TITLE: GCN CIRCULAR NUMBER: 41196 SUBJECT: LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm DATE: 25/07/29 18:11:07 GMT FROM: Joe Durbak at UMD <gcn.joedurbak@gmail.com> LIGO/Virgo/KAGRA S250727dc : PRIME J-band upper limits of AT 2025smm J. Durbak (UMD), O. Guiffreda (UMD), N. Passaleva, M. El Kabir, A. S. Kutyrev (NASA/GSFC), E. Troja (U Rome), S. B. Cenko (NASA/GSFC) Following the LIGO/Virgo/KAGRA detection of S250727dc (GCN 41179), we observed a portion of the transient field in J-filter with PRIME ~32 hours after LVK detection. This field was chosen to overlap with the Swift UVOT detection of an uncatalogued source, AT 2025smm (GCN 41187). At the position of AT 2025smm reported by Swift UVOT (GCN 41187), we detect no sources in J-band. Using nearby 2MASS stars for preliminary calibration we derive the following limiting magnitude, not corrected for Galactic extinction: | Filter | Mag(AB) | |--------|--------------| | J | > 19.7 | 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/41196. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...