TITLE: GCN CIRCULAR NUMBER: 42341 SUBJECT: GRB 251017A: SVOM/VT optical observation DATE: 25/10/18 02:40:22 GMT FROM: Liping Xin at NAOC, SVOM <xlp@nao.cas.cn> L. P. Xin, H. L. Li, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team: SVOM/VT performed a Target of Opportunity observation of GRB 251017A detected by Swift/BAT (Gupta et al., GCN 42322) and Glowbug (Woolf et al., GCN 42335;), starting at 2025-10-17T09:17:19 UTC, 37 min after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Mo et al., GCN 42336, Adami et al. GCN 42339) is detected in both channels. Mid-time | exposure time (s) | band | Magnitude (AB) ---------|-------------------|------|----------------- 3.96 h | 27*70 | VT_B | 22.57+/-0.14 3.96 h | 27*70 | VT_R | 20.30+/-0.05 Given the red color from the VT data, it is likely a medium/high redshift burst with a redshift > 4. Our photometry was in AB magnitude and not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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/42341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...