TITLE: GCN CIRCULAR NUMBER: 44652 SUBJECT: GRB 260515A: CrAO ZTSh BVRI optical observations DATE: 26/05/16 23:52:00 GMT FROM: Alexander Moskvitin at SAO RAS <mosk@sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), V. Rumyantsev (CrAO), N. Pankov (IKI), A. Volnova (IKI) report on behalf of IKI GRB-FuN. We observed the field of the GRB 260515A (Brunet et al., GCN 44622; Wang et al., GCN 44642; Frederiks et al., GCN 44647) with the Shajn 2.6-meter telescope (ZTSh) of the Crimean Astrophysical Observatory (CrAO). We obtained series of 120 s exposures in BVRI filters starting on 2026-05-15 22:10:11 UT (about 3 hours after trigger). The OT (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Malesani et al., GCN 44629; Dennefeld et al., GCN 44633; Li et al., GCN 44634; Antier et al., GCN 44643; Pérez-Fournon et al., GCN 44645; Dimple et al., GCN 44646) is clearly detected in the stacked frames. Details of the photometry is the following. Start_UT, t_mid-T0, exp, filter, mag, err, UL(3 sigma) 2026-05-15T22:54:33 4.79 15*120 B 21.53 0.04 23.9 2026-05-15T22:56:41 4.75 13*120 V 21.30 0.05 23.7 2026-05-15T22:10:11 3.12 5*120 R 20.56 0.04 23.4 2026-05-15T22:20:40 3.29 5*120 R 20.57 0.04 23.4 2026-05-15T22:31:09 3.46 5*120 R 20.65 0.04 23.5 2026-05-15T22:41:44 3.66 6*120 R 20.64 0.03 23.6 2026-05-15T22:56:41 4.26 7*120 R 20.87 0.03 23.7 2026-05-15T23:58:56 5.35 8*120 R 21.03 0.04 23.4 2026-05-15T23:00:57 4.89 15*120 I 20.75 0.05 22.8 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44652. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...