TITLE: GCN CIRCULAR NUMBER: 38703 SUBJECT: GRB 241228A: NOT optical upper limits DATE: 24/12/29 10:04:07 GMT FROM: Zipei Zhu at NAOC zpzhu@nao.cas.cn

Z.P. Zhu (NAOC), J. T. Palmerio (CEA/Irfu), J. An, D. Xu (NAOC), D. B. Malesani (DAWN/NBI and Radboud Univ.), T. Pursimo (NOT) report on behalf of a large collaboration:

We observed the field of GRB 241228A detected by Swift (D'Elia et al., GCN 38681), using the ALFOSC instruments mounted on the Nordic Optical Telescope (NOT), with 3 x 300 s in the SDSS-r band and 5 x 200 s photometry in the SDSS-z band. Observations started at 21:10:46 UT on 2024-12-28, i.e. 0.72 day after the trigger.

No new source is detected within the Swift/XRT enhanced error circle (Evans et al., GCN 38683), being consistent with the previous reports (Kuin et al., GCN 38685; Mohan et al., GCN 38689; Lipunov et al., GCN 38693), down to the 5-sigma upper limits of r > 22.0 (AB) and z > 20.5 (AB), calibrated with nearby Pan-STARRS stars without Galactic extinction correction.

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