TITLE: GCN CIRCULAR NUMBER: 39449 SUBJECT: EP250223a: TRT optical afterglow observation DATE: 25/02/24 11:34:23 GMT FROM: sqjiang at NAOC <sqjiang@bao.ac.cn> J. An, S.Q. Jiang, N.C. Sun (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), Z. Fan, W.X. Li, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250223a detected by EP (Lian et al., GCN 39429; Wang et al., GCN 39448), and observed by Swift/XRT (Kennea et al., GCN 39437), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 00:37:15.66 UTC on 2025-02-24, i.e., 9.544 hrs after the EP trigger, and a series of 200 s frames were obtained in B, V, R and I bands. The optical afterglow (Wu et al., GCN 39439; Guo et al., GCN 39447; Izzo et al., GCN 39441; Xin et al., GCN 39445; Pérez-Fournon et al., GCN 39440; Hauptmann et al., GCN 39436; Levan et al., GCN 39438) is clearly detected in our stacked images with: | T (mid) - T0 (hours)| band | mag | error | | 9.816 | B | 21.32 | 0.14 | | 9.996 | V | 20.17 | 0.07 | | 10.176 | R | 19.86 | 0.07 | | 10.356 | I | 19.41 | 0.12 | calibrated with Panstarrs-DR2 stars in the field and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...