TITLE: GCN CIRCULAR NUMBER: 44577 SUBJECT: GRB 260511B: LCO optical counterpart detection DATE: 26/05/12 12:22:26 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), A. López-Oramas (IAC and ULL), and D. Aguado (IAC and ULL) We report on Las Cumbres Observatory (LCO) observations of the long GRB 260511B, detected by Fermi GBM (Fermi GBM team, GCN circ. 44542; Roberts et al., GCN circ. 44554), SVOM ECLAIRs and MXT (Godet et al., GCN circ. 44543), NuSTAR (Waratkar and Grefenstette, GCN circ. 44556), and AstroSat (Arya et al., GCN circ. 44560). We observed the field of GRB 260511B with one of the two LCO 1-m telescopes equipped with Sinistro cameras located at the LCO node at McDonald Observatory, Texas, in the SDSS r´ (300 sec), g' (200 sec), and i' (200 sec) filters. The first observation, in the SDSS r' filter, started on 2026-05-12 at 03:00:47 UT, 16.00 hours after the Fermi and SVOM trigger. The optical conterpart, first reported by Wu et al. (GCN circ. 44547), at a redshift of z = 2.006 (de Ugarte Postigo et al., GCN circ. 44565; Wang et al., GCN circ. 44571; and Adami et al., GCN circ. 44573), is clearly detected in our LCO images. The AB magnitudes, calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction are: r' = 19.81 +/- 0.06 (mid-time 16.05 hours after the trigger) g' = 20.21 +/- 0.06 (mid-time 16.67 hours after the trigger) i' = 19.71 +/- 0.07 (mid-time 16.73 hours after the trigger) These results are consistent with other optical and near-IR detections of the afterglow (Wu et al., GCN circ. 44547; Sasada et al., GCN circ. 44549; Jiang et al., GCN circ. 44551; Wu et al., GCN circ. 44552; Li et al., GCN circ. 44557; Vijaykumar et al., GCN circ. 44561; de Ugarte Postigo et al., GCN circ. 44565; Lee et al., GCN circ. 44567; Li et al., GCN circ. 44568; Wang et al., GCN circ. 44571; Belkin et al., GCN circ. 44572; Adami et al., GCN circ. 44573; Saccardi et al., GCN circ. 44574); and Rajabov et al., GCN circ. 44576). 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/44577. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...