{
  "bibcode": "2016GCN.19781....1D",
  "body": "P. D'Avanzo (INAF-OAB), J. A. Kennea (PSU),\nH. A. Krimm (CRESST/GSFC/USRA), A. Melandri (INAF-OAB),\nK. L. Page (U Leicester) and J. L. Racusin (NASA/GSFC) report on\nbehalf of the Swift Team:\n\nAt 10:58:23 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated an outburst from 4U 1850-03 (= GS1843-02; trigger=707545).  Swift slewed \nimmediately to the location.  The BAT on-board calculated location is \nRA, Dec 282.077, -2.446 which is \n   RA(J2000) = 18h 48m 18s\n   Dec(J2000) = -02d 26' 44\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  As is typical for an image trigger, \nthe BAT light curve shows no significant features. \n\nThe XRT began observing the field at 11:06:22.2 UT, 478.9 seconds after\nthe BAT trigger. Using promptly downlinked data we find an X-ray source\nwith an enhanced position: RA, Dec 282.0707, -2.4236 which is\nequivalent to:\n   RA(J2000)  = 18h 48m 16.97s\n   Dec(J2000) = -02d 25' 24.9\"\nwith an uncertainty of 2.3 arcseconds (radius, 90% containment). This\nlocation is 83 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at http://www.swift.ac.uk/sper. This\nposition is 6.9 arcseconds from a known X-ray source: 1SXPS\nJ184816.5-022522. This source is in the Swift XRT 1SXPS catalogue with\na mean 0.3-10 keV count-rate of (2.97 [+1.01, -0.85]) x 10^-3 ct/sec;\nsee http://www.swift.ac.uk/1SXPS/1SXPSJ184816.5-022522 for details of\nthese previous observations. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata does not constrain the column density. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 482 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 100% of\nthe XRT 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\nXRT 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\nNote that BAT has previously triggered on this source (GCNs 18675,\n16677,  ATel #4350). The above positions appear to be consistent with\nthe known high mass X-ray binary  4U 1850-03, and we believe the BAT\ntrigger indicates activity from this known  source.   The identifier\n1SXPSJ184816.5-022522, derived from the Swift XRT point  source\nsurvey, is most consistent with the current Swift XRT localization, \nbut it is possible this source is the same as the 4U 1850-03. \nHowever, as this  is a location 0.4 deg from the Galactic Plane, we\ncannot rule out the possibility  of a distinct Galactic source, nearby\nto 4U 1850-03.",
  "circularId": 19781,
  "createdOn": 1470483159000,
  "email": "judith.racusin@nasa.gov",
  "subject": "Swift Trigger 707545 is likely 4U 1850-03/GS1843-02",
  "submitter": "Judith Racusin at GSFC  <judith.racusin@nasa.gov>"
}