TITLE: GCN CIRCULAR NUMBER: 41807 SUBJECT: EP250911a: SVOM/VT optical observation DATE: 25/09/12 03:27:06 GMT FROM: Yinuo Ma <mayn@bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of EP250911a detected by EP/WXT (Liang et al., GCN 41788). SVOM/VT began observing the field at 2025-09-11T15:33:30 UTC, 6.584 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Quirola-Vasquez et al., GCN 41790, Angulo et al., GCN 41793; Lai et al., GCN 41801; Moskvitin & Spiridonova, GCN 41805) at a location consistent with Swift XRT position (Evans et al., GCN 41802) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 6.945 | 27*100 | VT_B | 22.06 | 0.08 6.945 | 27*100 | VT_R | 20.87 | 0.05 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...