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GCN Circular 18834

LIGO/Virgo G211117: Further Swift-XRT sources
2016-01-06T09:33:46Z (8 years ago)
Phil Evans at U of Leicester <>
P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.D. Barthelmy
(NASA/GSFC), D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko
(NASA/GSFC), N. Gehrels (NASA/GSFC), P. Giommi (ASI), F.E. Marshall
(NASA/GSFC), J.A. Nousek (PSU), P.T. O'Brien (U. Leicester), J.P.
Osborne (U. Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L.
Racusin (NASA/GSFC), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB)
report on behalf of the Swift team:

Swift has performed a series of 76 observations of galaxies (from the
GWGC catalogue) within the aLIGO error region for the aLIGO trigger
G211117, using the 'bayestar' GW localisation map. The observations
currently span from 140 ks to 914 ks after the aLIGO trigger, and cover
8.6 sq degrees on the sky (corrected for overlaps).

Since the last Swift GCN, we have detected 2 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

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 1 source of rank 3
  * 1 source of rank 4

In addition, we observed the location of the source PS15dqa (from
Smartt et al., GCN Circ. 18824), an optical transient in NGC 1156 at a
distance of just 7 Mpc. No X-ray emission was detected at the location
of PS15dqa to a 3-sigma upper limit of 4.1e-3 ct/sec, corresponding to
a flux of 1.8e-13 erg/cm^2/s.

We assumed a power-law spectrum with NH=3e20 cm^2, and photon index

RANK 3 sources

These are uncatalogued X-ray sources, however they are not brighter
than previous upper limits, so do not stand out as likely counterparts
to the GW trigger.
  Source 53:
    RA: 	 44.9257 ( = 02h 59m 42.17s) J2000
    Dec:	 +25.2129 ( = +25d 12' 46.4") J2000
    Error:	 +5.8 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.5e-03 +/- 7.9e-04 ct/sec (0.3-10 keV)
    Peak Flux:	 6.3e-14 +/- 3.4e-14 erg cm^-2 s^-1 (0.3-10 keV)
    RASS UL:	 3.0e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

       so the source is not above the RASS 3-sigma upper limit.
    There is no evidence for fading.
    There is 1 GWGC galaxy within 200 kpc of the source.

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 54:
    RA: 	 202.5319 ( = 13h 30m 7.66s) J2000
    Dec:	 -20.9364 ( = -20d 56' 11.0") J2000
    Error:	 +6.0 (arcsec, radius, 90% confidence).
    Peak Rate:	 2.0e-02 +/- 7.3e-03 ct/sec (0.3-10 keV)
    Peak Flux:	 8.5e-13 +/- 3.1e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1SXPS J133007.7-205619 in the 1SXPS catalogue
    Separation:  8.4" from the XRT source
    Cat Rate:	 1.6e-02 +/- 1.6e-03 ct/sec (0.3-10 keV)
    Cat Flux:	 6.8e-13 +/- 6.9e-14 erg cm^-2 s^-1 (0.3-10 keV)
       so the source  is 0.5-sigma above the catalogued flux.
    There is no evidence for fading.
    There is 1 GWGC galaxy within 200 kpc of the source.
    A SIMBAD object `[RKV2003] QSO J1330-2056 abs 0.84992' is 5.3"
    There is 1 2MASS object within the source's 3-sigma error radius.

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