GCN 44190: GRB 260402A / EP260402a: SVOM/VT optical upper limits

2026-04-02T16:30:34.243Z | rev 0 | event: GRB 260402A
H. L. Li, C. Wu, Y. L. Qiu, 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 (CEA/Irfu), W. Tan (IHEP) and R. Li (YNAO) report on behalf of the SVOM/VT team.

SVOM/VT performed observations with automatic slew to the field of GRB 260402A triggered by SVOM/ECLAIRs (sb26032123, Tan et al., GCN 44181), SVOM/GRM (Tan et al., GCN 44181) and Einstein Probe (EP260402a, Zhao et al., GCN 44186). The observation started at 2026-04-02T10:44:07 UTC, approximately 13.8 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. 

No uncatalogued sources are detected in single or stacked images within the error box of SVOM/MXT (Gotz et al., GCN 44182) or EP-FXT (Zhao et al., GCN 44186), compared to the Legacy Survey. The 3-sigma limit magnitudes are VT_B ~ 23.1 mag and VT_R ~ 23.0 mag at 31.3 minutes post trigger.

Our result is consistent with the non-detection reports from SVOM/COLIBRÍ (Antier et al., GCN 44183), MASTER (Carrasco et al., GCN 44184), Kilonova-Catcher (Freeberg et al., GCN 44185) and SVOM/C-GFT (Wu et al., GCN 44189). 

Given the early optical non-detection, near-infrared follow-up observations are encouraged.

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.