{
  "bibcode": "2017GCN.21450....1G",
  "body": "S. L. Gibson (U Leicester), D. N. Burrows (PSU), J. A. Kennea (PSU),\nS. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester),\nD. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the\nSwift Team:\n\nAt 22:01:41 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 170810A (trigger=767284).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 187.950, +3.647 which is \n   RA(J2000) = 12h 31m 48s\n   Dec(J2000) = +03d 38' 48\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex\nstructure with a duration of 160 sec. The peak count rate \nwas ~2600 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 22:02:57.5 UT, 76.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source with an enhanced position: RA, Dec\n187.9389, 3.6603 which is equivalent to:\n   RA(J2000)  = 12h 31m 45.33s\n   Dec(J2000) = +03d 39' 37.0\"\nwith an uncertainty of 2.1 arcseconds (radius, 90% containment). This\nlocation is 62 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 (2.23 x\n10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.2\n(+1.98/-1.79) x 10^21 cm^-2 (90% confidence). \n\nThe initial flux in the 2.5 s image was 4.45e-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 876 seconds after the BAT trigger. There is a candidate afterglow in\nthe list of sources generated on-board at\n  RA(J2000)  =\t12:31:45.31 = 187.93881\n  DEC(J2000) = +03:39:38.9  =\t3.66080\nwith a 90%-confidence error radius of about 1.10 arc sec. This position is 3.5\narc sec. from the center of the XRT error circle. The estimated magnitude is\n17.87. No correction has been made for the expected extinction corresponding to\nE(B-V) of 0.03. \n\nAn earlier UVOT finding chart exposure, starting 85 seconds after the \nBAT trigger, showed that the counterpart was much brighter at that time. \nHowever, this brightness precluded automatic analysis.  \nResults for this early bright detection will be presented later. \n\nThe original GCN notice of this burst suggested an association with the\ngalaxy NGC4496A.  However, the apparent separation from this galaxy,\n0.295 deg, implies that these two objects are not related. \n\nBurst Advocate for this burst is S. L. Gibson (slg44 AT le.ac.uk). \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": 21450,
  "createdOn": 1502404781000,
  "email": "palmer@lanl.gov",
  "subject": "GRB 170810A: Swift detection of a burst with a bright optical counterpart",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>",
  "eventId": "GRB 170810A"
}