TITLE: GCN CIRCULAR NUMBER: 44044 SUBJECT: GRB 260310A / AT2026fgk: SVOM/VT optical observations DATE: 26/03/18 07:47:29 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, X. H. Han, J. Wang, Y. Xu, 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. T. Palmerio (CEA/Irfu)，J. X. Cao (GXU) report on behalf of the SVOM/VT team. SVOM/VT performed several ToO observations of the field of GRB 260310A detected by Fermi (Fermi GBM team, GCN 43951) and AstroSat(Salunke et al., GCN 43958) from 2026-03-14 to 2026-03-17 in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The reported optical counterpart AT2026fgk discovered by GOTO(O'Neill et al. 2026, TNS Discovery Report 294132) and observed by other observatories (Lipunov et al., GCN 43954; Konno et al., GCN 43974, Hinds et al., GCN 43977; Lipunov et al., GCN 43978; Martin-Carrillo et al., GCN 43979, Moren Méndez et al., GCN 43980; de Ugarte Postigo et al., GCN 43984, Pursiainen et al., Becerra et al., GCN 43991; Martin-Carrillo et al., GCN 44000; Watson et al., GCN 44001; Lai et al., GCN 44002; L. Izzo, GCN 44003; Brivio et al., GCN 44004; Rhodes et al., GCN 44005; Moskvitin et al., GCN 44006; Brosio et al., GCN 44021; Pawar et al., GCN 44022; Belkin and Shrestha, GCN 44043) is clearly detected in single frames in both channels. The preliminary measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 5.26 day VT_R 70 sec 18.44 +/- 0.05 mag 5.26 day VT_B 70 sec 18.94 +/- 0.05 mag 7.35 day VT_R 70 sec 18.65 +/- 0.05 mag 7.35 day VT_B 70 sec 19.15 +/- 0.05 mag Our photometry was 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 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/44044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...