{
  "bibcode": "2019GCN.23925....1K",
  "body": "A. Keivani (Columbia U.), P. A. Evans (U. Leicester), D. B. Fox (PSU), J.\nA. Kennea (PSU),  D. F. Cowen (PSU), J. P. Osborne (U. Leicester), F. E.\nMarshall (GSFC), Marcos Santander (U. Alabama), Miguel Mostafa (PSU), and\nHugo Ayala (PSU) report:\n\n\nThe Neil Gehrels Swift Observatory observed the field of the IceCube HESE\nastrophysical neutrino candidate IceCube-190221A (revision 1,\nhttps://gcn.gsfc.nasa.gov/gcn3/23918.gcn3) beginning Feb 21.6 UT (6.55h\nafter the neutrino detection), utilizing its onboard 19-point tiling\npattern to cover a region centered on R.A., Dec. (J2000) = 268.81d,\n-17.04d, with a radius of approximately 0.8 degrees; estimated\n90%-containment radii for this event are 0.5 deg to 1.8 deg depending on\nposition angle. Earlier observations targeting the pre-revision\nlocalization R.A., Dec. (J2000) = 267.3650d, -16.9379d beginning ~2 hours\nafter the neutrino arrival time have also been executed, and are not\nreported here.\n\nSwift-XRT collected ~400 s per field of PC mode data per tile between 14:58:40\nUT and 21:34:12 UT on 21 February (6.55h to 13.14h after the neutrino\ndetection) over 2.1 square degrees. Data have been reduced using the\nanalysis approach and software routines of Evans et al. 2014 (ApJS, 210,\n8).\n\nThree X-ray sources are detected in these data, two of which likely\ncorrespond to the stars HD 162561 (2MASS J17521921-1658102) and TYC\n6254-1118-1 (2MASS J17531121-1725423). The third X-ray source is located at\nR.A. 17h 53m 50.24s, Dec. -16d 18��� 45.1��� (J2000) with an uncertainty of\n4.8��� (90%-confidence radius) and matches the known X-ray source XMMSL2\nJ175349.9-161846 from the XMM-Newton slew survey (3.7��� distance). The\nsource���s mean observed XRT count rate is 3.9 (+1.5, -1.2) e-2 ct s^-1,\nwhich is 1.7-sigma below the XMMSL2 catalog flux.\n\nThe 3-sigma upper limit on the count rate of any point-like counterpart\nover the rest of the tiled region is 0.02 ct s^-1, which corresponds to a\n0.3-10 keV flux of 8.0e-13 erg cm^-2 s^-1 for a typical AGN spectrum\n(nH=3e20 cm^-2, Gamma=1.7).",
  "circularId": 23925,
  "createdOn": 1550867620000,
  "email": "azadeh.keivani@columbia.edu",
  "subject": "IceCube-190221A: Swift-XRT Follow-up Observations",
  "submitter": "Azadeh Keivani at Columbia U  <azadeh.keivani@columbia.edu>",
  "eventId": "IceCube-190221A"
}