TITLE: GCN CIRCULAR NUMBER: 42433 SUBJECT: GRB 251025A: SVOM/VT VHF optical upper limit DATE: 25/10/25 11:14:50 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> C. Wu, H. L. Li, L. P. Xin, Y. L. Qiu (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU), W. J. Tan (IHEP) report on behalf of the SVOM/VT team. SVOM/VT began observing the field of GRB 251025A (Wang et al., GCN 42432) at 202025-10-25T09:43:10 UT, 7.8 minutes after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No optical candidate was detected within the position of MXT (Wang et al., GCN 42432), based on a preliminary analysis of the source list and 1-bit subimage downloaded via VHF network. The 3 sigma upper limits are about 21.5 mag in VT_R with an effective exposure time of 6*50 sec at 10.3 min post trigger. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/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/42433. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...