{
  "bibcode": "2017GCN.20415....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), N. Gehrels (NASA/GSFC), P. Giommi (ASI), C. Gronwall\n(PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien\n(GSFC/UMBC), D. Malesani (DARK/NBI), F.E. Marshall (NASA/GSFC), A.\nMelandri (INAF-OAB), B. Mingo (U. Leicester),  J.A. Nousek (PSU), S.R.\nOates (U. Warwick), P.T. O'Brien (U. Leicester), J.P. Osborne (U.\nLeicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M.\nPalmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti\n(INAF-OAB/PSU), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja\n(NASA/GSFC/UMCP) report on behalf of the Swift team:\n\nSwift has continued to observed ATLAS17aeu (Tonry et al., LVC Circ.\n20382), gathering a total of 21.3 ks of data, from T0+222 ks to T0+470\nks (where T0 is the GW trigger time). The X-ray counterpart (Evans et\nal., LVC Circ. 20390) is now confirmed to be fading.\n\nAssuming the trigger time from the GW event (LVC Circ. 20364) the light\ncurve is decaying with a power-law index of 2.2 (+1.1, -1.2). If instead\nwe take T0 from GRB 170105A (Marcinkowski et al., GCN Circ. 20387), the\ndecay index is 1.7 (+1.1, -0.9). At the mid-point of the latest \nobservation, GW_T0+453 ks (=GRB_T0+381 ks) the 0.3-10 keV XRT count-rate\nwas 0.0017 (+/- 0.0006) ct/sec.\n\nA spectrum compiled from the data can be fitted with an absorbed\npower-law, with NH consistent with the Galactic value of 4.6e20 cm^-2\n(Willingale et al. 2013) and photon index Gamma=1.60 (+0.4, -0.3).\n\nUsing this spectrum the count-rate above corresponds to an observed\n(unabsorbed) 0.3-10 keV flux of (6.7+/-2.4)e-14  ( [7.2+/-2.6]e-14) erg\ncm^-2 s^-1.\n\nThe spectral and temporal indices are consistent with the values\ntypically seen for X-ray GRB afterglows (e.g. the Swift-XRT GRB\ncatalogue: http://www.swift.ac.uk/xrt_live_cat/; Evans et al. 2009).\n\nThis circular is an official product of the Swift GW follow up team.",
  "circularId": 20415,
  "createdOn": 1484041526000,
  "email": "pae9@leicester.ac.uk",
  "subject": "LIGO/Virgo G268556: Swift-XRT confirms that ATLAS17aeu is fading in X-rays",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "LIGO/Virgo G268556"
}