{
  "bibcode": "2017GCN.20773....1E",
  "body": "P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.D. Barthelmy\n(NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL),\nD.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), G.\nCusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB),\nV.D'Elia(ASDC), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm\n(CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), D.\nMalesani (DARK/NBI), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),\nB. Mingo (U. Leicester),  J.A. Nousek (PSU), S.R. Oates (U. Warwick),\nP.T. O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C. Pagani (U.\nLeicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri\n(ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H.\nSiegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP)\nreport on behalf of the Swift team:\n\nSwift has performed a series of 62 observations of galaxies (from the\n2MPZ catalogue) within the LVC error region for the GW trigger G275697,\nusing the 'bayestar' GW localisation map. As this is a 3D skymap,\ngalaxy distances were taken into account in selecting which ones to\nobserve. The observations currently span from 15 ks to 24 ks after the\nLVC trigger, and cover 7.6 sq degrees on the sky (corrected for\noverlaps). This covers 0.011 of the probability in the LVC skymap, and\n0.022 of the probability in the LVC map after convolving with the 2MPZ\ngalaxy catalogue, as described by Evans et al., (2016, MNRAS,  462,\n1591).\n\nWe have detected a 1 X-ray source. Each source is assigned a rank of\n1-4 which describes how likely it is to be related to the GW trigger,\nwith 1 being the most likely and 4 being the least likely. The ranks\nare described at http://www.swift.ac.uk/ranks.php.\n\nThe detected source is currently given \"rank 3\" since it is only\n1.6-sigma above the historical upper limit at this location from the\nRosat All Sky Survey, and therefore cannot be identified as a new\nsource with a significant degree of confidence. We only have a single\ndata point so cannot comment on variability. We note, however, that\nthis uncatalogued source is consistent with a galaxy in 2MPZ with a\ndistance (based on a photometric redshift) of at 291 �� 61 Mpc. The\nLIGO distance probability on the line of sight to this has mean 160 and\nsigma 57 Mpc. 96% of the integral of the LIGO distance function (Singer\net al., 2016, ApJL, 829, 15) along this line of sight lies within the\n3-sigma confidence interval on this galaxy's position. Follow up\nobservations of this source are encouraged. \n\nWe have found:\n\n  * 0 sources of rank 1\n  * 0 sources of rank 2\n  * 1 source of rank 3\n  * 0 sources of rank 4\n\nFor all flux conversions and comparisons with catalogues and upper\nlimits from other missions, we assumed a power-law spectrum with\nNH=3e20 cm^2, and photon index (Gamma)=1.7\n\n\nRANK 3 sources\n==============\n\nThese are uncatalogued X-ray sources, however they are not brighter\nthan previous upper limits, so do not stand out as likely counterparts\nto the GW trigger.\n  \n  Source 1:\n  =============\n    RA: \t 324.9781 ( = 21h 39m 54.74s) J2000\n    Dec:\t +44.7641 ( = +44d 45' 50.8\") J2000\n    Error:\t +5.9 (arcsec, radius, 90% confidence).\n    Peak Rate:\t 1.1e-01 +/- 5.0e-02 ct/sec (0.3-10 keV)\n    Peak Flux:\t 4.7e-12 +/- 2.1e-12 erg cm^-2 s^-1 (0.3-10 keV)\n    1XMM UL:\t 7.4e-12 ct/sec, (0.3-10 keV)\n\t\t So the source is 1.3-sigma above the \n\t\t XMM 3-sigma upper limit.\n    RASS UL:\t 3.0e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)\n\n\t\t So the source is not above the RASS 3-sigma upper \n\t\t limit.\n    There is no evidence for fading.\n    There is 1 GWGC or 2MPZ galaxy within 200 kpc of the source,\n    and consistent (within 3-sigma) with the distance to the GW object.\n\n    There is 1 2MASS object within the source's 3-sigma error radius.\n\nThis circular is an official product of the Swift team.",
  "circularId": 20773,
  "createdOn": 1488272392000,
  "email": "pae9@leicester.ac.uk",
  "subject": "LIGO/Virgo G275697: Swift-XRT sources",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "LIGO/Virgo G275697"
}