{
  "bibcode": "2020GCN.29118....1X",
  "body": "D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), S.Y. Fu, X. Liu (NAOC), X. Gao \n(Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:\n\nWe observed the field of GRB 201221D (Page et al., GCN 29112) using the \nNEXT-0.6m optical telescope located at Nanshan, Xinjiang, China. \nObservations automatically started at 23:07:39 UT on 2020-12-21, i.e., \n65 s after the BAT trigger. We obtained 3x40s, 4x60s and 12x90s frames \nin the Sloan r-filter.\n\nNo optical source is detected in our stacked image at the XRT enhanced \nposition (Evans et al., GCN 29113), down to a upper limit of r~21.3, \ncalibrated with the nearby PanSTARRS field.",
  "circularId": 29118,
  "createdOn": 1608601112000,
  "email": "dxu@nao.cas.cn",
  "subject": "GRB 201221D: Nanshan/NEXT early optical upper limit",
  "submitter": "Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>",
  "eventId": "GRB 201221D"
}