TITLE: GCN CIRCULAR NUMBER: 44104 SUBJECT: GRB 260310A: LBT optical observations DATE: 26/03/24 14:51:33 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it> Niccolo’ Passaleva, Yu-Han Yang, Narges Shahamt, Eleonora Troja (U Rome) report on behalf of the ERC BHianca team: Following the detection of GRB 260310A by Fermi/GBM and AstroSat CZTI (Fermi GBM team, GCN 43951,43975; AstroSat CZTI collaboration, GCN 43958), we observed the likely counterpart AT2026fgk (discovered by GOTO; O’Neill et al. 2026, TNS Discovery Report 294132) in r and z filters with the Large Binocular Camera (LBC) mounted on the Large Binocular Telescope (LBT). Observations started at 2026-03-18T09:25:06 (~ 8.2 d after the GBM trigger) with an average airmass of 1.3. We detect the source with a preliminary magnitude of r~18.7 AB mag, calibrated using nearby stars from the Legacy Survey DR10 (Dey et al. 2019) catalogue, uncorrected for Galactic extinction. Our measurement is consistent with those at the same observing time reported by Perley et al. (GCN 44096), Volnova et al. (GCN 44060). We acknowledge excellent support from the LBTO and LBT-INAF staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/44104. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...