TITLE: GCN CIRCULAR NUMBER: 43185 SUBJECT: EP251220a: PRIME upper limit DATE: 25/12/22 16:55:31 GMT FROM: N. Passaleva at Sapienza University of Rome <niccolo.passaleva@uniroma1.it> N. Passaleva (U Rome), O. Guiffreda (UMD), M. El Kabir (U Rome), J. Durbak (UMD), E. Troja (U Rome), A. S. Kutyrev (NASA/GSFC), S. B. Cenko (NASA/GSFC) We observed the field of the optical counterpart (Sánchez Álvarez et al. GCN 43167) of the fast X-ray transient EP251220a (Liu et al., GCN 43162) in J filter with PRIME. Observations started ~35h after the trigger. Using Two Micron All Sky Survey (2MASS) nearby stars for preliminary calibration we do not detect any uncatalogued source down to J>20.5 AB (3-sigma) not corrected for galactic extinction at the position of the candidate reported by Sánchez Álvarez et al. (GCN 43167), Kumar et al. (GCN 43169), Busmann et al. (GCN 43181), van Hoof et al. (GCN 43182), An et al. (GCN 43184). 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/43185. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...