GCN Circular 36698

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 198 observations of the LVC error region for the
GW trigger S240615dg 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 3.1 ks to 86 ks after the LVC trigger, and the XRT
has covered 10.1 deg^2 on the sky (corrected for overlaps). This covers
75% of the probability in the 'BAYESTAR' (version BAYESTAR.fits.gz)
skymap, and 75% after convolving with the 2MPZ galaxy catalogue, as
described by Evans et al. (2016, MNRAS,  462, 1591). These pointings
and associated metadata have been reported to the Treasure Map (Wyatt
et al., 2020, ApJ, 894, 127;
http://treasuremap.space/alerts?graceids=S240615dg).

We have detected 39 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
  * 38 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   |
|  S240615dg_X1  | 00h 29m 35.99s | +46d 06' 37.8" |	8.0" |
|  S240615dg_X2  | 00h 33m 50.16s | +45d 33' 03.6" |	8.1" |
|  S240615dg_X3  | 00h 24m 14.80s | +45d 53' 04.3" |	6.8" |
|  S240615dg_X4  | 00h 24m 34.85s | +46d 01' 51.6" |	8.4" |
|  S240615dg_X5  | 00h 23m 43.15s | +46d 00' 40.9" |	9.8" |
|  S240615dg_X6  | 16h 35m 45.42s | -72d 36' 59.3" |	7.3" |
|  S240615dg_X7  | 00h 35m 43.50s | +45d 29' 07.5" |	7.9" |
|  S240615dg_X8  | 00h 34m 53.17s | +45d 43' 42.7" |   10.9" |
| S240615dg_X10  | 16h 20m 44.43s | -72d 48' 53.5" |   17.2" |
| S240615dg_X11  | 16h 35m 48.47s | -71d 28' 36.4" |	8.5" |
| S240615dg_X12  | 00h 25m 17.22s | +45d 34' 26.4" |	6.1" |
| S240615dg_X13  | 00h 25m 32.31s | +45d 21' 11.6" |	6.2" |
| S240615dg_X14  | 00h 24m 18.85s | +45d 25' 10.0" |	5.1" |
| S240615dg_X15  | 00h 25m 03.91s | +45d 24' 20.8" |	5.3" |
| S240615dg_X16  | 00h 25m 51.20s | +45d 26' 38.4" |	6.6" |
| S240615dg_X17  | 00h 25m 27.73s | +45d 16' 04.9" |	5.5" |
| S240615dg_X18  | 00h 24m 41.47s | +45d 32' 05.4" |	6.9" |
| S240615dg_X19  | 00h 24m 22.40s | +45d 23' 33.9" |	6.4" |
| S240615dg_X20  | 00h 25m 37.33s | +45d 28' 04.1" |	6.0" |
| S240615dg_X21  | 00h 25m 05.70s | +45d 27' 57.8" |	6.4" |
| S240615dg_X22  | 00h 25m 32.43s | +45d 15' 12.0" |	5.9" |
| S240615dg_X23  | 00h 24m 30.74s | +45d 28' 38.2" |	6.6" |
| S240615dg_X24  | 00h 25m 10.83s | +45d 24' 54.6" |	6.9" |
| S240615dg_X25  | 00h 24m 23.90s | +45d 26' 50.1" |	6.4" |
| S240615dg_X26  | 00h 24m 59.37s | +45d 19' 18.3" |	6.6" |
| S240615dg_X27  | 00h 24m 58.39s | +45d 14' 29.3" |	8.0" |
| S240615dg_X28  | 00h 24m 59.44s | +45d 18' 29.4" |	6.2" |
| S240615dg_X29  | 00h 24m 25.17s | +45d 14' 37.8" |	7.1" |
| S240615dg_X30  | 00h 24m 16.62s | +45d 22' 58.5" |	7.1" |
| S240615dg_X31  | 00h 25m 02.99s | +45d 31' 50.9" |	6.2" |
| S240615dg_X32  | 00h 24m 55.02s | +45d 20' 08.0" |	7.4" |
| S240615dg_X33  | 00h 24m 32.36s | +45d 27' 19.6" |	7.7" |
| S240615dg_X34  | 00h 25m 27.36s | +45d 27' 36.6" |	7.8" |
| S240615dg_X35  | 00h 25m 39.51s | +45d 24' 31.2" |	6.4" |
| S240615dg_X36  | 00h 24m 14.08s | +45d 26' 02.9" |	7.1" |
| S240615dg_X37  | 00h 25m 26.55s | +45d 18' 05.9" |	9.7" |
| S240615dg_X38  | 00h 24m 25.04s | +45d 20' 56.7" |	6.8" |
| S240615dg_X39  | 00h 23m 53.86s | +45d 21' 51.6" |	7.2" |


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   |
|  S240615dg_X9  | 00h 27m 42.35s | +45d 14' 56.5" |	7.5" |

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/S240615dg

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