TITLE: GCN CIRCULAR NUMBER: 44598 SUBJECT: GRB 260509A: SVOM/VT optical observations DATE: 26/05/13 15:17:36 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, Y. L. Qiu, C. Wu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio, D. Götz and D. Adrien (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations of GRB260509A triggered by SVOM/ECLAIRs (sb26050905, Götz et al., GCN 44504). The observation started at 2026-05-09T22:12:49 UTC, about 21.66 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The afterglow (O’Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Alvarez et al., 44509; Zheng et al., GCN 44510; Lipunov et al., GCN 44512; Belkin et al., GCN 44513; Corcoran et al., GCN 44514; Bochenek et al., GCN 44516; Moskvitin et al., GCN 44563; Mo et al., GCN 44590) was detected clearly in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 22.08 m VT_B 50 s 20.05 +/- 0.07 mag 22.08 m VT_R 50 s 19.47 +/- 0.06 mag 8.17 h VT_B 16*100 s 21.76 +/- 0.09 mag 8.24 h VT_R 11*100 s 21.48 +/- 0.09 mag The light curves shows fading and brightening at early epochs, followed by a temporal decay with a slope of −1 in the late phase during our observations. 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/44598. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...