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Arxiv: TREASUREHUNT: Transients and Variability Discovered with HST in the JWST North Ecliptic Pole Time Domain Field Published: 1/10/2024 7:51:48 AM Updated: 4/12/2024 3:25:03 AM

Paper abstract: The JWST North Ecliptic Pole (NEP) Time Domain Field (TDF) is a >14 arcmindiameter field optimized for multi-wavelength time-domain science with JWST. Ithas been observed across the electromagnetic spectrum both from the ground andfrom space, including with the Hubble Space Telescope (HST). As part of HSTobservations over 3 cycles (the "TREASUREHUNT" program), deep images wereobtained with ACS/WFC in F435W and F606W that cover almost the entire JWST NEPTDF. Many of the individual pointings of these programs partially overlap,allowing an initial assessment of the potential of this field for time-domainscience with HST and JWST. The cumulative area of overlapping pointings is ~88arcmin^2, with time intervals between individual epochs that range between 1day and 4+ years. To a depth of m_{AB} ~eq 29.5 mag (F606W), wepresent the discovery of 12 transients and 190 variable candidates. For thevariable candidates, we demonstrate that Gaussian statistics are applicable,and estimate that ~80 are false positives. The majority of the transients willbe supernovae, although at least two are likely quasars. Most variablecandidates are AGN, where we find 0.42% of the general z < 6 field galaxypopulation to vary at the ~3\sigma level. Based on a 5-year timeframe, thistranslates into a random supernova areal density of up to ~0.07 transients perarcmin^2 (~245 deg^{-2}) per epoch, and a variable AGN areal density of~1.25 variables per arcmin^2 (~4500 deg^{-2}) to these depths.