{
  "bibcode": "2020GCN.26798....1E",
  "body": "P.A. Evans (U. Leicester),  K.L. Page (U.Leicester), J.A. Kennea (PSU),\nA. Tohuvavohu (U. Toronto), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore\n(U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL),\nP. Brown (TAMU), D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko\n(NASA/GSFC), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P.\nD'Avanzo (INAF-OAB), V. D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P.\nGiommi (ASI), C. Gronwall (PSU), D. Hartmann (U. Clemson), H.A. Krimm\n(CRESST/GSFC/USRA), N.J. Klingler (PSU), N.P.M. Kuin (UCL-MSSL), A.Y.\nLien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),\nJ.A. Nousek (PSU), S.R. Oates (U. Birmingham), P.T. O'Brien (U.\nLeicester), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester),\nM.J.Page (UCL-MSSL), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin\n(NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G.\nTagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP) report on behalf of\nthe Swift team:\n\nSwift has carried out 456 observations of the LVC error region for the\nGW trigger S200115j convolved with the 2MPZ catalogue (Bilicki et al.\n2014, ApJS, 210, 9), using 23 fields from the 'bayestar' (version 0) GW\nlocalisation map and 433 fields from the 'bayestar' (version 2) GW\nlocalisation map. As these are 3D skymaps, galaxy distances were taken\ninto account in selecting which ones to observe. The observations\ncurrently span from 7.1 ks to 164 ks after the LVC trigger, and the XRT\nhas covered 28.5 deg^2 on the sky (corrected for overlaps). This covers\n12% of the probability in the 'bayestar' (version 2) skymap, and 24%\nafter convolving with the 2MPZ galaxy catalogue, as described by Evans\net al. (2016, MNRAS,  462, 1591). Using the earlier  'bayestar'\n(version 0) skymap our observations cover 7.8% of the probability (16%\nwhen convolved). These pointings and associated metadata have been\nreported to the Treasure Map (Wyatt et al., arXiv 2001.00588;\nhttp://treasuremap.space/alerts?graceids=S200115j).\n\n2 rank 2 sources have been found. These are candidates to be the\ncounterpart to the GW trigger. Details of these sources are:\n  \n  Source S200115j_X130:\n  =============\n    RA: \t 44.9028 ( = 02h 59m 36.67s) J2000\n    Dec:\t +7.4042 ( = +07d 24' 15.1\") J2000\n    Error:\t 4.7 (arcsec, radius, 90% confidence).\n    Peak Rate:\t 2.7e-02 +/- 6.9e-03 ct/sec (0.3-10 keV)\n    Peak Flux:\t 1.2e-12 +/- 3.0e-13 erg cm^-2 s^-1 (0.3-10 keV)\n    Catalogued:  Yes\n    Cat Source:  1WGA J0259.6+0724 in the ROSAT/WGACAT catalogue\n    Separation:  6.5\" from the XRT source\n    Cat Rate:\t 4.9e-03 +/- 1.8e-03 ct/sec \n    Cat Flux:\t 1.5e-13 +/- 5.5e-14 erg cm^-2 s^-1 (0.3-10 keV)\n\t\t So the source\tis 3.4-sigma above the catalogued flux.\n\n    There is 1 GWGC or 2MPZ galaxy within 200 kpc of the source.\n    \nThe determination that this source has brightened compared to the ROSAT\ndata is of course dependent on the assumed X-ray spectrum: if the\nsource is heavily absorbed then the brightness increase becomes less\nnoteworthy. Unfortunately, we have insufficient data to investigate the\nspectrum at the present time. Further observations are expected.\n    \n  \n  Source S200115j_X136:\n  =============\n    RA: \t 40.0508 ( = 02h 40m 12.19s) J2000\n    Dec:\t -2.5626 ( = -02d 33' 45.4\") J2000\n    Error:\t 4.7 (arcsec, radius, 90% confidence).\n    Peak Rate:\t 8.6e-02 +/- 1.7e-02 ct/sec (0.3-10 keV)\n    Peak Flux:\t 3.7e-12 +/- 7.2e-13 erg cm^-2 s^-1 (0.3-10 keV)\n    Catalogued:  Yes\n    Cat Source:  2SXPS J024012.0-023340 in the 2SXPS catalogue\n    Separation:  4.9\" from the XRT source\n    Cat Rate:\t 6.7e-03 +/- 1.6e-03 ct/sec \n    Cat Flux:\t 2.9e-13 +/- 6.9e-14 erg cm^-2 s^-1 (0.3-10 keV)\n       so the source  is 4.7-sigma above the catalogued flux.\n\nThis source has been observed multiple times by Swift-XRT before, and\nits historical light curve can be seen at\nhttps://www.swift.ac.uk/2SXPS/2SXPS%20J024012.0-023340. This source is\ncoincident with a 2MASS galaxy, and given the historical data, we\nassume that this galaxy is an AGN. Therefore the flux increase compared\nto previous Swift observations may simply reflect AGN activity, or may\nindicate a transient within that galaxy (as was the case for GW 170817,\nwhose host galaxy was an X-ray emitter). Further observations are\nexpected.\n\n\nIn total, we have detected 14 X-ray sources. Each source is assigned a\nrank of 1-4 which describes how likely it is to be related to the GW\ntrigger, with 1 being the most likely and 4 being the least likely. The\nranks are described at https://www.swift.ac.uk/ranks.php.\n\nWe have found:\n\n  * 0 sources of rank 1\n  * 2 sources of rank 2\n  * 3 sources of rank 3\n  * 9 sources of rank 4\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 ID\t | RA\t\t  | Dec \t   | Err90   |\n|  S200115j_X62  | 02h 48m 23.89s | +05d 34' 46.4\" |\t4.5\" |\n|  S200115j_X63  | 02h 47m 25.18s | +05d 29' 41.7\" |\t7.0\" |\n| S200115j_X135  | 02h 42m 11.50s | -03d 08' 13.8\" |   28.4\" |\n\n\nRANK 4 sources\n==============\n\nThese are catalogued X-ray sources, showing no signs of outburst\ncompared to previous observations, so they are not likely to be related\nto the GW trigger.\n\n| Source ID\t | RA\t\t  | Dec \t   | Err90   |\n|  S200115j_X40  | 02h 46m 14.64s | +05d 35' 29.9\" |\t4.5\" |\n|  S200115j_X73  |  02h 27m 0.61s | -04d 20' 20.3\" |\t6.9\" |\n|  S200115j_X74  | 02h 47m 27.22s | -00d 12' 21.5\" |\t3.9\" |\n|  S200115j_X75  | 02h 55m 14.42s | +09d 06' 26.6\" |\t8.3\" |\n|  S200115j_X76  | 02h 38m 27.56s | +01d 54' 29.5\" |\t4.8\" |\n| S200115j_X105  | 03h 57m 45.52s | +41d 55' 07.9\" |\t5.0\" |\n| S200115j_X106  | 03h 56m 57.58s | +42d 55' 44.3\" |\t4.4\" |\n| S200115j_X127  | 02h 58m 51.32s | +06d 22' 26.4\" |\t5.2\" |\n| S200115j_X134  | 02h 42m 40.74s | +00d 57' 31.5\" |\t4.8\" |\n\nFor all flux conversions and comparisons with catalogues and upper\nlimits from other missions, we assumed a power-law spectrum with\nNH=3x10^20 cm^-2, and photon index (Gamma)=1.7\n\nThe results of the XRT automated analysis, including details of the\nsources listed above, are online at\nhttps://www.swift.ac.uk/LVC/S200115j\n\nThis circular is an official product of the Swift XRT team.",
  "circularId": 26798,
  "createdOn": 1579258700000,
  "email": "pae9@leicester.ac.uk",
  "subject": "LIGO/Virgo S200115j: Swift-XRT sources",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "LIGO/Virgo S200115j"
}