TITLE: GCN CIRCULAR NUMBER: 44538 SUBJECT: GRB 260511A: SVOM/VT optical observation with VHF data DATE: 26/05/11 09:18:19 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> C. Wu (NAOC), J. T. Palmerio (CEA/Irfu), Y.N. Ma, L. P. Xin, Y. L. Qiu, H. L. Li (NAOC), L. Zhang (IHEP), D. F. Kong (GXU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2026-05-11T06:13:32 UTC (T0), SVOM performed an automatic slew on the burst location ( Godet et al., GCN 44532; Fermi GBM team, GCN 44529;Preis et al., GCN44531). SVOM/VT took images of the field in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, the candidate (Jiang et al., GCN 44533; Akl et al., GCN 44534; Saccardi et al., GCN 44535; Zheng et al., GCN 44536) was clearly detected in VT-VHF data. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded over the course of the VT observations. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | |2026-05-11T06:26:52.000 | 13.32 min | 6*50 sec | -- | 18.61 ± 0.02 | |2026-05-11T07:42:49.000 | 89.27 min | 6*50 sec | 21.15 ± 0.08 | 19.65 ± 0.07 | Magnitudes were not corrected for Galactic reddening. ( Note: The missing VT_B magnitude is likely caused by onboard processing interference. ) The color of VT_B - VT_R = 1.5 is in line with the expectations of an event at redshift z < 4. Further follow-up is encouraged. 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/44538. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...