{
  "bibcode": "2021GCN.30845....1B",
  "body": "S. D. Barthelmy (GSFC), K. L. Page (U Leicester) and\nB. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 07:58:20 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated IGR J16418-4532 (trigger=1073821).  Swift slewed immediately to the source. \nThe BAT on-board calculated location is \nRA, Dec 250.455, -45.540 which is \n   RA(J2000)  =  16h 41m 49s\n   Dec(J2000) = -45d 32' 22\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve is an image trigger\nand as such does not show any peak. \n\nThe XRT began observing the field at 08:00:28.1 UT, 128.0 seconds after\nthe BAT trigger. XRT found a bright X-ray source located at RA, Dec\n250.4669, -45.5421 which is equivalent to:\n   RA(J2000)  = 16h 41m 52.06s\n   Dec(J2000) = -45d 32' 31.6\"\nwith an uncertainty of 4.9 arcseconds (radius, 90% containment). This\nlocation is 30 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position is 15.1 arcseconds from a known X-ray\nsource: 2SXPS J164150.7-453225, also known as IGRJ16418-4532. This \nsource is in the Swift XRT 2SXPS catalogue with a mean 0.3-10 keV \ncount-rate of 0.2893 +/- 0.0028 ct/sec; see \nhttps://www.swift.ac.uk/2SXPS/2SXPS%20J164150.7-453225 for\ndetails of these previous observations. No event data are yet available\nto determine the column density using X-ray spectroscopy. \n\nUVOT took a finding chart exposure of 250 seconds with the U filter starting\n133 seconds after the BAT trigger. No credible afterglow candidate has been\nfound in the initial data products. The 2.7'x2.7' sub-image covers 100% of the\nXRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The\ncoverage of the XRT error circle by the 8'x8' region for the list of sources\ngenerated on-board is uncertain because the large number of sources filled the\navailable telemetry. The list of sources is typically complete to about 18.0\nmag. No correction has been made for the large, but uncertain, extinction\nexpected.",
  "circularId": 30845,
  "createdOn": 1631953406000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "Swift trigger 1073821: detection of IGR J16418-4532",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>"
}