TITLE: GCN CIRCULAR NUMBER: 40645 SUBJECT: GRB 250605A: VT optical upper limit DATE: 25/06/06 15:40:20 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, 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/VT conducted ToO follow-up observations of the GRB 250605A (Gupta et al., GCN 40633, Melandri et al., GCN 40644). The observation started on 2025-06-06T05:02:39 UT in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.  No uncatalogued sources are detected in single or stacked images within the Swift/XRT error box (Evans et al., GCN 40642) and the possible optical candidate reported by Gompertz et al. (GCN 40634). The 3 sigma limit magnitudes are derived as below: Mid time | Band | Exposure Time | 3 sigma limit magnitude 11.28 hour VT_B 59*70 sec >23.6 mag 11.28 hour VT_R 59*70 sec >23.6 mag 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/40645. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...