TITLE: GCN CIRCULAR NUMBER: 43945 SUBJECT: GRB 260307B: SVOM/VT upper limit with X band data analysis DATE: 26/03/08 06:53:14 GMT FROM: Yinuo Ma <mayn@bao.ac.cn> Y. N. Ma, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, L. P. Xin, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), F. Magnani, A. Foisseau (CPPM) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the burst GRB 260307B (sb26030704) triggered by SVOM/ECLAIRs (Magnani et al., GCN 43940). SVOM/VT began observing the field at 2026-03-07T13:50:41 UTC, 315.5 seconds after T0, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. After quick analyzing the X band data avaliable, the VT-VHF candidate (Palmerio et al., GCN 43942) was not confirmed in either single or stacked X band images. Therefore, we conclude that the VT-VHF candidate is not a real source. Also, no any uncatalogued sources are detected within the error range of MXT (Magnani et al., GCN 43940) down to ~22.5 AB magnitude at the mid time of 10.25 minutes in both VT_B and VT_R. Considering the bright X-ray detection by MXT and non-detection by VT with auto slew, the GRB is an optically dark burst or a high-redshift candidate. Near infrared observations are encouraged. Further data analysis is ongoing. 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/43945. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...