{
  "bibcode": "2015GCN.17712....1G",
  "body": "N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),\nA. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),\nB. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf\nof the Swift Team:\n\nAt 04:52:50 UT, the Swift Burst Alert Telescope (BAT) detected a\nmarginal significance peak in an non-rate-triggered image\n(trigger=638217). Swift slewed immediately to the location. \nThe BAT on-board calculated location is \nRA, Dec 186.582, +15.433 which is \n   RA(J2000) = 12h 26m 20s\n   Dec(J2000) = +15d 25' 58\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  As is usual with an image trigger, \nthe available BAT light curve shows no significant structure. \n\nThe XRT began observing the field at 04:55:03.4 UT, 132.9 seconds after\nthe BAT trigger. No source was detected in 147 s of promptly downlinked\ndata. We are waiting for the full dataset to detect and localise the\nXRT counterpart. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 135 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 expected extinction corresponding to E(B-V) of\n0.02. \n\nThis event triggered as part of program to follow-up marginal\nimage triggers in proximity to nearby galaxies to confirm or refute\nweak events.  In this case, the low significance (5.96 sigma),\nlack of a rate trigger, distance from the potential host galaxy\n(10 arcminutes from NGC 4421, which has a nominal diameter of 2.5 arcmin)\nand non-detection of any afterglow by XRT and UVOT implies that \nthis is a noise fluctuation in the image, and not an astrophysical source.",
  "circularId": 17712,
  "createdOn": 1429247399000,
  "email": "palmer@lanl.gov",
  "subject": "Swift Trigger 638217 is probably not an astrophysical source",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}