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GCN Circular 26498

Subject
LIGO/Virgo S191216ap, Swift XRT observations: 16 X-ray sources in the HAWC error region search
Date
2019-12-19T09:22:13Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), 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 (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.J.
Klingler (PSU), 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. Birmingham), 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 further observations of S191216ap. We performed a
series of tiles to cover the HAWC error region (GCN Circ. 26472) for
500 s per tile, and then 3ks observations of each of the galaxies
listed by Singer et al (GCN Circ. 26479). All of the Swift pointings
and associated metadata have been reported to the Treasure Map (Wyatt
et al., GCN Circ. 26244;
http://treasuremap.space/alerts?graceids=S191216ap).

In these observations, we detected 17 X-ray sources, these are either
new detections, or have been given a higher 'rank' than in the last
circular. 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
  * 13 sources 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   |
|  S191216ap_X4  | 21h 33m 49.19s | +04d 57' 18.9" |	6.7" |
|  S191216ap_X5  | 21h 33m 18.81s | +05d 17' 04.9" |	6.9" |
|  S191216ap_X6  | 21h 34m 53.19s | +05d 19' 11.0" |	6.6" |
|  S191216ap_X7  | 21h 32m 44.20s | +04d 20' 06.0" |	5.8" |
|  S191216ap_X8  | 21h 32m 47.89s | +04d 27' 52.2" |	5.5" |
|  S191216ap_X9  | 21h 32m 26.75s | +04d 21' 31.6" |	5.3" |
| S191216ap_X10  |  21h 32m 6.50s | +04d 18' 38.2" |	6.9" |
| S191216ap_X12  | 21h 31m 46.59s | +05d 44' 44.4" |	7.0" |
| S191216ap_X13  | 21h 31m 56.80s | +05d 11' 22.4" |	8.0" |
| S191216ap_X17  | 21h 31m 43.77s | +05d 25' 15.7" |	6.0" |
| S191216ap_X19  | 21h 31m 57.63s | +04d 43' 38.4" |	7.4" |
| S191216ap_X20  | 21h 31m 31.98s | +04d 54' 03.0" |	5.0" |
| S191216ap_X21  | 21h 31m 44.49s | +05d 23' 12.0" |	7.4" |


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   |
| S191216ap_X11  | 21h 32m 41.01s | +04d 24' 18.6" |	6.2" |
| S191216ap_X14  | 21h 30m 32.91s | +05d 02' 18.4" |	7.6" |
| S191216ap_X15  | 21h 30m 26.31s | +05d 06' 07.0" |	7.2" |
| S191216ap_X16  | 21h 31m 22.64s | +05d 02' 37.5" |	5.4" |

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, including details of the
sources listed above, are online at
https://www.swift.ac.uk/LVC/S191216ap

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