TITLE:   GCN CIRCULAR
NUMBER:  45671
SUBJECT: EP260920b: SVOM/VT optical observation
DATE:    26/09/21 07:46:45 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

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

SVOM/VT performed ToO observation on the field of EP260920b (Ni et al., GCN 45664; Yang et al., GCN 45670). The observation started at 2026-09-21T01:24:03 UTC, about 11.3 hr after trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.

The optical counterpart (Liu et al., GCN 45668; García-García et al., GCN 45669) was detected in VT stacked images of both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:

Mid time | Band | Exposure Time |  Magnitude (AB)
12.14 hr   VT_B     55*50 sec      22.3 +/- 0.2
12.14 hr   VT_R     48*50 sec      21.5 +/- 0.1 

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.