TITLE: GCN CIRCULAR NUMBER: 42926 SUBJECT: EP251118a: Mondy, CrAO, Assy and SAO RAS/Zeiss-1000 optical observations DATE: 25/12/01 18:59:42 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. A. Volnova (IKI), A. S. Pozanenko (IKI), A. S. Moskvitin (SAO RAS), E. Klunko (ISTP), V. Rumyantsev (CrAO), M. Krugov (FAI), O. I. Spiridonnova (SAO RAS), N. S. Pankov (IKI) report on behalf of IKI-GRB-FuN: We observed the field of the transient EP251118a (Jiang et al., GCN 42749) detected by the Einstein Probe Wide-field X-ray Telescope (EP WXT), with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) on Nov. 20 and 24 in R filter, with the ZTSH telescope of CrAO on Nov. 20 and 22 in B and R bands, with the AZT-20 1.5m telescope of Assy-Turgen observatory on Nov. 21 in Sloan r filter and Zeiss-1000 of SAO RAS on Nov. 30 in Rc-filter. The optical counterpart (Malesani et al., GCN 42751; Lipunov et al., GCN 42755; An et al., GCN 42756; Belkin et al., GCN 42758; Yadav et al., GCN 42760; Busmann et al., GCN 42763; Francile et al., GCN 42767; Urquijo-Rodríguez et al., GCN 42773; Li et al., GCN 42776; Lee et al., GCN 42780; Moskvitin and Spiridonova, GCN 42785; Gupta et al., GCN 42787; Liu et al., GCN 42793; Aryan et al, GCN 42798; Gupta et al., GCN 42810) is detected in the stacked frame of each epoch. However the flux of the optical transient might be affected by the nearby red star SDSS J081239.57+105619.8 (r_SDSS = 21.911+/-0.178, g-r ~ 3 mag) located in 2.5 arcsec to the East. Some of our preliminary PSF photometry and observational details are the following: Date UT start t-T0 Exp. Filter OT Err. UL Site/Instrum (mid,days) (n*s) (3sigma) 2025-11-20 18:58:01 2.12539 45*120 R 21.45 0.11 22.4 Mondy/AZT-33IK 2025-11-20 21:40:22 2.23886 42*120 R 21.29 0.10 23.2 CrAO/ZTSh 2025-11-20 23:13:01 2.31556 51*120 B 21.02 0.11 23.1 CrAO/ZTSh 2025-11-21 19:57:19 3.16164 57*60 r 22.39 0.08 23.8 Assy/AZT-20 2025-11-22 22:55:20 4.29925 48*120 R 21.62 0.17 22.5 CrAO/ZTSh 2025-11-24 19:51:39 6.15840 36*120 R 23.1 0.4 22.5 Mondy/AZT-33IK 2025-11-30 01:49:42 11.40863 12*300 Rc 22.90 0.15 24.0 SAO/Zeiss-1000 The photometry is calibrated using several nearby stars, USNO-B1.0 B2, R2 magnitudes for AZT-33IK, ZTSh and Zeiss-1000 data, and SDSS r magnitudes for AZT-20 data, all magnitudes are not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42926. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...