TITLE: GCN CIRCULAR NUMBER: 38630 SUBJECT: GRB 241218A: NOT optical upper limits DATE: 24/12/19 02:10:25 GMT FROM: syfu@nao.cas.cn

S.Y. Fu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), Z.P. Zhu, X. Liu, D. Xu (NAOC), L. Cotter (UCD), A. Amanda Djupvik (NOT) report on behalf of a large collaboration:

We observed the field of GRB 241218A detected by Swift (Williams et al., GCN 38601) using the StanCam instrument mounted on the Nordic Optical Telescope (NOT), 3 x 300 s in the Bessel R band and 5x200 s in the Sloan z band frames were obtained. Observations started at 04:37:19 UT on 2024-12-18, i.e., 4.5 hr after the trigger.

No new source is detected in the stacked frames within the enhanced Swift/XRT error circle (Beardmore et al. GCN 38604), with the limiting magnitudes of R > ~ 21.7 (Vega, converted from r-band, Lupton 2005) and z > ~ 21.0 (AB), calibrated with nearby Pan-STARRS stars and without Galactic extinction correction.

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