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GCN Circular 25400

LIGO/Virgo S190814bv: No strong counterpart candidates in Swift/XRT observations
2019-08-19T13:58:13Z (5 years ago)
Phil Evans at U of Leicester <>
P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (PSU), 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
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.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. Warwick), 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 451 observations of the LVC error region for the
GW trigger S190814bv convolved with the 2MPZ catalogue (Bilicki et al.
2014, ApJS, 210, 9), using 128 fields from the 'bayestar' GW
localisation map and 323 fields from the 'LALInference.v1' GW
localisation map. As these are 3D skymaps, galaxy distances were taken
into account in selecting which ones to observe. The observations
currently span from 11 ks to 385 ks after the LVC trigger, and the XRT
has covered 20.1 deg^2 on the sky (corrected for overlaps). This
covers 81% of the probability in the 'LALInference.v1' skymap, and 89%
after convolving with the 2MPZ galaxy catalogue, as described by Evans
et al. (2016, MNRAS,  462, 1591). Using the earlier  'bayestar' skymap
our observations cover 70% of the probability (78% when convolved).
Approximately 40% of the fields, covering 60% of the (galaxy convolved) 
GW probability, have been observed more than once.

We have detected 40 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
   * 0 sources of rank 2
   * 17 sources of rank 3
   * 23 sources of rank 4

The Swift-XRT observations also covered the locations of 17 sources
reported by other observers, thus:

* DG19dnjlc (GCN25393)		F < 1.7x10^-12 erg cm^-2 s^-1.
* DG19gcwjc (GCN25393)		F < 2.2x10^-12 erg cm^-2 s^-1.
* DG19hqpgc (GCN25362)		F < 4.2x10^-13 erg cm^-2 s^-1.
* DG19kxdnc (GCN25393)		F < 1.1x10^-12 erg cm^-2 s^-1.
* DG19qabkc (GCN25362)		F < 2.9x10^-12 erg cm^-2 s^-1.
* DG19rtekc (GCN25393)		F < 1.6x10^-12 erg cm^-2 s^-1.
* DG19rzhoc (GCN25393)		F < 4.1x10^-12 erg cm^-2 s^-1.
* DG19sevhc (GCN25362)		F < 4.4x10^-12 erg cm^-2 s^-1.
* DG19tvtnc (GCN25393)		F < 4.0x10^-12 erg cm^-2 s^-1.
* DG19tzyhc (GCN25362)		F < 1.2x10^-12 erg cm^-2 s^-1.
* DG19wgmjc (GCN25362)		F < 4.3x10^-12 erg cm^-2 s^-1.
* DG19wlpmc (GCN25393)		F < 4.3x10^-12 erg cm^-2 s^-1.
* DG19wxnjc (GCN25393)		F < 3.8x10^-12 erg cm^-2 s^-1.
* desgw-190814a (GCN25336)	F < 5.2x10^-12 erg cm^-2 s^-1.
* desgw-190814d (GCN25373)	Matches source 26, rank 3, 7.0" away.
* desgw-190814e (GCN25373)	F < 2.8x10^-12 erg cm^-2 s^-1.
* desgw-190814f (GCN25398)	F < 1.0x10^-12 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 are online at

Swift is currently re-observing the GW error region with longer 
exposures to look for any late-rising emission.

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