{
  "bibcode": "2018GCN.23425....1D",
  "body": "A. D'Ai (INAF-IASFPA), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),\nM. J. Moss (George Washington University), B. Sbarufatti (PSU) and\nA. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 17:33:34 UT, the Swift Burst Alert Telescope (BAT) triggered \non count rate rise near the SAA passage and produced an image with \na marginal-significance peak of 6.55 sigma (trigger=872470).  \nSwift slewed immediately to the event. \nThe BAT on-board calculated location is \nRA, Dec 299.270, -15.665 which is \n   RA(J2000) = 19h 57m 05s\n   Dec(J2000) = -15d 39' 54\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).   The BAT light curve shows a gradual rise and \ndecrease of high background count rate due to the SAA, but \nno obvious peak at the trigger time. \n\nThe XRT began observing the field at 17:37:56.5 UT, 262.2 seconds after\nthe BAT trigger. No source was detected in 451 s of promptly downlinked\ndata, which covered 94% of the BAT error circle. We are waiting for the\nfull dataset to detect and localise the XRT counterpart. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 1073 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 25%\nof the BAT error circle. The typical 3-sigma upper limit has been about 19.6\nmag. The 8'x8' region for the list of sources generated on-board covers 100% of\nthe BAT error circle. The list of sources is typically complete to about 18\nmag. No correction has been made for the expected extinction corresponding to\nE(B-V) of 0.16. \n\nDue to the lack of a clear peak in the BAT lightcurve, the\nmarginal (6.55 sigma) BAT image peak, and the lack of an\nXRT counterpart, we believe that this event was due to particle\nbackground near the SAA and is not an astrophysical event. \n\nFurther analysis will require the full downlinked dataset.",
  "circularId": 23425,
  "createdOn": 1542564274000,
  "email": "amy.y.lien@nasa.gov",
  "subject": "Swift Trigger 872470 is probably not a GRB",
  "submitter": "Amy Lien at GSFC  <amy.y.lien@nasa.gov>"
}