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GCN Circular 34736

Subject
LIGO/Virgo S230917af: Swift XRT observations, 6 X-ray sources
Date
2023-09-19T15:22:26Z (a year ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
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),
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.G.
Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB),
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) and H. Negoro (Nihon U.),report on behalf of the
Swift team:

Swift has carried out 18 observations to tile the location of MAXI
J2215+39, a possible counterpart to the subthreshold GW trigger
S230917af (Negoro et al., GCN Circ. 34723Loading...
 
 ).

We have detected 6 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
  * 5 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   |
|  S230917af_X3  | 22h 13m 08.28s | +39d 32' 46.1" |	8.4" |


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   |
|  S230917af_X1  | 22h 17m 41.91s | +39d 19' 22.3" |	5.1" |
|  S230917af_X4  | 22h 14m 05.23s | +39d 38' 57.2" |	5.4" |
|  S230917af_X6  | 22h 16m 33.47s | +39d 51' 41.1" |	7.2" |
|  S230917af_X9  | 22h 13m 43.20s | +38d 55' 20.3" |	6.3" |
| S230917af_X10  | 22h 14m 50.64s | +38d 51' 07.1" |	6.7" |

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/S230917af

Further observations of S230917af_X3 have been requested.

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