GCN Circular 20371

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.