TITLE: GCN CIRCULAR NUMBER: 44058 SUBJECT: GRB 260310A/AT2026fgk: LBT near-infrared observations DATE: 26/03/20 17:40:46 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 J and K filters with the LUCI near-infrared imager mounted on the Large Binocular Telescope (LBT). Observations started at 2026-03-16T08:07:32 (~ 6.2 d after the GBM trigger) with an average airmass of 1.3. We detect the source with a preliminary magnitude of J~18.03 AB mag, calibrated using nearby stars from the 2MASS catalog (Skrutskie et al. 2006), uncorrected for Galactic extinction. Compared with previous near-infrared observations (Li et al., GCN 43993; Stein et al., GCN 43996; Brivio et al., GCN 44004), our measurement is consistent with a fading slope of 0.7. We acknowledge excellent support from the LBTO and LBT-INAF staff. View this GCN Circular online at https://gcn.nasa.gov/circulars/44058. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...