TITLE: GCN CIRCULAR NUMBER: 44103 SUBJECT: EP260321A: Mondy optical observations DATE: 26/03/24 12:34:33 GMT FROM: Nicolai Pankov at IKI <colinsergesen@gmail.com> N. Pankov (IKI), A. Pozanenko (IKI), E. Shekotikhin (IKI), E. Klunko (ISTP), A. Volnova (IKI) report on behalf of IKI-GRB-Fun collaboration: We observed the localization of the EP260321A (Huang et. al, GCN 44068) with the AZT-33IK telescope of the Mondy observatory. We obtained series in the R filter on epochs 2026-03-21, 2026-03-22 and 2026-03-23. The source reported by the Kinder (Lee et al., GCN 44070) and observed till now by (Aryan et al., GCN 44081; Ma et al., GCN 44074; Aguilar-Ruiz et al., GCN 44076; Liang et al., GCN 44079; Aryan et al., GCN 44081; Tanvir et al., GCN 44082; Moran et al., GCN 44083; Ahumada et al., GCN 44084; Liu et al., GCN 44087; Sankar et al., GCN 44089; de Ugarte Postigo et al., GCN 44091; Xu et al., GCN 44092) is clearly visible in the co-add images on all epochs. The early brightening of the source is evident after subtracting the epochs (i.e., 2026-03-23 minus 2026-03-22). The photometry of the host galaxy + the source and observation details are listed below: Date UT start t-T0 Exp. Filter OT+host Err. UL(3sigma) (mid, days) (s) 2026-03-21 14:50:00 0.11785 30x120 R 18.09 0.02 22.7 2026-03-22 16:02:29 1.16819 30x120 R 17.77 0.02 22.7 2026-03-23 14:48:46 2.11561 28x120 R 17.29 0.02 22.8 The photometry was calibrated using nearby USNO-B1.0 stars (R2 mags) and has not been corrected for the Galactic extinction. The photometry of the 2026-03-23 epoch might be affected by the host very slightly, while for other epochs the photometry is significantly contaminated by the host. View this GCN Circular online at https://gcn.nasa.gov/circulars/44103. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...