (DAWN/NBI/DTU and DARK/NBI), J.P.U. Fynbo 
(DAWN/NBI and DAWN/DTU), M.I. Andersen (NBI), T. Pursimo (NOT) report:

We observed the field of GRB 181228A (Moss et al., GCN 23570) using the 
2.56m Nordic Optical Telescope (NOT) equipped with ALFOSC, starting at 
23:56:20 UT on 2018-12-28, i.e., 21.05 hr after the BAT trigger. We 
obtained 3x300s unfiltered frames and 3x300s frames in the Sloan i-band.

There is a weak detection in our stacked image at the REM position 
(D'Avanzo et al., GCN 23575), thus also being consistent with the 
enhanced XRT error circle (Beardmore et al., GCN 23574). The above 
position is not consistent with that of MASTER OT reported in Lipunov et 
al. (GCN 23576). The NOT source has m(i)~25.0+/-0.5, calibrated with 
nearby PanSTARRS stars, and thus it could be the optical counterpart of 
GRB 181228A.