{
  "bibcode": "2018GCN.23146....1M",
  "body": "F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),\nD. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the\nNeil Gehrels Swift Observatory Team:\n\nAt 03:12:04 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 180818A (trigger=853824).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 169.611, -48.344 which is \n   RA(J2000) = 11h 18m 27s\n   Dec(J2000) = -48d 20' 39\"\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 10 sec.  The peak count rate\nwas ~800 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 03:13:18.0 UT, 74.0 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source with an enhanced position: RA, Dec\n169.6364, -48.3444 which is equivalent to:\n   RA(J2000)  = 11h 18m 32.73s\n   Dec(J2000) = -48d 20' 39.7\"\nwith an uncertainty of 2.4 arcseconds (radius, 90% containment). This\nlocation is 60 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\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density in excess of the Galactic value (1.14 x\n10^21 cm^-2, Willingale et al. 2013), with an excess column of 8.5\n(+7.18/-5.58) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 1.28e-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 82 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 100% of\nthe XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. \nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.11. \n\nBurst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.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": 23146,
  "createdOn": 1534562743000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 180818A: Swift detection of a burst",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 180818A"
}