{
  "bibcode": "2020GCN.28250....1B",
  "body": "M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),\nA. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),\nA. Melandri (INAF-OAB), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB)\nand K. K. Simpson (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 04:07:22 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated on an image peak that is likely due to a noisy detector element\n(trigger=989458).  Swift slewed immediately to the event. \nThe BAT on-board calculated location is \nRA, Dec 202.461, -22.590 which is \n   RA(J2000) = 13h 29m 51s\n   Dec(J2000) = -22d 35' 22\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve is difficult to interpret\ndue to the presence of the noisy detector element.  The full downlinked\ndata will allow the noisy element to be removed from analysis. \n\nThe XRT began observing the field at 04:08:57.6 UT, 95.3 seconds after\nthe BAT trigger. No source was detected in 323 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 98 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 ~10% 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\n0.10. \n\nDue to the lack of detection in XRT, the marginal significance of\nthe BAT detection (6.58 sigma in the on-board analysis, dropping\nto 6.3 sigma in ground analysis of the scaled detector map)\nand the presence of hot detector pixels in the imaged data,\nwe believe that this is probably not an astrophysical event. \n\nFinal determination of the status of this trigger awaits\nthe full downloaded data set.",
  "circularId": 28250,
  "createdOn": 1597552212000,
  "email": "palmer@lanl.gov",
  "subject": "Swift trigger 989458 is likely not an astrophysical source",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}