{
  "bibcode": "2021GCN.30669....1F",
  "body": "S.Y. Fu (NAOC), Z.P. Zhu (NAOC,HUST), X. Liu, D. Xu (NAOC), X. Gao \n(Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:\n\nWe observed the field of GRB 210820A (Beardmore et al., GCN 30664) using \nthe NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We obtained \n10x200 s frames in the Sloan r-band, starting at 21:17:58 UT on \n2021-08-20, i.e., 3.67 hr after the BAT trigger.\n\nNo optical source is detected in our stacked image at the Swift/UVOT \nposition (Beardmore et al., GCN 30664), down to a limiting magnitude of \nr~21.3, calibrated with the nearby PanSTARRS field.",
  "circularId": 30669,
  "createdOn": 1629518470000,
  "email": "dxu@nao.cas.cn",
  "subject": "GRB 210820A: Nanshan/NEXT optical upper limit",
  "submitter": "Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>",
  "eventId": "GRB 210820A"
}