TITLE: GCN CIRCULAR NUMBER: 43220 SUBJECT: EP251221a: PRIME upper limit DATE: 25/12/23 17:54:25 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 fast x-ray transient EP251221a detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Dai et al. GCN 43178) in J and H filters with PRIME. Observations started ~24h 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>21 AB (3-sigma) not corrected for galactic extinction in the WXT error region. 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/43220. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...