{
  "bibcode": "2021GCN.30568....1T",
  "body": "E. Troja (NASA/GSFC/UMCP), E. Ambrosi (INAF-IASFPA),\nV. D'Elia (SSDC & INAF-OAR), A. Y. Lien (GSFC/UMBC),\nF. E. Marshall (NASA/GSFC), B. Sbarufatti (PSU) and\nA. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 22:21:08 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 210731A (trigger=1062336).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 300.314, -28.042 which is \n   RA(J2000) = 20h 01m 15s\n   Dec(J2000) = -28d 02' 30\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex\nstructure with a duration of about 40 sec.  The peak count rate\nwas ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 22:24:29.4 UT, 200.9 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 300.3036, -28.0595 which is equivalent to:\n   RA(J2000)  = 20h 01m 12.86s\n   Dec(J2000) = -28d 03' 34.2\"\nwith an uncertainty of 5.8 arcseconds (radius, 90% containment). No\nevent data are yet available to determine the column density using\nX-ray spectroscopy. \n\nThe initial flux in the 2.5 s image was 7.96e-10 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of  63 seconds with the White filter\nstarting 210 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 100% of\nthe XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. \nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.092. \n\nBurst Advocate for this burst is E. Troja (eleonora.troja 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": 30568,
  "createdOn": 1627770882000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 210731A: Swift detection of a burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 210731A"
}