{
  "bibcode": "2015GCN.17686....1M",
  "body": "D. Malesani (DARK/NBI), D. M. Palmer (LANL) and T. N. Ukwatta (LANL)\nreport on behalf of the Swift Team:\n\nAt 19:36:25 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated a burst from SAX J1808.4-3658 (trigger=637765).  Swift slewed\nimmediately to the burst.  The BAT on-board calculated location is \nRA, Dec 272.073, -36.974 which is \n   RA(J2000) = 18h 08m 18s\n   Dec(J2000) = -36d 58' 27\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a double-peaked\nstructure with a duration of about 20 sec.  The peak count rate\nwas ~2400 counts/sec (15-350 keV), at ~6 sec after the trigger. \n\nThe XRT began observing the field at 19:37:11.2 UT, 46.1 seconds after\nthe BAT trigger. XRT found a bright X-ray source located at RA, Dec\n272.1135, -36.9774 which is equivalent to:\n   RA(J2000)  = +18h 08m 27.24s\n   Dec(J2000) = -36d 58' 38.6\"\nwith an uncertainty of 4.8 arcseconds (radius, 90% containment). This\nlocation is 117 arcseconds from the BAT onboard position, within the\nBAT error circle. This position is 6.7 arcseconds from a known X-ray\nsource: SAX J1808.4-3658. This source is in the Swift XRT 1SXPS\ncatalogue with a mean 0.3-10 keV count-rate of 0.3550 +/- 0.0038\nct/sec; see http://www.swift.ac.uk/1SXPS/1SXPSJ180827.6-365843 for\ndetails of these previous observations. No event data are yet available\nto determine the column density using X-ray spectroscopy. \n\nThe initial flux in the 2.5 s image was 6.62e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 54 seconds after the BAT trigger. The source is clearly visible\nin the UVOT image, but the crowded field prevents automatic estimation\nof its brightness at this time. \n\nThis source is currently in outburst (Sanna et al., ATel 7364). \nIts BAT lightcurve is given at\nhttp://swift.gsfc.nasa.gov/results/transients/weak/SAXJ1808.4-3658/",
  "circularId": 17686,
  "createdOn": 1428782248000,
  "email": "palmer@lanl.gov",
  "subject": "Swift detection of SAX J1808.4-3658",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}