D. Xu (NAOC), D. B. Malesani (DTU Space), P. Galindo (NOT), Z.P. Zhu
(NAOC, HUST), D. A. Kann (HETH/IAA-CSIC), report on behalf of a larger
We observed the field of GRB 201223A (Gropp et al., GCN 29158) using the
2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera.
We obtained 2x120s Sloan r-band frames starting at 02:21:52 UT on
2020-12-24, i.e., 8.4 hr after the BAT trigger.
The previously reported optical afterglow (Lipunov et al. GCN 29157;
Gropp et al., GCN 29158; Zhu et al. GCN 29159; Hu et al. GCN 29160;
Hosokawa et al. GCN 29164; Romanov et al. GCN 29165; Xin et al. GCN
29166; Belkin et al., GCN 29167; Kumar et al., GCN 29168) is not
detected in the stacked image, down to a limiting magnitude of r > 22.0 mag.
Further analysis of our previous NEXT observations (Zhu et al. GCN
29159) shows that the afterglow is decaying as F_rband ~ t^(-\alpha),
where \alpha = 1.1 since the very beginning. The afterglow would be
slightly fainter than 22.0 mag if this powerlaw decay is extrapolated
until the NOT observational time, being consistent with the observed NOT
upper limit. So the afterglow could be decaying in a single powerlaw
until the NOT observation or have broken to a steeper decay before the