TITLE: GCN CIRCULAR NUMBER: 43694 SUBJECT: GRB 260208A: LCO detection of the optical counterpart DATE: 26/02/11 12:33:24 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 bright and long GRB 260208A detected by Fermi GMB (Fermi GBM Team, GCN #43635; Mukherjee and Meegan, GCN #43673), Fermi LAT (Longo et al., GCN #43645), Swift-XRT (Dichiara et al., GCN #43652; Longo et al., GCN #43643), GECAM-B (Luo et al., GCN #43658), NuSTAR (Waratkar et al., GCN #43674), and Glowbug (Cheung et al., GCN #43675), we observed the field with one of the three Las Cumbres Observatory (LCO) 1-m telescopes located at the LCO node at Cerro Tololo Inter-American Observatory (CTIO), Chile. The observation, a single exposure of 300 sec in the SDSS r' filter, started on 2026-02-09 at 07:48:36 UT, about 26.69 hours after the Fermi trigger. The optical counterpart AT 2026ciw (MASTER OT J133855.62+334806.9, GOTO26aob, ZTF26aafswob) first detected by Podesta et al. (MASTER, GCN #43640) and Wortley et al. (GOTO, GCN #43641) is detected in our image with an AB magnitude of r' = 20.92 +/- 0.17, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. This result is consistent with the late evolution of the optical afterglow of this redshfit z = 2.36 GRB (Dimple et al., GCN #43662). Optical detections have been reported by Podesta et al. (GCN #43640), Wortley et al. (GCN #43641), Ma et al. (GCN #43655), Ahumada et al. (GCN #43657), Dimple et al. (GCN #43661), Dimple et al. (GCN #43662), Magnani et al. (GCN #43664), Gupta et al. (GCN #43665), Volnova et al. (GCN #43666), and Bochenek et al. (GCN #43676). This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2026A-011, 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/43694. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...