TITLE:   GCN CIRCULAR
NUMBER:  29934
SUBJECT: GRB 210504A: AST3-3 YaoAn Optical Upper Limit
DATE:    21/05/04 22:44:24 GMT
FROM:    Tianrui Sun at Purple Mountain Obs,CAS  <trsun@pmo.ac.cn>

Tianrui Sun(Purple Mountain Observatory), Lei Hu, Maokai Hu, Xuefeng Wu, Lei Liu, Kelai Meng, Xiaoyan Li(Nanjing Institute of Astronomical Observation Technology), Zhengyang Li, Xiangyan Yuan, Lifan Wang(TAMU), Xiaofeng Wang (Tsinghua University), report on behalf the AST3 Team:


Following the detection of GRB 210504A by Swift (Beardmore et al. GCNC 29929), we use Antarctic Survey Telescope 3-3 at YaoAn Astronomy Observation (China, Yunnan) for follow-up. Our observation started on 2021-05-04T16:02:29.850 (about 2 hours after the trigger of BAT, according to Lien et al. GCNC 29930). No optical source was detected within the XRT error box down to 21.0 +/- 0.6 mag in the coadded image (total 2100s, g-band). Our non-detection result is consistent with the UVOT (Beardmore et al. GCNC 29929), MASTER (Lipunov et al. GCNC 29931), and the BOOTES-4/ MET (Hu et al. GCNC 29932) limits.