{
  "submittedHow": "email",
  "subject": "LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources",
  "createdOn": 1763133333584,
  "eventId": "LIGO/Virgo/KAGRA S251112cm",
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "bibcode": "2025GCN.42681....1P",
  "body": "K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.\nTohuvavohu (Cosmic Frontier Labs), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U.\nLeicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld\n(UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De Pasquale (University\nof Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) ,\nV. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson\nUniversity), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S.\nLaha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P.\nO’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T.\nSbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri\n(INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team:\n\nSwift has carried out 105 observations of the LVK error region for the GW trigger\nS251112cm convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9),\nusing the 'BAYESTAR' (version BAYESTAR.fits.gz) GW localisation map. As this is a 3D\nskymap, galaxy distances were taken into account in selecting which ones to observe.\nThe observations currently span from 7.6 ks to 117 ks after the LVK trigger, and the\nXRT has covered 12.7 deg^2 on the sky (corrected for overlaps). This covers 1.3% of\nthe probability in the 'BAYESTAR' (version BAYESTAR.fits.gz) skymap, and 20% after\nconvolving with the 2MPZ galaxy catalogue, as described by Evans et al. (2016,\nMNRAS,\t462, 1591).\n\nWe have detected 20 X-ray sources. Each source is assigned a rank of 1-4 which\ndescribes how likely it is to be related to the GW trigger, with 1 being the most\nlikely and 4 being the least likely. The ranks are described at\nhttps://www.swift.ac.uk/ranks.php.\n\nWe have found:\n\n  * 0 sources of rank 1\n  * 0 sources of rank 2\n  * 7 sources of rank 3\n  * 13 sources of rank 4\n\n\nRANK 3 sources\n==============\n\nThese are uncatalogued X-ray sources, however they are not brighter than previous\nupper limits, so do not stand out as likely counterparts to the GW trigger.\n\n| Source ID\t | RA\t\t  | Dec \t   | Err90   | Detection Flag\t|\n|  S251112cm_X1  |    11 09 55.90 |    +36 08 20.7 |\t8.0\" |\t\t   POOR |\n| S251112cm_X38  |    23 47 03.18 |    -28 07 08.2 |\t9.5\" |\t\t   POOR |\n| S251112cm_X53  |    11 08 18.65 |    +36 11 04.6 |\t8.1\" |\t\t   POOR |\n| S251112cm_X72  |    12 22 09.27 |    +55 52 20.4 |\t5.9\" |\t\t   GOOD |\n| S251112cm_X73  |    01 08 29.26 |    -46 59 48.1 |\t8.9\" |\t\t   POOR |\n| S251112cm_X78  |    23 48 35.23 |    -28 14 05.5 |\t9.8\" |\t\t   POOR |\n| S251112cm_X79  |    23 48 06.04 |    -28 04 35.1 |   12.3\" |\t\t   POOR |\n\n\nRANK 4 sources\n==============\n\nThese are catalogued X-ray sources, showing no signs of outburst compared to\nprevious observations, so they are not likely to be related to the GW trigger.\n\n| Source ID\t | RA\t\t  | Dec \t   | Err90   | Detection Flag\t|\n|  S251112cm_X2  |    11 12 06.93 |    +35 27 45.6 |\t6.8\" |\t\t   GOOD |\n|  S251112cm_X3  |    09 20 46.26 |    -08 03 21.4 |\t5.5\" |\t\t   GOOD |\n|  S251112cm_X5  |    23 51 37.99 |    -28 18 18.1 |\t7.6\" |\t\t   POOR |\n| S251112cm_X50  |    11 37 24.49 |    +47 27 44.7 |\t7.4\" |\t\t   GOOD |\n| S251112cm_X51  |    01 08 20.79 |    -47 07 36.3 |\t7.4\" |\t\t   POOR |\n| S251112cm_X52  |    01 07 42.60 |    -46 54 24.5 |\t6.1\" |\t\t   GOOD |\n| S251112cm_X67  |    11 11 04.66 |    +35 13 59.3 |\t6.9\" |\t\t   GOOD |\n| S251112cm_X68  |    22 44 47.97 |    -00 06 17.5 |\t8.8\" |\t\t   GOOD |\n| S251112cm_X69  |    02 36 19.70 |    -54 51 50.8 |\t5.8\" |\t\t   GOOD |\n| S251112cm_X70  |    13 06 57.05 |    +59 58 48.1 |   10.7\" |\t     REASONABLE |\n| S251112cm_X71  |    12 23 00.00 |    +55 40 04.4 |\t5.1\" |\t\t   GOOD |\n| S251112cm_X87  |    11 12 01.25 |    +37 58 26.3 |\t6.1\" |\t\t   GOOD |\n| S251112cm_X88  |    11 04 27.52 |    +38 12 36.6 |\t3.5\" |\t\t   GOOD |\n\nFor all flux conversions and comparisons with catalogues and upper limits from other\nmissions, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index\n(Gamma)=1.7, unless otherwise stated.\n\nThe results of the XRT automated analysis, including details of the sources listed\nabove, are online at https://www.swift.ac.uk/LVC/S251112cm\n\nThis circular is an official product of the Swift XRT team.\n\n\n",
  "circularId": 42681
}