{
  "bibcode": "2021GCN.29420....1L",
  "body": "A. Y. Lien (GSFC/UMBC), E. Ambrosi (INAF-IASFPA),\nS. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC),\nJ.D. Gropp (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),\nS. Laha (GSFC/UMBC/CRESST), F. E. Marshall (NASA/GSFC),\nD. M. Palmer (LANL), A. Tohuvavohu (U Toronto) and\nE. Troja (NASA/GSFC/UMCP) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 21:52:08 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 210207B (trigger=1031297).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 270.582, +53.694 which is \n   RA(J2000) = 18h 02m 20s\n   Dec(J2000) = +53d 41' 39\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a multi-peaked\nstructure with a duration of about 100 sec.  The peak count rate\nwas ~2500 counts/sec (15-350 keV), at ~45 sec after the trigger. \n\nThe XRT began observing the field at 21:53:22.0 UT, 73.9 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 270.6356, 53.6836 which is equivalent to:\n   RA(J2000)  = 18h 02m 32.54s\n   Dec(J2000) = +53d 41' 01.0\"\nwith an uncertainty of 4.7 arcseconds (radius, 90% containment). This\nlocation is 120 arcseconds from the BAT onboard position, within the\nBAT error circle. No event data are yet available to determine the\ncolumn density using X-ray spectroscopy. \n\nThe initial flux in the 2.5 s image was 1.09e-08 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 82 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t18:02:32.40 = 270.63501\n  DEC(J2000) = +53:40:56.0  =  53.68223\nwith a 90%-confidence error radius of about 0.74 arc sec. This position is 5.1\narc sec. from the center of the XRT error circle. The estimated magnitude is\n13.72 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.041. \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": 29420,
  "createdOn": 1612735409000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 210207B: Swift detection of a burst with a bright optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 210207B"
}