{
  "bibcode": "2019GCN.23900....1B",
  "body": "A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),\nK. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU) and\nM. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 08:54:09 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated Swift J1858.6-0814 (trigger=889483).  Swift slewed immediately \nto the source. The BAT on-board calculated location is \nRA, Dec 284.640, -8.235 which is \n   RA(J2000) = 18h 58m 34s\n   Dec(J2000) = -08d 14' 05\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty). As is usual for an image trigger, there is\nno obvious variation in the immediately-available BAT lightcurve. \n\nThe XRT began observing the field at 09:03:09.4 UT, 539.9 seconds after\nthe BAT trigger. Using promptly downlinked data we find an \nX-ray source located at RA, Dec 284.64412, -8.23735 which is equivalent\nto:\n   RA(J2000)  = 18h 58m 34.59s\n   Dec(J2000) = -08d 14' 14.5\"\nwith an uncertainty of 3.7 arcseconds (radius, 90% containment). This\nlocation is 16 arcseconds from the BAT onboard position, within the BAT\nerror circle. This localisation is consistent with the previously \nreported position (ATel 12160).  \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 3.21\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 543 seconds after the BAT trigger. There is a source in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t18:58:34.91 = 284.64544\n  DEC(J2000) = -08:14:14.8  =  -8.23745\nwith a 90%-confidence error radius of about 0.61 arc sec. This position is 5.5\narc sec. from the center of the XRT error circle. The estimated magnitude is\n16.34 with a 1-sigma error of about  0.14. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.26. \n\nThis source was originally discovered by Swift-BAT in the transient\nmonitor (ATel 12151), and Swift triggered on this source on 2018 Nov\n23 (GCN 23431). The source  has just emerged from behind the Sun, and\nNuSTAR have shown it still  to be active in X-rays (ATel 12512). The\nBAT transient monitor page  for this source is available at \nhttps://swift.gsfc.nasa.gov/results/transients/weak/SWIFTJ1858.6-0814/",
  "circularId": 23900,
  "createdOn": 1550482822000,
  "email": "klp5@leicester.ac.uk",
  "subject": "Trigger 889483: Swift detection of Swift J1858.6-0814",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>"
}