16706

The Ultraviolet (UV) transient sky is one of the next frontiers in time-domain astrophysics with several space mission concepts planned for the middle of the decade. UV wavelengths are typically associated with hot phenomena comma but we are focused on their use in measuring shock breakout and shock cooling from core-collapse supernovae (CCSNe) at very early times. These extreme events correspond to the shock emerging from the surface of the progenitor. If properly sampled comma the UV peaks can be used to constrain properties of the progenitor stars comma including the energy per unit mass of the SN ejecta and the stellar radius. No previous HST UV time-domain survey had had the right depth and cadence to detect these events. Here we propose a 30 orbit (Small) Narrow-field Ultraviolet Transient Survey (NUTS) with WFC3 UVIS (F275W and F336W) comma which will represent the deepest and fastest UV time-domain survey to date. We intend for this survey to serve as a ''pathfinder.. to lay the foundation for future missions comma both with and without HST. The survey will reach a depth of >26 mag AB over 73 square arcmin with a cadence of 2 days over 6 epochs out to a redshift of 1.3. Coordinated observations with the deep comma ground-based Subaru Hyper Supreme Cam (HSC) SN survey will allow us to pinpoint the time and location of SNe. We expect the primary result of this survey to be the discovery of 2-3 shock cooling events comma approximately doubling the sample of existing events. The survey will also provide significant ancillary UV transient science comma including but not limited to SN shock interaction comma Type Ia non-degenerate companions comma and tidal disruption events.