{
  "subject": "GRB 180812A: Swift detection of a burst",
  "eventId": "GRB 180812A",
  "bibcode": "2018GCN.23129....1L",
  "createdOn": 1534063058000,
  "circularId": 23129,
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>",
  "email": "scott@milkyway.gsfc.nasa.gov",
  "body": "A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA),\nV. D'Elia (ASDC), C. Gronwall (PSU), K. L. Page (U Leicester) and\nE. Troja (NASA/GSFC/UMCP) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 08:22:30 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 180812A (trigger=852903).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 245.886, +74.670, which is \n   RA(J2000)  =  16h 23m 33s\n   Dec(J2000) = +74d 40' 11\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows several peaks\nwith a total duration of about 25 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 08:24:17.6 UT, 107.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find an uncatalogued\nX-ray source with an enhanced position: RA, Dec 245.8360, 74.6647 which\nis equivalent to:\n   RA(J2000)  = 16h 23m 20.64s\n   Dec(J2000) = +74d 39' 53.0\"\nwith an uncertainty of 2.7 arcseconds (radius, 90% containment). This\nlocation is 51 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 in excess of the Galactic value (4.37 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.8\n(+4.29/-3.49) x 10^21 cm^-2 (90% confidence). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 112 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\n0.04. \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.)"
}