TITLE: GCN CIRCULAR NUMBER: 44634 SUBJECT: GRB 260515A: SVOM/VT optical observations DATE: 26/05/16 03:45:58 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, A. Saccardi (CEA/Irfu) report on behalf of the SVOM/VT team. SVOM/VT performed observations with automatic slew of GRB260515A triggered by SVOM/ECLAIRs (sb26051504, Brunet et al., GCN 44622). The observation started at 2026-05-15T19:10:54 UTC, i.e., 155 seconds post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. An additional ToO observation was performed started at 2026-05-15T20:59:23 UTC, 1.85 hours post trigger. The optical counterpart (He et al., GCN 44623; Saccardi et al., GCN 44624; Sosnovskij et al., GCN 44625; He et al., GCN 44626; Wu et al., GCN 44628; Dennefeld et al., GCN 44633) with redshift z=0.764 (Malesani et al., GCN 44629) 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 3.00 m VT_B 50 s 16.06 +/- 0.05 mag 3.00 m VT_R 50 s 15.49 +/- 0.04 mag 3.91 m VT_B 26*70 s 21.27 +/- 0.08 mag 3.92 h VT_R 19*70 s 20.93 +/- 0.07 mag During our observations the decay slope changed from 1.3 to 0.8. 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/44634. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...