{
  "bibcode": "2018GCN.22442....1L",
  "body": "A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),\nH. A. Krimm (NSF/USRA), S. J. LaPorte (PSU),\nF. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),\nD. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the\nNeil Gehrels Swift Observatory Team:\n\nAt 22:21:07 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 180224A (trigger=811561).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 202.661, +38.088 which is \n   RA(J2000)  =  13h 30m 39s\n   Dec(J2000) = +38d 05' 17\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a single FRED peak\nwith a duration of about 15 sec.  The peak count rate\nwas ~2200 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 22:22:28.1 UT, 80.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source located at RA, Dec 202.68324, 38.07881 which is equivalent\nto:\n   RA(J2000)  = 13h 30m 43.98s\n   Dec(J2000) = +38d 04' 43.7\"\nwith an uncertainty of 3.8 arcseconds (radius, 90% containment). This\nlocation is 71 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.  We\ncannot determine whether the source is fading at the present time. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 8.24\nx 10^19 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 85 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t13:30:44.09 = 202.68370\n  DEC(J2000) = +38:04:44.6  =  38.07906\nwith a 90%-confidence error radius of about 0.63 arc sec. This position is 0.9\narc sec. from the center of the XRT error circle. The estimated magnitude is\n18.94 with a 1-sigma error of about  0.15. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.01. \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/too.html.)",
  "circularId": 22442,
  "createdOn": 1519511577000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "GRB 180224A: Swift detection of a burst with an optical counterpart",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "eventId": "GRB 180224A"
}