GCN 44074: EP260321a: SVOM/VT optical upper limit

Y. N. Ma, H. L. Li, Z. H. Yao, Y. L. Qiu, C. Wu, L. P. Xin, X. H. Han, Y. Xu, J. Wang, 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. Palmerio (CEA) report on behalf of the SVOM/VT team. 

SVOM/VT performed a Target of Opportunity observation of EP260321a detected by EP/WXT (Huang et al., GCN 44068). SVOM/VT began observing the field at 2026-03-21T13:10:39 UTC, 0.673 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. 

With X-band data available, no uncataloged source is found within the error box of FXT (Huang et al., GCN 44068) compared with DESI Legacy Survey at the mid time of 1.92 hours after trigger, VT_R > 22.8 mag with exposure time of 53*50 sec, VT_B > 23.0 mag with exposure time of 54*50 sec.
              
The stellar source and the galaxy reported by Kinder (Lee et al., GCN 44070) are detected in our observations, with no significant variability.

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.