GCN 45179: GRB 260718A: SVOM/VT optical upper limits

2026-07-18T16:56:45.670Z | rev 0 | event: GRB 260718A
H. L. Li, Y. N. Ma, C. Wu, Y. L. Qiu, L. P. Xin, 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, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), W. L. Zhang (PMO) report on behalf of the SVOM/VT team.

SVOM/VT performed observations with automatic slew to the field of GRB 260718A triggered by SVOM/ECLAIRs (sb26071802, Antier et al., GCN 45177). The observations started at 2026-07-18T12:00:14 UTC, about 44.08 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. 

No credible sources were detected within the error box of ECLAIRs (Antier et al., GCN 45177), compared to the Legacy Survey catalog. The 3σ upper limits of AB magnitudes without corrections for Galactic extinction are as follows:

Mid time  | Band | Exposure Time | 3 sigma upper limit
1.05 hr   VT_B     42*50 s          > 23.2 mag    
1.05 hr   VT_R     38*50 s          > 23.0 mag

This non-detection is consistent with VT VHF upper limits (Ma et al., GCN 45178). 

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.