GCN 44038: EP260316a / GRB 260316A: SVOM/VT optical upper limits

2026-03-17T15:21:28.386Z | rev 0 | event: GRB 260316A
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) report on behalf of the SVOM/VT team.

SVOM/VT performed ToO observation of the field of EP260316a detected by Einstein Probe (Jiang et al., GCN 44027, GCN 44034), and GRB 260316A with the sub-threshold detection by Fermi (Ravasio et al., GCN 44029). The observation started at 2026-03-16T22:31:53 UTC, i.e., about 9.98 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.

No uncatalogued optical source was detected in our stacked images. The 3-sigma upper limits are:

Mid_time         Band        Exposure Time     Magnitude (AB) 
10.35 hour       VT_R           37*70 sec       > 23.2  mag
10.35 hour       VT_B           39*70 sec       > 23.3  mag

The faint optical candidate reported by COLIBRÍ (Fortin et al., GCN 44037) was not detected in our stacked images.

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.