GRB 240828B: GWAC-F50A optical upper limit

We began to observe GRB 240828B (Le Provost et al., GCN 37318) detected by SVOM/ECLAIRs, with GWAC-F50A telescope at Xinglong station,China,at 16:45:50(UT), August 28,2024, about 3.55 hours after the burst. The weather was not good. After stacking 20*100 seconds, no any new sources were detected in our stacked image within the X-ray afterglow error circles (Page et al. GCN 37334) down to a limit magnitude of 18.5 mag in R band at the mid-time of 3.83 hours post the burst, calibrated to several nearby USNO B1.0 stars. We acknowledge the excellent support from observation assistant Yangtong Zheng and Winlong Dong.