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GCN Circular 36314

Subject
LVK S240422ed: Further Swift-XRT followup of three sources
Date
2024-04-26T13:13:34Z (a month ago)
From
P.A. Evans at U. Leicester <pae9@leicester.ac.uk>
Via
email
P.A. Evans (U. Leicester), K.L. Page (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (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) report on behalf of the Swift team:

Swift has conducted follow-up observations of sources S240422ed_X61, S240422ed_X101 and S240422ed_X190, reported in GCN Circ. 36278. All three sources are now undetected with fading confirmed at at least the 3-sigma level.

On close inspection, we now believe that source S240422ed_X190 is not a real X-ray object. The XRT was operating at a higher-than-normal temperature when that object was detected and the image has an abnormally high background; further, the PSF of the source is not consistent with that expected for the reported count-rate, we thus believe this object can be dismissed.

Source S240422ed_X61 was detected initially with a count rate of (8.3 +/- 3.0) x 10^-2  ct s^-1;  in the latest observation it is undetected with a 3-sigma upper limit of 1.02 x 10^-2 ct s^-1.

Source S240422ed_X101 was detected initially with a count rate of 0.10 +/- 0.03 ct s^-1;  in the latest observation it is undetected with a 3-sigma upper limit of 1.05 x 10^-2 ct s^-1.

Both of these sources were also initially detected while the XRT temperature was elevated; however, there is no evidence of significantly increased background in those observations.
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