TITLE: GCN CIRCULAR NUMBER: 20371 SUBJECT: LIGO/Virgo G268556: Swift-XRT sources DATE: 17/01/05 17:45:23 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL), D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), N. Gehrels (NASA/GSFC), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), D. Malesani (DARK/NBI), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), B. Mingo (U. Leicester), J.A. Nousek (PSU), S.R. Oates (U. Warwick), P.T. O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team: Swift has performed a series of 291 observations of galaxies (from the GWGC catalogue) within the LVC error region for the GW trigger G268556, using the 'bayestar' GW localisation map. The observations currently span from 50 ks to 86 ks after the LVC trigger, and cover 31.3 sq degrees on the sky (corrected for overlaps). This covers 0.047 of the probability in the LVC skymap, and 0.051 of the probability in the LVC map after weighting by galaxies in the GWGC catalogue. We have detected 3 X-ray sources. Each source is assigned a rank of 1-4 which describes how likely it is to be related to the GW trigger, with 1 being the most likely and 4 being the least likely. The ranks are described at http://www.swift.ac.uk/ranks.php. We have found: * 0 sources of rank 1 * 0 sources of rank 2 * 0 sources of rank 3 * 3 sources of rank 4 For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3e20 cm^2, and photon index (Gamma)=1.7 RANK 4 sources ============== These are catalogued X-ray sources, showing no signs of outburst compared to previous observations, so they are not likely to be related to the GW trigger. Source 1: ============= RA: 133.0839 ( = 08h 52m 20.14s) J2000 Dec: +47.5827 ( = +47d 34' 57.7") J2000 Error: +5.4 (arcsec, radius, 90% confidence). Peak Rate: 1.8e-01 +/- 6.7e-02 ct/sec (0.3-10 keV) Peak Flux: 7.9e-12 +/- 2.9e-12 erg cm^-2 s^-1 (0.3-10 keV) Cat Source: 1RXS J085218.0+473456 in the ROSAT/RASSBSC catalogue Separation: 21.8" from the XRT source Cat Rate: 6.9e-02 +/- 1.4e-02 ct/sec Cat Flux: 1.9e-12 +/- 3.8e-13 erg cm^-2 s^-1 (0.3-10 keV) so the source is 2.1-sigma above the catalogued flux. There is no evidence for fading. NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy. A SIMBAD object `[VV2006] J085220.5+473458' is 3.1" away. Source 2: ============= RA: 133.4418 ( = 08h 53m 46.03s) J2000 Dec: +47.3117 ( = +47d 18' 42.1") J2000 Error: +5.0 (arcsec, radius, 90% confidence). Peak Rate: 2.1e-01 +/- 6.8e-02 ct/sec (0.3-10 keV) Peak Flux: 9.1e-12 +/- 2.9e-12 erg cm^-2 s^-1 (0.3-10 keV) Cat Source: 1RXS J085345.1+471847 in the ROSAT/RASSBSC catalogue Separation: 10.6" from the XRT source Cat Rate: 1.8e-01 +/- 2.3e-02 ct/sec Cat Flux: 5.2e-12 +/- 6.5e-13 erg cm^-2 s^-1 (0.3-10 keV) so the source is 1.3-sigma above the catalogued flux. There is no evidence for fading. NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy. A SIMBAD object `BD+47 1620' is 2.8" away. There is 1 2MASS object within the source's 3-sigma error radius. Source 3: ============= RA: 350.3156 ( = 23h 21m 15.74s) J2000 Dec: -26.9822 ( = -26d 58' 55.9") J2000 Error: +7.6 (arcsec, radius, 90% confidence). Peak Rate: 2.6e-01 +/- 6.0e-02 ct/sec (0.3-10 keV) Peak Flux: 1.1e-11 +/- 2.6e-12 erg cm^-2 s^-1 (0.3-10 keV) Cat Source: 2RXP J232115.1-265908 in the ROSAT/ROSPSPC catalogue Separation: 15.4" from the XRT source Cat Rate: 1.9e+00 +/- 7.6e-02 ct/sec Cat Flux: 5.2e-11 +/- 2.1e-12 erg cm^-2 s^-1 (0.3-10 keV) so the source is not above the catalogued flux. There is no evidence for fading. NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy. NOTE: The source is close to a ~6 mag star (HR 8883) thus the X-ray flux may be distorted by the presence of optical photons. This circular is an official product of the Swift team.