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GCN Circular 20807

Subject
LIGO/Virgo G275697: Further Swift-XRT sources
Date
2017-03-03T15:57:15Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
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), 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 1372 observations of galaxies (from the
2MPZ catalogue) within the LVC error region for the GW trigger G275697,
using the 'bayestar' GW localisation map. As this is a 3D skymap,
galaxy distances were taken into account in selecting which ones to
observe. The observations currently span from 15 ks to 256 ks after the
LVC trigger, and cover 165 sq degrees on the sky (corrected for
overlaps). This covers 0.16 of the probability in the LVC skymap, and
0.30 of the probability in the LVC map after convolving with the 2MPZ
galaxy catalogue, as described by Evans et al., (2016, MNRAS,  462,
1591).

Since the last Swift GCN, we have detected 6 X-ray sources, these are
either new detections, or have been given a higher 'rank' than in the
last circular. 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.

Source 14 was originally reported (in a COUNTERPART) notice as a rank 3
source, as no X-ray counterpart exists in the catalogues searched
automatically. However, an object does exist in the latest 3XMM-DR6
release, which corresponds to source 14, so it has been re-classified
as a rank 4, known source.

Source 8 was also originally reported as rank 3 (LVC Circ. 20798),
however it corresponds to a SIMBAD source 3C 33.1, which is a Seyfert
1, and has been detected by Chandra, therefore this has also been
re-classified as rank 4.

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 0 sources of rank 3
  * 6 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 9:
  =============
    RA: 	 331.2359 ( = 22h 04m 56.62s) J2000
    Dec:	 +47.2357 ( = +47d 14' 08.5") J2000
    Error:	 +5.5 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.5e-01 +/- 5.6e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 6.6e-12 +/- 2.4e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1SXPS J220456.4+471403 in the 1SXPS catalogue
    Separation:  5.4" from the XRT source
    Cat Rate:	 5.8e-01 +/- 2.7e-02 ct/sec 
    Cat Flux:	 2.5e-11 +/- 1.2e-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
      which is consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `V* HK Lac' is 4" away.
    There is 1 2MASS object within the source's 3-sigma error radius.
    NOTE: This source is affected by optical loading. The X-ray
detection appears real, but the flux may be inaccurate.
  
  Source 10:
  =============
    RA: 	 335.0282 ( = 22h 20m 6.77s) J2000
    Dec:	 +49.5037 ( = +49d 30' 13.3") J2000
    Error:	 +8.7 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.5e-01 +/- 5.9e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 6.6e-12 +/- 2.5e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1SXPS J222006.7+493011 in the 1SXPS catalogue
    Separation:  1.6" from the XRT source
    Cat Rate:	 1.5e-01 +/- 1.1e-02 ct/sec 
    Cat Flux:	 6.5e-12 +/- 4.7e-13 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
      which is consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `V* V383 Lac' is 3" away.
    There is 1 2MASS object within the source's 3-sigma error radius.
  
  Source 11:
  =============
    RA: 	 149.3249 ( = 09h 57m 17.98s) J2000
    Dec:	 -13.8334 ( = -13d 50' 00.2") J2000
    Error:	 +6.1 (arcsec, radius, 90% confidence).
    Peak Rate:	 2.5e-02 +/- 1.5e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 1.1e-12 +/- 6.4e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J095718.8-135031 in the ROSAT/RASSFSC catalogue
    Separation:  33.6" from the XRT source
    Cat Rate:	 1.7e-02 +/- 8.0e-03 ct/sec 
    Cat Flux:	 4.9e-13 +/- 2.2e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source  is 0.8-sigma above the catalogued flux.
    The source may be fading, at the 0.3-sigma level.
    There are 2 GWGC or 2MPZ galaxies within 200 kpc of the source.
      and consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `3FGL J0957.5-1351' is 3.3" away.
  
  Source 12:
  =============
    RA: 	 152.0125 ( = 10h 08m 3.00s) J2000
    Dec:	 -14.9836 ( = -14d 59' 01.0") J2000
    Error:	 +4.6 (arcsec, radius, 90% confidence).
    Peak Rate:	 6.9e-02 +/- 4.1e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 3.0e-12 +/- 1.8e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J100802.7-145904 in the ROSAT/RASSBSC catalogue
    Separation:  5.4" from the XRT source
    Cat Rate:	 2.9e-01 +/- 2.6e-02 ct/sec 
    Cat Flux:	 8.1e-12 +/- 7.4e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source is not above the catalogued flux.
    The source may be fading, at the 0.9-sigma level.
    There is 1 GWGC or 2MPZ galaxy within 200 kpc of the source.

      and consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `2MASX J10080288-1459066' is 6" away.
    There are 2 2MASS objects within the source's 3-sigma error radius.

  
  Source 13:
  =============
    RA: 	 150.9238 ( = 10h 03m 41.71s) J2000
    Dec:	 -15.1337 ( = -15d 08' 01.3") J2000
    Error:	 +5.6 (arcsec, radius, 90% confidence).
    Peak Rate:	 7.2e-02 +/- 5.5e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 3.1e-12 +/- 2.4e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J100343.2-150820 in the ROSAT/RASSFSC catalogue
    Separation:  28.8" from the XRT source
    Cat Rate:	 4.6e-02 +/- 1.3e-02 ct/sec 
    Cat Flux:	 1.3e-12 +/- 3.8e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source  is 0.8-sigma above the catalogued flux.
    The source may be fading, at the 1.1-sigma level.
    There are 2 GWGC or 2MPZ galaxies within 200 kpc of the source.
      and consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `[VV96] J100342.1-150808' is 8.2" away.
    There is 1 2MASS object within the source's 3-sigma error radius.
  
  Source 14:
  =============
    RA: 	 0.1318 ( = 00h 00m 31.63s) J2000
    Dec:	 +68.2501 ( = +68d 15' 00.4") J2000
    Error:	 +4.9 (arcsec, radius, 90% confidence).
    Peak Rate:	 2.8e-02 +/- 8.8e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 1.2e-12 +/- 3.8e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:   in the  catalogue
    Separation:  2.0" from the XRT source
    Cat Rate:	 3.7e-01 +/- 7.8e-03 ct/sec 
    Cat Flux:	 9.9e-13 +/- 2.1e-14 erg cm^-2 s^-1 (0.3-10 keV)
       so the source  is 0.6-sigma above the catalogued flux.
    There is no evidence for fading.
    There are 2 GWGC or 2MPZ galaxies within 200 kpc of the source.
      and consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `BD+67  1587' is 2" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

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