TITLE: GCN CIRCULAR NUMBER: 41504 SUBJECT: LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz DATE: 25/08/22 23:39:31 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it> N. Passaleva (U Rome), J. Durbak (UMD), O. Guiffreda (UMD), E. Troja (U Rome), R.Hamada (Osaka U), A. S. Kutyrev (NASA/GSFC), D. Suzuki (Osaka U), T. Sumi (Osaka U), A. Idei (Osaka U), S. B. Cenko (NASA/GSFC) We observed the optical transient AT2025ulz/ZTF25abjmnps (Stein et al. GCN 41414; Hall et al. GCN 41433; Karambelkar et al. GCN 41436; O'Connor et al. GCN 41452) possibly associated to the GW candidate S250818k (LVKC GCN 41437) in H filter and in J filter with PRIME ~87.62 hours and ~111.62 hours after the GW trigger. Using nearby stars from the Two Micron All Sky Survey (2MASS; Skrutskie et al. 2006) for calibration we estimate a 3-sigma limiting magnitude of H>20 AB for the image. Within the transient's host galaxy we see no obvious point source, although template subtraction is required to place a meaningful upper limit to its brightness. PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023, Durbak et al. 2024). We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...