TITLE: GCN CIRCULAR NUMBER: 34736 SUBJECT: LIGO/Virgo S230917af: Swift XRT observations, 6 X-ray sources DATE: 23/09/19 15:22:26 GMT FROM: Phil Evans at U of 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), 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. 34723). 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.