TITLE:   GCN CIRCULAR
NUMBER:  43687
SUBJECT: EP260210a: SVOM/VT optical upper limit
DATE:    26/02/10 17:33:25 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

H. L. Li, Y. N. Ma, L. P. Xin, Y. L. Qiu, C. Wu,  Z. H. Yao, 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 EP260210a detected by Einstein Probe (Shi et al., GCN  43681). The observation started at 2026-02-10T10:56:57 UTC, 34.52 minutes after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. 

No uncatalogued sources are detected in single or stacked images within the error box of EP-FXT (Shi et al., GCN  43681), which is compatible with the earlier upper limits from SVOM/C-GFT (​​Kang et al., GCN 43683) and COLIBRÍ (Fortin et al, GCN 43684). The 3 sigma limit magnitudes are derived as below:

Mid time   | Band | Exposure Time | 3 sigma limit magnitude
2.316 hour   VT_B      42*50 sec      > 23.2 mag    
1.535 hour   VT_R      39*50 sec      > 22.9 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.