TITLE:   GCN CIRCULAR
NUMBER:  44224
SUBJECT: EP260405a: SVOM/VT optical upper limits
DATE:    26/04/06 08:56:31 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

H. L. Li, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu, L. P. Xin, 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) report on behalf of the SVOM/VT team.

SVOM/VT performed ToO observations to the fast X-ray transient EP260405a triggered by Einstein Probe (Li et al., GCN 44222). The observation started at 2026-04-05T11:28:35 UTC, approximately 7.70 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. 

No uncatalogued sources were detected within the error box of EP-WXT (Li et al., GCN 44222), compared to the Legacy Survey. The measurements in AB magnitude are as follows:

Mid time  |  Band   | Exposure Time | 3 sigma upper limit
8.86 hr      VT_B       107*50 sec         > 23.7 mag    
8.86 hr      VT_R       105*50 sec         > 23.6 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.