TITLE: GCN CIRCULAR NUMBER: 41181 SUBJECT: GRB250727A: SVOM/VT optical upper limit DATE: 25/07/27 23:03:23 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, Y. L. Qiu, L. P. Xin, 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), J. X. Cao (GXU) report on behalf of the SVOM team. SVOM/VT performed ToO follow-up observations on the GRB 250727A (SVOM burst-id sb25072701, Cao et al., GCN 41176) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started on 2025-07-27T12:45:24 UT, about 1.82 hours after the SVOM T0 time. No uncatalogued sources are detected in single or stacked images at the position of the Swift/XRT (Evans et al., GCN 41180), compared to the Legacy survey. The 3 sigma upper limit magnitudes are derived as below: Mid_time | Band | Exposure Time | Upper limit (AB) 2.16 hour VT_B 36*70 sec 23.5 mag 2.16 hour VT_R 35*70 sec 23.4 mag Also no apparent variation is found for the catalogued sources that lie within the errorbox of the Swift/XRT source 2 (Evans et al., GCN 41180). 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/41181. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...