GRB 241209B: SVOM/VT optical continuous fading

SVOM/VT revisited GRB 241209B（Xie et al., GCN 38478）since 2024-12-10T15:07:15 UT with a total exposure time of 8750 seconds. The optical counterpart (Qiu et al. GCN 38516) was continuously fading, reaching a magnitude of 23.70 +/-0.30 in VT_R at ~38.55 hours post trigger (mid-time). Nothing was seen down to limiting magnitude of 23.80 (3 sigma) in simultaneous channel VT_B. 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.