{
  "bibcode": "2021GCN.30610....1L",
  "body": "A. Y. Lien (GSFC/UMBC), C. Gronwall (PSU), J.D. Gropp (PSU),\nN. J. Klingler (GSFC/UMBC/CRESSTII), K. L. Page (U Leicester) and\nD. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 22:57:08 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 210807C (trigger=1064421).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 143.551, -51.409 which is \n   RA(J2000) = 09h 34m 12s\n   Dec(J2000) = -51d 24' 31\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  Although the lightcurve before T+8s is\nnot currently available due to a telemetry dropout, the later lightcurve\nshows a complex structure extending at least to T+90s.  The peak count \nrate in the available lightcurve was ~800 counts/sec (15-350 keV), \nat ~20 sec after the trigger. \n\nThe XRT began observing the field at 23:00:05.5 UT, 177.1 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nuncatalogued X-ray source located at RA, Dec 143.53455, -51.40237 which\nis equivalent to:\n   RA(J2000)  = 09h 34m 08.29s\n   Dec(J2000) = -51d 24' 08.5\"\nwith an uncertainty of 7.1 arcseconds (radius, 90% containment). This\nlocation is 43 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at https://www.swift.ac.uk/sper.  We\ncannot determine whether the source is fading at the present time. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata does not constrain the column density. \n\nThe initial flux in the 2.5 s image was 2.31e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 250 seconds with the V filter starting\n180 seconds after the BAT trigger. No credible afterglow candidate has been\nfound in the initial data products. The 2.7'x2.7' sub-image covers 100% of the\nXRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The\n8'x8' region for the list of sources generated on-board covers 100% of the XRT\nerror circle. The list of sources is typically complete to about 18.0 mag. No\ncorrection has been made for the large, but uncertain, extinction expected. \n\nBurst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). \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": 30610,
  "createdOn": 1628378045000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 210807C: Swift detection of a burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 210807C"
}