{
  "bibcode": "2012GCN.13982....1H",
  "body": "E. A. Helder (PSU), S. D. Barthelmy (GSFC), V. D'Elia (ASDC),\nP. A. Evans (U Leicester), F. E. Marshall (NASA/GSFC),\nC. J. Mountford (U Leicester), K. L. Page (U Leicester) and\nD. M. Palmer (LANL) report on behalf of the Swift Team:\n\nAt 10:02:41 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 121123A (trigger=539358).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 307.362, -11.860 which is \n   RA(J2000)  =  20h 29m 27s\n   Dec(J2000) = -11d 51' 34\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a single peak\nstructure with a duration of about 25 sec.  The peak count rate\nwas ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 10:04:44.3 UT, 123.0 seconds after\nthe BAT trigger. XRT found a bright, uncatalogued X-ray source located\nat RA, Dec 307.3179, -11.8590 which is equivalent to:\n   RA(J2000)  = +20h 29m 16.30s\n   Dec(J2000) = -11d 51' 32.4\"\nwith an uncertainty of 5.4 arcseconds (radius, 90% containment). This\nlocation is 155 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 1.30e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 131 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t20:29:16.31 = 307.31794\n  DEC(J2000) = -11:51:35.4  = -11.85983\nwith a 90%-confidence error radius of about 0.67 arc sec. This position is 3.0\narc sec. from the center of the XRT error circle. The estimated magnitude is\n19.34 with a 1-sigma error of about  0.17. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.05. \n\nBurst Advocate for this burst is E. A. Helder (helder AT psu.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/too.html.)",
  "circularId": 13982,
  "createdOn": 1353665879000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 121123A: Swift detection of a burst with optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 121123A"
}