{
  "bibcode": "2021GCN.29857....1W",
  "body": "Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Simone Dichiara\n(GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Oc��lotl Lopez\n(UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and\nEleonora Troja (GSFC/UMD) report:\n\nWe observed the field of the Swift/BAT GRB 210421A (Moss et al., GCN Circ.\n29849) with the DDOTI wide-field imager at the Observatorio Astron��mico Nacional\non Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-21 03:05\nto 04:33 UTC (from 2.6 to 4.1 hours after the trigger) and obtained 4320 seconds\nof exposure in the w filter.\n\nWe observed a region covering aproximately 7 degrees in RA and 10 degrees in\ndeclination (about 70 square degrees), including the XRT position. We calibrated\nour images against the APASS catalog.\n\nWe do not detect any source in the XRT region to a 3-sigma limiting AB magnitude of\nw = 21.1.\n\nWe thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.",
  "circularId": 29857,
  "createdOn": 1618980960000,
  "email": "alan@astro.unam.mx",
  "subject": "GRB 210421A: DDOTI Upper Limit",
  "submitter": "Alan M Watson at UNAM  <alan@astro.unam.mx>",
  "eventId": "GRB 210421A"
}