{
  "bibcode": "2005GCN..3082....1B",
  "body": "S. Barthelmy (GSFC), D.Burrows (PSU), L. Barbier (GSFC), J. Cummings \n(GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD), \nJ. Kennea (PSU), H. Krimm (GSFC/USRA), D. Malesani (SISSA), C. Markwardt \n(GSFC/UMD), A. Moretti (INAF-OAB), K. Page (U. Leicester), D. Palmer \n(LANL), A. Parsons (GSFC), P. Romano (INAF-OAB), T. Sakamoto (GSFC), G. \nSato (ISAS), M. Suzuki (Saitama), J. Tueller (GSFC)\non behalf of the Swift-BAT/-XRT teams:\n\nFurther analysis of Swift data on BAT trigger #107873 has led to an \nambiguous situation regarding the reality of this marginal BAT trigger.\n\nThe Swift-BAT triggered (#107873) at 10:43:21 UT.  The trigger occurred on \nthe rising edge of the SAA.  Ground analysis has confirmed the very low \nimage-domain detection significance of this trigger.  A visual inspection \nof the mask-tagged light curve also shows very marginal emission.\nAs a result, a retraction GCN Notice was issued earlier today.  We are now\nammending that Notice.\n\nThe BAT position was within the Swift Earth limb constraint at the time of \nthe burst, so Swift did not execute a prompt automated slew.  The spacecraft \nexecuted a delayed slew to the BAT location at about 11:33 UT and XRT \nobservations began at 11:35:54 UT.  Two orbits of data were collected by \nthe XRT, for a total of 4157s of exposure.  Preliminary analysis indicates \nthat there are four X-ray sources in the XRT field of view, two of which \nfall inside the BAT error circle.  These are:\n\nSource #1: RA(J2000) = 12 10 29.1, Dec(J2000) = +77 37 04.8. This is a very \nweak source (about 0.006 cps).  It appears to be roughly constant in \nintensity, but the source is so faint that we cannot determine with \nconfidence whether or not it is varying in flux.\n\nSource #2: RA(J2000) = 12 09 37.2, Dec(J2000) = +77 35 56.5.  This source\nis brighter (about 0.01 cps) and may be fading.  Again, we cannot be certain \nwith the data currently in hand.\n\nThe other two sources are a bright star and a very faint object well \noutside the BAT error circle.  The estimated uncertainty in the XRT \npositions is 6 arcseconds radius.\n\nA 20 ks Target of Opportunity observation has been initiated to provide a \nsecond set of data beginning at about 19:45 UT.  This should help us \ndetermine the likelihood that either XRT source is related to the BAT trigger.\n\nIn light of these XRT observations, the BAT team cannot rule out the \npossibility that this trigger represents a threshold-level GRB.",
  "circularId": 3082,
  "createdOn": 1110409772000,
  "email": "Scott@lheamail.gsfc.nasa.gov",
  "subject": "Swift-BAT trigger 107873 (GRB050309): possible X-ray counterparts",
  "submitter": "Scott Barthelmy at NASA/GSFC  <Scott@lheamail.gsfc.nasa.gov>",
  "eventId": "GRB 050309"
}