POEMMA's target-of-opportunity sensitivity to cosmic neutrino transient sources

We investigate the capability of the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) in performing target-of-opportunity (ToO) neutrino observations. POEMMA is a proposed space-based probe-class mission for ultrahigh-energy cosmic ray and very-high-energy neutrino detection using two spacecraft, each equipped with a large Schmidt telescope to detect optical and near-ultraviolet signals generated by extensive air showers (EASs). POEMMA will be sensitive to Cherenkov radiation from upward-moving EASs initiated by tau neutrinos interacting in the Earth. POEMMA will be able to quickly repoint (90 degrees in 500 s) each of the two spacecrafts to the direction of an astrophysical source, which in combination with its orbital speed will provide it with unparalleled capability to follow-up transient alerts. We calculate POEMMA's transient sensitivity for two observational configurations for the satellites (ToO-stereo and ToO-dual for smaller and larger satellite separations, respectively) and investigate the impact of variations arising due to POEMMA's orbital characteristics on its sensitivity to tau neutrinos in various regions of the sky. We explore separate scenarios for long (similar to 10(5)(-6) s) and short (similar to 10(3) s) duration events, accounting for intrusion from the Sun and the Moon in the long-duration scenario. We compare the sensitivity and sky coverage of POEMMA for ToO observations with those for existing experiments (e.g., IceCube, ANTARES, and the Pierre Auger Observatory) and other proposed future experiments (e.g., GRAND200k). For long bursts, we find that POEMMA will provide a factor of greater than or similar to 7 improvement in average neutrino sensitivity above 300 PeV with respect to existing experiments, reaching the level of model predictions for neutrino fluences at these energies and above from several types of long-duration astrophysical transients (e.g., binary neutron star mergers and tidal disruption events). For short bursts, POEMMA will improve the sensitivity over existing experiments by at least an order of magnitude for E-v greater than or similar to 100 PeV in the best-case scenario. POEMMA's orbital characteristics and rapid repointing capability will provide it access to the full celestial sky, including regions that will not be accessible to ground-based neutrino experiments. Finally, we discuss the prospects for POEMMA to detect neutrinos from candidate astrophysical neutrino sources in the nearby Universe. Our results demonstrate that with its improved neutrino sensitivity at ultrahigh energies and unique full-sky coverage, POEMMA will be an essential, complementary component in a rapidly expanding multimessenger network.