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GCN Circular 26787

LIGO/Virgo S200114f: Swift-XRT sources and observations
2020-01-16T14:39:16Z (4 years ago)
Phil Evans at U of Leicester <>
P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester),
M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), P. Brown (TAMU),
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), S.W.K. Emery (UCL-MSSL), P. Giommi (ASI), C. Gronwall
(PSU), D. Hartmann (U. Clemson), H.A. Krimm (CRESST/GSFC/USRA), N.J.
Klingler (PSU), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E.
Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R.
Oates (U. Birmingham), P.T. O'Brien (U. Leicester), J.P. Osborne (U.
Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), M.J.Page
(UCL-MSSL), 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 carried out 206 observations of the LVC error region for the
GW trigger S200114f following the 'cWB' (version 3) GW localisation
map. The observations currently span from 6.6 ks to 99 ks after the LVC
trigger, and the XRT has covered 22.3 deg^2 on the sky (corrected for
overlaps). This covers 30% of the probability in the 'cWB' (version 3)
skymap. These pointings and associated metadata have been reported to
the Treasure Map (Wyatt et al., arXiv 2001.00588;

A 'rank 2' source has been found, so classified because it shows
indications of fading, however it is spatially consistent with a source
in the WISE AGN candidates catalogs (Assef et al., 2018) and therefore
may simply be a variable AGN. The details of this source are:
  Source 2:
    RA: 	 110.3641 ( = 07h 21m 27.38s) J2000
    Dec:	 +17.0360 ( = +17d 02' 09.6") J2000
    Error:	 7.0 (arcsec, radius, 90% confidence).
    Peak Rate:	 9.6e-02 +/- 1.7e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 4.1e-12 +/- 7.5e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Catalogued:  No
    RASS UL:	 3.5e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)

Further observations of this source are scheduled.

In total, we have detected 8 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

We have found:

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

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 ID	 | RA		  | Dec 	   | Err90   |
|  S200114f_X1	 | 07h 13m 48.09s | +23d 04' 50.5" |	7.5" |
|  S200114f_X10  | 03h 41m 58.28s | -25d 24' 17.6" |	6.1" |
|  S200114f_X46  | 03h 41m 1.50s  | -25d 26' 54.4" |	6.4" |
|  S200114f_X56  | 07h 22m 51.63s | +16d 15' 51.0" |	6.3" |
|  S200114f_X57  | 07h 23m 54.09s | +16d 22' 00.1" |	7.7" |
|  S200114f_X58  | 07h 23m 50.42s | +16d 21' 17.1" |	6.7" |

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 ID	 | RA		  | Dec 	   | Err90   |
|  S200114f_X59  |  07h 15m 9.23s | +15d 55' 36.9" |	8.3" |

The Swift-XRT observations also covered the locations of 6 sources
reported by other observers, thus:

* AT2020vr (GCN26741)		F < 3.3x10^-12 erg cm^-2 s^-1.
* AT2020vs (GCN26741)		F < 2.0x10^-12 erg cm^-2 s^-1.
* AT2020vt (GCN26741)		F < 4.2x10^-12 erg cm^-2 s^-1.
* AT2020vu (GCN26741)		F < 8.6x10^-12 erg cm^-2 s^-1.
* AT2020vw (GCN26741)		F < 4.7x10^-12 erg cm^-2 s^-1.
* AT2020wc (GCN26741)		F < 1.7x10^-11 erg cm^-2 s^-1.

Flux limits are 3-sigma upper limits on the 0.3-10 keV observed flux.

For all flux conversions and comparisons with catalogues and upper
limits from other missions, we assumed a power-law spectrum with
NH=3x10^20 cm^-2, and photon index (Gamma)=1.7

The results of the XRT automated analysis, including details of the
sources listed above, are online at

This circular is an official product of the Swift XRT team.
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