TITLE: GCN CIRCULAR NUMBER: 41205 SUBJECT: LIGO/Virgo/KAGRA S250727dc: Swift-UVOT follow up of AT 2025smm DATE: 25/07/30 20:28:25 GMT FROM: Paul Kuin at MSSL npkuin@gmail.com

N.P.M. Kuin (UCL-MSSL), M.H. Siegel (PSU), A.A. Breeveld (UCL-MSSL), C. Gronwall (PSU), N.J. Klingler (NASA/GSFC UMBC CRESST II),F.E. Marshall (NASA/GSFC), S.R. Oates (Lancaster U.), M. De Pasquale (University of Messina), M.J. Page (UCL-MSSL), S. Shilling (Lancaster U.), A. D’Aì (INAF-IAFPA), P. D’Avanzo (INAF-OAB), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB),S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), J.J. Delaunay (PSU), S. Dichiara (PSU), V. D’Elia (ASI-SSDC & INAF-OAR), R.A.J.Eyles-Ferris (U. Leicester), P.A. Evans (U. Leicester), R. Gayathri (PSU), D. Hartmann (Clemson University), J.A. Kennea (PSU), S. Laha (NASA/GSFC),H.A. Krimm (NSF), D. B. Malesani (DTU Space), P. O’Brien (U. Leicester), J.P. Osborne (U. Leicester), T. Parsotan (NASA/GSFC), M. Perri (ASDC), K.L. Page (U. Leicester), D.M. Palmer (LANL), S. Ronchini (PSU), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), G. Tagliaferri (INAF-OAB), E. Troja (U. Tor Vergata, INAF), and A. Tohuvavohu (U. Toronto)report:

Swift re-observed the location of AT 2025smm in the high-probability region of LIGO/Virgo/KAGRA S250725dc from 1.56 to 1.63 d after the trigger. The source is no longer detected. we obtained the following 3-sigma upper limits:

Filter Exposure(s) 3-sigma UL AB mag) UVW2 606 22.3 UVM2 466 21.8 UVW1 303 21.5 U 151 20.8 B 151 20.1 V 151 19.3

No corrections were made for interstellar extinction.

View this GCN Circular online at https://gcn.nasa.gov/circulars/41205. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...