{
  "bibcode": "2021GCN.29619....1D",
  "body": "V. D'Elia (SSDC), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC),\nA. D'Ai (INAF-IASFPA), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),\nK. L. Page (U Leicester), T. Sakamoto (AGU), M. H. Siegel (PSU) and\nA. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 06:37:56 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 210308A (trigger=1036227).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 67.088, +37.411 which is \n   RA(J2000)  =  04h 28m 21s\n   Dec(J2000) = +37d 24' 39\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a few overlapping peaks\nwith a duration of about 15 sec.  The peak count rate\nwas ~6000 counts/sec (15-350 keV), at ~3 sec after the trigger. \n\nThe XRT began observing the field at 06:39:21.81 UT, 85.0 seconds after\nthe BAT trigger. Using promptly downlinked data we find an\nuncatalogued X-ray source with a position: RA, Dec 67.076417, \n37.435310 which is equivalent to:\n   RA(J2000)  = 04h 28m 18.34s\n   Dec(J2000) = +37d 26' 07.11\"\nwith an uncertainty of 4.3 arcseconds (radius, 90% containment). This\nlocation is 94 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 http://www.swift.ac.uk/sper. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 94 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t04:28:17.73 =  67.07388\n  DEC(J2000) = +37:26:02.0  =  37.43388\nwith a 90%-confidence error radius of about 0.63 arc sec. This position is 8.5\narc sec. from the center of the XRT error circle. The estimated magnitude is\n18.57 with a 1-sigma error of about  0.15. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 1.295. \n\nBurst Advocate for this burst is V. D'Elia (valerio.delia AT ssdc.asi.it). \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": 29619,
  "createdOn": 1615186161000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 210308A: Swift detection of a burst with an optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 210308A"
}