{
  "bibcode": "2016GCN.19514....1B",
  "body": "S. D. Barthelmy (GSFC), D. M. Palmer (LANL), T. G. R. Roegiers (PSU)\nand M. H. Siegel (PSU) report on behalf of the Swift Team:\n\nAt 02:21:03 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated a possible new source (trigger=689956).  Swift did not immediately\nslew to the source due to its low merit value. \nThe BAT on-board calculated location is \nRA, Dec 266.422, -29.008, which is \n   RA(J2000)  =  17h 45m 41s\n   Dec(J2000) = -29d 00' 29\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  As is typical for image triggers (especially\nlong triggers such as this 15 min one), the real-time TDRSS\ndata does not show anything significant. \n\nThe XRT began observing the field at 02:56:14.5 UT, 2110.9 seconds\nafter the BAT trigger. Using promptly downlinked data we find an X-ray\nsource located at RA, Dec 266.41879, -29.01122 which is equivalent to:\n   RA(J2000)  = 17h 45m 40.51s\n   Dec(J2000) = -29d 00' 40.4\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nposition may be improved as more data are received; the latest position\nis available at http://www.swift.ac.uk/sper. This position is 2.2\narcseconds from that of a known X-ray source: 1BMC 174540.6-290039 in\nthe CHANDRA BMWCHANCAT catalogue\n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata does not constrain the column density. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 2113 seconds after the BAT trigger. No credible afterglow candidate\nhas been found in the initial data products. The 2.7'x2.7' sub-image covers\n100% of the XRT error circle. The typical 3-sigma upper limit has been about\n19.6 mag. The 8'x8' region for the list of sources generated on-board covers\n100% of the XRT error circle. The list of sources is typically complete to\nabout 18 mag. No correction has been made for the large, but uncertain\nextinction expected. \n\nThis source is presumably the same as the source that triggered \n2.5 days earlier (Barthelmy et al. GCN 19499).  This may\nbe the recently-detected source SWIFT J174540.2-290037 which\nhas continued to brighten in the XRT during routine monitoring\n(Degenaar et al. Atel #9109), the previously detected and currently-\nactive SWIFT J174540.7-290015 (Reynolds et al; ATel #8649) or some\nother source such as 1BMC 174540.6-290039, located by XRT in\nthe initial exposure. Due to the crowded field this close to the\nGalactic center (~4 arcminutes) we cannot definitively determine \nwhich source produced either trigger with the currently-available data.",
  "circularId": 19514,
  "createdOn": 1465442150000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "Trigger 689956: Swift detection of a source near the Galactic center",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>"
}