TITLE: GCN CIRCULAR NUMBER: 41184 SUBJECT: GRB 250727A: AST3-2 Upper limit DATE: 25/07/28 10:02:21 GMT FROM: Tianrui Sun at Purple Mountain Obs,CAS <trsun@pmo.ac.cn> Tian-Rui Sun, Yan-Long Hua (Purple Mountain Observatory, CAS), Kun Ma, Jiali Chen, Kai-wen Zheng, Yi-Qiao Yang, Xiao-Yan Li(Nanjing Institute of Astronomical Optics & Technology, CAS), Jin-Jun Geng, Wenlong Zhang, Xue-Feng Wu (Purple Mountain Observatory, CAS), report on behalf of the AST3 Team: Following the detection of GRB 250727A by ECLAIRs onboard SVOM (Cao et al., GCN 41176), we carried out follow-up observations using the Antarctic Survey Telescope AST3-2 located at Dome A, Antarctica (Lat. −80.4173°, Long. 77.0950°). Observations began at 2025-07-27T11:09:43.449 UT. No significant optical counterpart was detected within the ECLAIRs error circle (~9 arcmin radius), compared to the Gaia DR2 catalog. The stacked image (71 × 30 s exposures) in the i-band reached a 5σ limiting magnitude of ~18.9. This non-detection is consistent with the non-detection reported by SVOM/VT (Li et al., GCN 41181). Photometric calibration was performed using the ATLAS Reference Catalog (Tonry et al. 2018). We thank Prof. Michael Ashley (UNSW) for his continuous support in the operation of AST3-2. View this GCN Circular online at https://gcn.nasa.gov/circulars/41184. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...