{
  "bibcode": "2021GCN.29956....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 210506A (Tohuvavohu, DeLaunay & Kennea, GCN \n29947) using the NEXT-0.6m telescope located at Nanshan, Xinjiang, \nChina. We obtained 9x300 s frames in the Sloan r-band, starting at \n15:17:27 UT on 2021-05-06, i.e., 14.63 hr after the BAT trigger.\n\nNo credible optical source is detected in our stacked image at the \nposition of the XRT source #3 that lies in the BAT error circle (ref. \nhttps://www.swift.ac.uk/ToO_GRBs/00021430/ and Evans, GCN 29949), down \nto a limiting magnitude of r~21.7, calibrated with the nearby PanSTARRS \nfield.",
  "circularId": 29956,
  "createdOn": 1620357122000,
  "email": "dxu@nao.cas.cn",
  "subject": "GRB 210506A: Nanshan/NEXT optical upper limit",
  "submitter": "Dong Xu at NAOC/CAS  <dxu@nao.cas.cn>",
  "eventId": "GRB 210506A"
}