TITLE:   GCN CIRCULAR
NUMBER:  24541
SUBJECT: LIGO/Virgo S190510g: Swift-XRT observations and results
DATE:    19/05/14 14:56:23 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (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), 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 performed a series of 977 observations, covering 977 separate
locations within the LVC error region for the GW trigger S190510g
convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9),
using 226 fields from the 'bayestar' GW localisation map and 751 fields
from the 'LALInference' 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 7.2 ks to 270 ks after
the LVC trigger, and cover 76.9 sq degrees on the sky (corrected for
overlaps). This covers 58% of the probability in the 'LALInference'
skymap, and 67% 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 10% of the probability (14%
when convolved).

We have detected 33 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 http://www.swift.ac.uk/ranks.php.

We have found:

   * 0 sources of rank 1
   * 0 sources of rank 2
   * 5 sources of rank 3
   * 28 sources of rank 4

Details of these sources can be viewed online via 
http://www.swift.ac.uk/LVC/

For all GW triggers from O3 onwards, XRT results will appear on this 
page, once human verification has taken place to remove spurious sources.

Additionally, our search serendipitously covered the locations of some 
of the other reported candidates. In particular the location of 
DG19fqqk/desgw-190510c (GCNs 24467, 24480) was covered 4 times. No XRT 
source was found with a 3-sigma upper limit of 6.1 x 10^-2 ct/sec, 
corresponding to a 0.3-10 keV flux of 2.6 x 10^-12 erg cm^-2 s^-1. The 
location of DG19llhk (GCNs 24467) was covered 3 times with no detection 
found, down to a  3-sigma upper limit of 6.4 x 10^-2 ct/sec, 
corresponding to 2.8e-12 erg cm^-2 s^-1. Both flux conversions assume a 
power-law spectrum with photon index=1.7 and absorption column NH=3 x 
10^20 cm^-2.

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