Collaborative Research: WoU-MMA: New Advancements to Enable Multi-Messenger Neutrino Astrophysics with the Radio Neutrino Observatory in Greenland

This award supports research in relativity and relativistic astrophysics and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. Observations of high energy astrophysical neutrinos further our understanding of the most powerful cosmic ray accelerators and explosive events in the universe. Combining astrophysical neutrino observations with observations from other messengers like photons, cosmic rays, and gravitational waves allows us to view the most violent processes in the universe through multiple lenses and make new insights into the physics that drives them. Neutrino observations with IceCube have shown that the neutrino sky is complex and dynamic, revealing both an unresolved, but steady, background of neutrinos and flares of neutrinos associated with a blazar. The work performed under this award will establish the first connection between a radio neutrino telescope and other multi-messenger observatories, expanding our multi-messenger view of the universe to include the highest-energy neutrinos. In addition, this work will enable a broad range of interdisciplinary science, from glaciology to biology, and engage people from a broad range of backgrounds from around the world in multi-messenger astrophysics. The Radio Neutrino Observatory in Greenland is currently under construction at Summit Station and is optimized to search for the radio flash generated by neutrino interactions in polar ice, building on the combined successes and expertise of earlier generations of radio detectors. Its leading sensitivity, large footprint, and precision pointing will deliver unprecedented measurements of the high-energy neutrino flux. RNO-G is also the first ultra-high energy neutrino observatory with a view of the Northern sky. As such it has unique capabilities for multi-messenger observations of the highest energy neutrinos sources, including those initiated by lower-energy neutrino observations made with IceCube. The work performed under this award will provide the necessary upgrades to the RNO-G project, as it is being built, to realize its potential as a state-of-the-art instrument fully integrated into the world-wide network of multi-messenger observatories. This proposed program will improve RNO-G's sensitivity and angular resolution and enable it to respond rapidly to important targets, necessary advancements for multi-messenger campaigns. This work will lay the groundwork to provide the broader multi-messenger community high-quality event reconstructions shortly after the first high-energy neutrino candidates are identified. Under this award, the proposal team will (1) enhance neutrino pointing resolution through improved antenna designs and coincident observations in multiple stations, (2) develop real-time event processing capabilities, allowing for quicker turnaround on candidates and increased trigger rates to improve sensitivity, and (3) enable RNO-G to respond to incoming multi-messenger alerts from leading observatories, temporarily boosting sensitivity in the alert direction. The team will use these advances to conduct the first searches for multi-messenger point sources and transient sources with RNO-G. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.