TITLE: GCN CIRCULAR NUMBER: 36118 SUBJECT: GRB 240415A: Mondy optical transient detection DATE: 24/04/15 16:15:54 GMT FROM: Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI) report on behalf of GRB-IKI-FuN: We observed the field of GRB 240415A (Fermi GBM team, GCN 36107; Moss et al., GCN 36108, Evans et al., GCN 36109) with 1.5-meter AZT-33IK telescope of Sayan observatory at Mondy. The observations were started on 2024-04-15 (UT) 14:33:22, i.e. ~8 hr since the Fermi GBM trigger. We took 30 frames 120 s each in the R-filter. We detect a possible optical counterpart in the stacked image at coordinates of (J2000) 08:36:45.26 73:08:47.6 with uncertainties of 0.4 arcsec in both coordinates. Preliminary photometry of the optical source is following: Date UT_start MJD Filter Exp. OT err UL(3sigma) (mid, days) (s) 2024-04-15 14:33:22 60415.627345 R 44*120 18.84 0.08 21.9 The magnitudes were calibrated using nearby USNO-B1.0 stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/36118. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...