TITLE: GCN CIRCULAR NUMBER: 43280 SUBJECT: GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening DATE: 25/12/31 12:31:28 GMT FROM: luca.izzo@inaf.it L. He (NAOC), L. Izzo (INAF/OACN and DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), K. Valeckas (NOT & NBI) report on behalf of a larger collaboration: We observed the optical counterpart (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi, GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265; Starling et al., GCN 43267; He et al., GCN 43269; Breeveld et al., GCN 43271; Sankar et al., GCN 43279) of GRB 251230A / EP251230a (Lanava et al., GCN 43252; Wang et al., GCN 43259; Osborne et al., GCN 43263), using the Nordic Optical Telescope (NOT), equipped with the ALFOSC camera. A series of 10 x 150s exposures was taken in the i band starting on 2025 Dec 31 at 04:46:27 (1.14 days after the Swift trigger). The afterglow is detected in the final stacked images with an AB magnitude of i = 22.93 +/- 0.09 mag, at a mid-time of 1.15 days after the trigger. Our photometry was calibrated using nearby stars from the Pan-STARRS catalog and is not corrected for Galactic extinction. This new epoch suggests that the fading of the optical afterglow has slowed down considerably from the decay index reported by He et al. GCN 43269. We note that, based on the colour measured in our earlier epoch, the r-band upper limit reported by Sankar et al. GCN 43279 suggests a possible rebrightening. Happy New Year to everyone!!! View this GCN Circular online at https://gcn.nasa.gov/circulars/43280. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...