{
  "bibcode": "2021GCN.30960....1D",
  "body": "S. Dichiara (NASA/GSFC/UMCP), J.D. Gropp (PSU), J. A. Kennea (PSU),\nH. A. Krimm (NSF), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),\nF. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),\nD. M. Palmer (LANL), B. Sbarufatti (PSU), M. H. Siegel (PSU) and\nA. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 21:05:52 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 211023B (trigger=1080859).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 170.302, +39.137 which is \n   RA(J2000) = 11h 21m 12s\n   Dec(J2000) = +39d 08' 14\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single-peaked\nstructure with a duration of about 2 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 21:07:27.3 UT, 95.3 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 170.31048, 39.13595 which is equivalent\nto:\n   RA(J2000)  = 11h 21m 14.52s\n   Dec(J2000) = +39d 08' 09.4\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nlocation is 23 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. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density in excess of the Galactic value (2.30 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5\n(+2.51/-2.21) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 97 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t11:21:14.31 = 170.30963\n  DEC(J2000) = +39:08:08.8  =  39.13578\nwith a 90%-confidence error radius of about 0.79 arc sec. This position is 3.2\narc sec. from the center of the XRT error circle. The estimated magnitude is\n19.32 with a 1-sigma error of about  0.16. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.024. \n\nWe note that this is Swift's 1500th GRB. \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": 30960,
  "createdOn": 1635023819000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 211023B: Swift detection of a possibly short burst with an optical counterpart",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 211023B"
}