[vsnet-grb-info 23052] LIGO/Virgo S190718y: Swift XRT observations, 45 X-ray sources

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25151
SUBJECT: LIGO/Virgo S190718y: Swift XRT observations, 45 X-ray sources
DATE:    19/07/25 13:36:34 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

P.A. Evans (U. Leicester), J.A. Kennea (PSU), N.J. Klingler (PSU), A.
Tohuvavohu (PSU), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U.
Leicester), M.G. Bernardini (INAF-OAB), 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), 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), 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 462 observations of the LVC error region for the
GW trigger S190718y convolved with the 2MPZ catalogue (Bilicki et al.
2014, ApJS, 210, 9), 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 13 ks to
365 ks after the LVC trigger, and the XRT has covered 30.9 sq degrees
on the sky (corrected for overlaps). This covers 17% of the probability
in the 'bayestar' skymap, and 22% after convolving with the 2MPZ galaxy
catalogue, as described by Evans et al. (2016, MNRAS,  462, 1591).

We have detected 45 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 https://www.swift.ac.uk/ranks.php.

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 27 sources of rank 3
  * 18 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=3x10^20 cm^-2, and photon index (Gamma)=1.7

The results of the XRT automated analysis are online at
https://www.swift.ac.uk/LVC/S190718y

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