[vsnet-grb-info 23867] LIGO/Virgo S190930t: Swift XRT observations, no secure afterglow found

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  25966
SUBJECT: LIGO/Virgo S190930t: Swift XRT observations, no secure afterglow found
DATE:    19/10/07 07:20:45 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

P.A. Evans (U. Leicester), K.L. Page (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. Warwick), P.T. O'Brien (U.
Leicester), J.P. Osborne (U. Leicester), C. Pagani (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 649 observations of the LVC error region for the
GW trigger S190930t convolved with the 2MPZ catalogue (Bilicki et al.
2014, ApJS, 210, 9), using the 'bayestar' 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 7.6 ks to
345 ks after the LVC trigger, and the XRT has covered 71.6 deg^2 on the
sky (corrected for overlaps). This covers 0.5% of the probability in
the 'bayestar' skymap, and 2.5% after convolving with the 2MPZ galaxy
catalogue, as described by Evans et al. (2016, MNRAS,  462, 1591). Our
pointings have been uploaded to the "Treasure Map" web service:
http://treasuremap.space/alerts?graceids=S190930t.

We have detected 14 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.

One rank 3 source, "source 12", is of potential interest as it appears
to be fading. This source is at RA,Dec = 07h 47m 58.93s +43d 18' 20.1",

which is equivalent to:

RA(J2000.0)   = 116.99554
Dec(J2000)    = +43.3056

with an uncertainty of 8 arcsec (radius, 90% confidence). There is no
galaxy in 2MPZ near this location at a position consistent with the LVC

distance along this line of sight (105 Mpc), however, 2MPZ is only 75%
complete to this distance.


In total, we have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 5 sources of rank 3
  * 9 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/S190930t

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