{
  "bibcode": "2020GCN.27746....1G",
  "body": "C. Gronwall (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU),\nS. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC),\nF. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and\nD. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 15:03:28 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated a burst from Soft Gamma Repeater SGR Swift J1818.0-1607 \n(trigger=972614).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 274.550, -16.193 which is \n   RA(J2000) = 18h 18m 12s\n   Dec(J2000) = -16d 11' 32\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single peak\nstructure with a duration of about 100 ms.  The peak count rate\nwas ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger. \n\nThe XRT began observing the field at 15:04:27.5 UT, 59.0 seconds after\nthe BAT trigger. Using promptly downlinked data we find an \nX-ray source with an enhanced position: RA, Dec 274.5010, -16.1314\nwhich is equivalent to:\n   RA(J2000)  = 18h 18m 00.23s\n   Dec(J2000) = -16d 07' 53.0\"\nwith an uncertainty of 3.0 arcseconds (radius, 90% containment). This\nlocation is 279 arcseconds from the BAT onboard position, consistent \nwith the known position of Swift J1818.0-1607. This position\nmay be improved as more data are received; the latest position is\navailable at https://www.swift.ac.uk/sper.  We cannot determine whether\nthe 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 consistent with the Galactic value of 1.35\nx 10^22 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 62 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 none of\nthe XRT error circle. The 8'x8' region for the list of sources generated\non-board covers none of the XRT error circle. No correction has been made for\nthe large, but uncertain, extinction expected. \n\nSwift is currently monitoring this source every 3 days under a ToO program.",
  "circularId": 27746,
  "createdOn": 1589642475000,
  "email": "palmer@lanl.gov",
  "subject": "Swift Detection of a burst from SGR Swift J1818.0-1607",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}