{
  "bibcode": "2014GCN.16332....1B",
  "body": "S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),\nS. B. Cenko (GSFC), V. D'Elia (ASDC), D. Malesani (DARK/NBI),\nV. Mangano (PSU), F. E. Marshall (NASA/GSFC) and\nB. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:\n\nAt 21:24:27 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated a source in M31 (NGC224) (trigger=600114).  Swift slewed immediately\nto the target.  The BAT on-board calculated location is \nRA, Dec 10.402, +41.556, which is \n   RA(J2000)  =  00h 41m 37s\n   Dec(J2000) = +41d 33' 23\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  This is an image trigger of 64 second duration,\nwith significance 6.18 sigma, which is lower than typical blind detection \nsignificance.  The BAT light curve does not show obvious structure, which \nis typical for image triggers. \n\nThe XRT began observing the field at 21:27:05.4 UT, 157.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find an X-ray source\nwith an enhanced position: RA, Dec 10.4292, 41.5734 which is equivalent to:\n   RA(J2000)  = 00h 41m 43.02s\n   Dec(J2000) = +41d 34' 24.3\"\nwith an uncertainty of 2.9 arcseconds (radius, 90% containment). This\nlocation is 96 arcseconds from the BAT onboard position, within the BAT\nerror circle. The XRT position may be improved as\nmore data are received; the latest position is available at\nhttp://www.swift.ac.uk/sper. This position is 4.0 arcseconds from that\nof a known X-ray source: 3XMM J004143.0+413420 in the XMM-NEWTON XMMSSC\ncatalogue. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 1.81\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nThe associated source in the 3rd XMM catalog has a spectrum and variability\nwhich is consistent with a low-mass X-ray binary (Stiele 2010).  However,\nthe target is also spatially consistent with a globular cluster FMZ2005-7 of M31. \nThere may be multiple X-ray binaries within the same globular cluster. \n\nThe XRT count rate is approximately 30 counts per second.  Assuming a typical\nconversion factor to flux, the 0.3-10 keV flux is approximately 1e-9 erg/cm2/s\n(uncertain to a factor of 2x).  At the distance of Andromeda, this would be a\nluminosity of 7e40 erg/s (uncertain to the same factor). \n\nThis luminosity is clearly super-Eddington for a ~solar mass compact object,\nso either the object is of ULX class, or it is significantly beamed. \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 162 seconds after the BAT trigger. UVOT detects a 16.9 mag source\nat the position\n  RA (J2000) = 00:41:43.10 = 10.42957\n  Dec(J2000) =+41:34:20.4  = 41.57232\nwith a 90% confidence error radius of 0.61 arc sec. \nThis position is 4 arc seconds from the center of the XRT error circle\nand consistent with the position of the globular cluster. \nNo correction has been made for the expected extinction corresponding to E(B-V) of 0.06.",
  "circularId": 16332,
  "createdOn": 1401228908000,
  "email": "scott@milkyway.gsfc.nasa.gov",
  "subject": "Swift detection of a bright X-ray source in M31",
  "submitter": "Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>"
}