{
  "bibcode": "2013GCN.14917....1B",
  "body": "B. N. Barlow (PSU), D. N. Burrows (PSU), S. T. Holland (STScI),\nH. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC),\nD. M. Palmer (LANL), C. A. Swenson (PSU) and B.-B. Zhang (PSU) report\non behalf of the Swift Team:\n\nAt 02:21:57 UT, the Swift Burst Alert Telescope (BAT) triggered on\na likely noise fluctuation (trigger=558631).  Swift slewed immediately \nto the location.  The BAT on-board calculated location is \nRA, Dec 271.805, -22.291, which is \n   RA(J2000)  =  18h 07m 13s\n   Dec(J2000) = -22d 17' 26\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  Since it is an image trigger, the light\ncurve shows no significant features. \n\nThe XRT began observing the field at 02:29:59.5 UT, 482.3 seconds after\nthe BAT trigger. No source was detected in 376 s of promptly downlinked\ndata, which covered 39% of the BAT error circle. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 486 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 25% of\nthe BAT 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\nBAT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the large, but uncertain extinction expected. \n\nThis was a marginal significance (5.8 sigma) image peak which was\nwithin 0.2 degrees (actual distance 0.176 degrees) of a known source. \nUnder this set of conditions, Swift is programmed to slew to determine\nthe reality of the detection using the XRT and UVOT. \n\nDue to the lack of an XRT detection, and the lack of a rate trigger,\nwe believe that this is a statistical fluctuation and not a real\nsource detection. \n\n[GCN OPS NOTE(20jun13):  This Circular was delayed in distribution (~8 hrs)\nbecause none of the \"magic\" strings (eg \"GRB\", \"Swift\") was present\nin the Subject-line.]",
  "circularId": 14917,
  "createdOn": 1371725591000,
  "email": "palmer@lanl.gov",
  "subject": "Swift Trigger 558631 is not a real source",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}