TITLE: GCN CIRCULAR NUMBER: 44173 SUBJECT: EP260329b: Mondy and Assy-Turgen optical upper limits DATE: 26/04/01 09:25:28 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), E. Klunko (ISTP), D. Anarbek (FAI), M. Krugov (FAI), A. Pozanenko (IKI), N. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260329b (Song et al., GCN 44142; EP Team, GCN 44155) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several 40-second expositions in R-band, and with the AZT-20 telescope of Assy-Turgen observatory taking several 30-second exposures in r' filter on Mar. 29. In the stacked frames we do not detect the optical counterpart reported previously (Li et al., GCN 44139; Zhu et al., GCN 44140; Eyles-Ferris et al., GCN 44144; Aryan et al., GCN 44147; Lipunov et al., GCN 44150; Mo et al., GCN 44163; O'Neill et al., GCN 44169). Preliminary photometry and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-03-29 15:24:19 0.22110 90*40 R n/d n/d 21.1 Mondy/AZT-33IK 2026-03-29 19:57:04 0.40444 80*30 r n/d n/d 21.6 Assy-Turgen/AZT-20 The photometry is based on several nearby stars from the SDSS-DR16 catalogue (Lupton transformations were used for the R-band values) and is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/44173. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...