GCN Circular 26475

P.A. Evans (U. Leicester), A. Keivani (Colombia U.), J.A. Kennea (PSU), A.
Tohuvavohu (U. Toronto), S. Countryman (Colombia U.), I. Bartos (U. Florida), D.
Fox (PSU), S. Marka (Colombia U.), Zsuzsa Marka (Colombia U.) 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 100 observations of the overlap between the LVC (GCN Circ.
26454
Not found
 
 
) and IceCube (GCN Circ. 26463
Not found
 
 
) error regions for the GW trigger S191216ap.
The observations span from 22 ks to 42 ks after the LVC trigger, and the XRT has
covered 10.2 deg^2 on the sky (corrected for overlaps). This covers 3.3% of the
probability in the bayestar skymap, and 5.8% after convolving with the 2MPZ
galaxy catalogue, as described by Evans et al. (2016, MNRAS, 462, 1591). It
covers 65% of the probability contained within the combined GW and neutrino
localisations. These pointings and associated metadata have been reported to the
Treasure Map (Wyatt et al., GCN Circ. 26244
Not found
 
 
;
http://treasuremap.space/alerts?graceids=S191216ap).

We have detected 3 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
  * 2 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/S191216ap

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