{
  "bibcode": "2014GCN.17068....1B",
  "body": "S. D. Barthelmy (GSFC), M. M. Chester (PSU), C. Gronwall (PSU),\nT. Sakamoto (AGU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of\nthe Swift Team:\n\nAt 21:11:12 UT, the Swift Burst Alert Telescope (BAT) triggered on\nVela X-1 (trigger=618634).  Swift slewed immediately to the source. \nThe BAT on-board calculated location is \nRA, Dec 135.536, -40.534, which is \n   RA(J2000)  =  09h 02m 09s\n   Dec(J2000) = -40d 32' 02\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve shows a cluster of peaks\nwith a duration of about 40 sec.  The peak count rate\nwas ~500 counts/sec (15-350 keV), at ~1 sec after the trigger. \n\nThe XRT began observing the field at 21:13:29.8 UT, 137.6 seconds after\nthe BAT trigger. XRT found a bright X-ray source located at RA, Dec\n135.5254, -40.5558 which is equivalent to:\n   RA(J2000)  = +09h 02m 6.10s\n   Dec(J2000) = -40d 33' 20.9\"\nwith an uncertainty of 5.2 arcseconds (radius, 90% containment). This\nlocation is 83 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position is 9.5 arc seconds from Vela X-1. \nThis source is in the Swift XRT 1SXPS\ncatalogue with a mean 0.3-10 keV count-rate of 7.20 +/- 0.21 ct/sec;\nsee http://www.swift.ac.uk/1SXPS/1SXPSJ090206.7-403318 for details of\nthese previous observations. No event data are yet available to\ndetermine the column density using X-ray spectroscopy. \n\nThe initial flux in the 2.5 s image was 1.88e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 250 seconds with the U filter\nstarting  143 seconds after the BAT trigger. The optical counterpart\nto Vela X-1 is readily detected.",
  "circularId": 17068,
  "createdOn": 1416000950000,
  "email": "caryl@swift.psu.edu",
  "subject": "Trigger 618634: Swift detection of Vela X-1",
  "submitter": "Caryl Gronwall at PSU/Swift-UVOT  <caryl@swift.psu.edu>"
}