TITLE: GCN CIRCULAR NUMBER: 44582 SUBJECT: GRB 260511B: SAO RAS optical observations DATE: 26/05/12 15:32:19 GMT FROM: Alexander Moskvitin at SAO RAS <mosk@sao.ru> A. Moskvitin (SAO RAS) and A. Pozanenko (IKI), report on behalf of GRB the follow-up team. We observed the field of the GRB 260511B discovered by Fermi (The Fermi GBM team, GCN 44542; Roberts, GCN 44554), SVOM (Godet et al., GCN 44543), NuSTAR (Waratkar and Grefenstette, GCN 44556), AstroSat CZTI (Arya et al., GCN 44560); EP-FXT (Fu et al., GCN 44578) with the Zeiss-1000, 1m telescope of the SAO RAS equipped with the CCD photometer. Observations were performed in B, V, Rc, Ic filters and started on May 11, 19:08:40 UT (8.14 hours after the trigger). The OT (Wu et al., GCN 44547; Sasada et al., GCN 44549; Jiang et al., GCN 44551; Wu et al., GCN 44552; Vijaykumar et al., GCN 44561; de Ugarte Postigo et al., GCN 44565; Lee et al., GCN 44567; Li et al., GCN 44568; Wang et al., GCN 44571; Belkin et al., GCN 44572; Adami et al., GCN 44573; Saccardi et al., GCN 44574; Rajabov et al., GCN 44576; Pérez-Fournon et al., GCN 44577; Novotný et al., GCN 44580; also detected in NIR by Li et al., GCN 44557) is clearly detected in all frames with the following brightness. Date T_start T_end t_mid-T0, exp, s filter mag +/- err UT hours 2026-05-11T19:14:19--19:54:19 8.56306 3*300 B 19.56 +/- 0.03 2026-05-11T19:20:15--19:40:09 8.49444 2*120 V 19.09 +/- 0.04 2026-05-11T19:08:40--19:43:12 8.42333 3*120 Rc 18.75 +/- 0.02 2026-05-11T19:11:24--19:51:31 8.51542 5*120 Ic 18.50 +/- 0.05 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44582. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...