GCN Circular 39009

K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU),
A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris
(U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini
(INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), J.J.
Delaunay (PSU), M. De Pasquale (University of Messina), S. Dichiara
(PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) , V. D’Elia
(ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson
University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin
(UCL-MSSL), S. Laha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P.
Osborne (U. Leicester), P. O’Brien (U. Leicester), M.J. Page
(UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato (INAF-OAB),
B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB),
E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team:

Swift has carried out 189 observations of the LVC error region for the
GW trigger S250119cv convolved with the 2MPZ catalogue (Bilicki et al.
2014, ApJS, 210, 9), using the 'BAYESTAR' (version BAYESTAR.fits.gz) 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 2.6 ks to 101 ks after the LVC trigger, and the XRT
has covered 13.1 deg^2 on the sky (corrected for overlaps). This covers
68% of the probability in the 'ligo-skymap-from-samples' (version
ligo-skymap-from-samples.fits.gz) skymap, and 69% after convolving with
the 2MPZ galaxy catalogue, as described by Evans et al. (2016, MNRAS, 
462, 1591).

We have detected 5 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
  * 1 source of rank 3
  * 4 sources 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   |
|  S250119cv_X6  | 03h 47m 22.56s | -74d 14' 45.7" |	8.9" |


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   |
|  S250119cv_X1  | 00h 56m 18.41s | +27d 53' 48.0" |	7.4" |
|  S250119cv_X4  | 00h 55m 50.96s | +26d 24' 41.2" |   12.8" |
|  S250119cv_X5  | 00h 58m 11.65s | +27d 34' 36.6" |	6.7" |
| S250119cv_X11  | 00h 58m 29.90s | +26d 39' 11.5" |	8.7" |

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, unless otherwise
stated.

The results of the XRT automated analysis, including details of the
sources listed above, are online at
https://www.swift.ac.uk/LVC/S250119cv

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