{
  "bibcode": "2020GCN.28278....1D",
  "body": "S. Dichiara (NASA/GSFC/UMCP), S. D. Barthelmy (GSFC),\nD. N. Burrows (PSU), P. A. Evans (U Leicester), C. Gronwall (PSU),\nJ.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),\nN. P. M. Kuin (UCL-MSSL), S. Laha (GSFC/UMBC/CRESST),\nK. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)\nreport on behalf of the Neil Gehrels Swift Observatory Team:\n\nAt 13:15:05 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated a possible GRB 200821A (trigger=992444).  Swift slewed \nimmediately to the location. \nThe BAT on-board calculated location is \nRA, Dec 353.570, -48.277 which is \n   RA(J2000) = 23h 34m 17s\n   Dec(J2000) = -48d 16' 37\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a sequence of\nshort peaks covering about 20 seconds.  The peak count rate\nwas ~1200 counts/sec (15-350 keV), at ~9 sec after the trigger. \n\nThe XRT began observing the field at 13:17:33.3 UT, 147.9 seconds after\nthe BAT trigger. No source was detected in 1.3 ks of promptly\ndownlinked data. We are waiting for the full dataset to detect and\nlocalise the XRT counterpart. \n\nUVOT took a finding chart exposure of 250 seconds with the U filter\nstarting  310 seconds after the BAT trigger. There is a candidate\nafterglow in the  rapidly available 2.7'x2.7' sub-image at \n  RA(J2000)  =\t23:34:24.51 = 353.60212 \n  DEC(J2000) = -48:16:28.4  = -48.27456  with a 90%-confidence error\nradius of about 0.83 arc sec. This position is 77.5  arc sec. from the\ncenter of the BAT error circle. The estimated magnitude is  19.92 with\na 1-sigma error of about  0.23. No correction has been made for the \nexpected extinction corresponding to E(B-V) of 0.01.  We note there is\na known faint source at this position in the DSS. \n\nThis source lies within the current (Sector 28) field-of-view of TESS camera 2. \n\nThis event has a highly unusual lightcurve for a GRB in BAT. \nThe XRT data is dominated by a single hot pixel, which is preventing\nrapid analysis of the data to find a counterpart.  The UVOT\ndetection may be due to the known DSS source. \n\nFor these reasons we cannot confidently say whether this is an instrumental\nartifact or an astrophysical source.  Further analysis will require the\ndownlinked data set. \n\nBurst Advocate for this burst is S. Dichiara (dichiara AT umd.edu). \nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/)",
  "circularId": 28278,
  "createdOn": 1598018665000,
  "email": "palmer@lanl.gov",
  "subject": "Swift Trigger 992444: a possible GRB 200821A",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 200821A"
}