TITLE: GCN CIRCULAR NUMBER: 43212 SUBJECT: GRB 251222A / EP251222b: LCO detection of the optical counterpart DATE: 25/12/23 10:34:06 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es> I. Pérez-Fournon (IAC and ULL), F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia, E. Lekaroz-Urriza, M. Quintana-Ansaldo (all ULL), and A. López-Oramas (IAC and ULL) Following the detection of the long GRB 251222A / EP251222b detected by Fermi/GBM (The Fermi GBM team, GCN #43186; and Preis and Greiner, GCN #43190), SVOM ECLAIRs, GRM, and MXT (Yang et al., GCN #43188), EP/WXT (Guo et al., GCN #43201), SVOM/GRM (Wang et al., GCN 43202) and Swift-XRT (Evans, GCN #43191, source 1 of https://www.swift.ac.uk/ToO_GRBs/00021895/), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Sutherland Observatory, South Africa. The observation, a single exposure of 300 sec in the SDSS r' filter, started on 2025-12-22 at 18:48:07 UT, about 1.7 hours after the SVOM and Fermi triggers. The optical counterpart detected by SVOM/VT (Palmerio et al., GCN #43189; and Li et al., GCN #43203) is clearly detected in our image with a magnitude of r' = 18.55 +/- 0.03 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical and near-IR detections (Palmerio et al., GCN #43189; An et al., GCN #43194; Calapai et al., GCN #43195; Durbak et al., GCN #43197; Li et al., GCN #43203; Saccardi et al., GCN #43204; Gupta et al., GCN #43207; Saccardi et al., GCN #43208; and Kumar et al., GCN #43209). We notice a minimum in the light curve at the time of our LCO r'-band and the Calapai Observatory (Calapai et al., GCN #43195) observations. Saccardi et al. (GCN #43204) have reported a spectroscopic redshift of z = 3.171. This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-008, SGLF and Superluminous Supernovae surveys). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/43212. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...