TITLE:   GCN CIRCULAR
NUMBER:  44244
SUBJECT: EP260409a: SVOM/VT optical upper limits
DATE:    26/04/09 09:55:42 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

H. L. Li, C. Wu, L. P. Xin, Y. L. Qiu, 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, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.

SVOM/VT performed ToO observations of EP260409a triggered by Einstein Probe (Jiang et al., GCN 44240). The observation started at 2026-04-09T01:35:09 UTC, approximately 1.28 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 (Jiang et al., GCN 44240), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:

Mid time  |  Band   | Exposure Time | 3 sigma upper limit
3.04 hr      VT_B       106*50 sec         > 23.7 mag    
3.04 hr      VT_R       101*50 sec         > 23.6 mag

Our non-detection is consistent with the result from COLIBRÍ (Globus et al., GCN 44243).

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.