TITLE: GCN CIRCULAR NUMBER: 43959 SUBJECT: EP260306a: Mondy optical upper limit DATE: 26/03/11 10:31:25 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), E. Klunko (ISTP), N. Pankov (IKI), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the fast X-ray transient EP260306a (Huang et al., GCNs 43930, 43937) using the AZT-33IK 1.5m telescope of the Mondy observatory on March 7, 8, and 9 taking several 120-seconds frames in the R band. In the stacked frame of the three epochs we do not detect the optical counterpart reported previously (Li et al., GCN 43929; Globus et al., GCN 43931; Ma et al., GCN 43933; Levan et al., GCN 43934). Preliminary photometry of the galaxy and observational details are the following: Date UT start t-T0 Exp. Filter Obj. Err. UL Site/Telescope (mid,days) (n*s) (3sigma) 2026-03-07 15:44:24 1.61672 33*120 R n/d n/d 22.8 Mondy/AZT-33IK 2026-03-08 14:30:42 2.57040 40*120 R n/d n/d 22.1 Mondy/AZT-33IK 2026-03-09 16:24:33 3.64947 40*120 R n/d n/d 23.2 Mondy/AZT-33IK The photometry is based on nearby USNO-B1.0 stars (R2-magnitudes) and is not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...